male icr mice ( 25 - 32 g ), obtained from harlan ( dublin , va . ), were housed in groups of five . all animals were kept in a temperature - controlled ( 20 - 22 ° c .) environment with a 12 - hour light - dark cycle ( lights on at 7 a . m .). separate mice were used for testing each drug dose in the in vivo behavioral procedures . brain tissue for binding studies was obtained from male sprague - dawley rats ( 150 - 200 g ) purchased from harlan laboratories ( dublin , va .). measurement of spontaneous activity in mice occurred in standard activity chambers interfaced with a digiscan animal activity monitor ( omnitech electronics , inc ., columbus , ohio ). a standard tail - flick apparatus and a digital thermometer ( fisher scientific , pittsburgh , pa .) were used to measure antinociception and rectal temperature , respectively . resorcinols were synthesized in our labs ( organix , inc ., woburn , mass .) according to the procedure specified below and were suspended in a vehicle of absolute ethanol , emulphor - 620 ( rhone - poulenc , inc ., princeton , n . j . ), and saline in a ratio of 1 : 1 : 18 . drugs were administered to the mice intravenously ( i . v .) in the tail vein at a volume of 0 . 1 ml / 10 g . analogs o - 1376 and o - 1532 listed in table 1 were synthesized as previously described ( mahadevan et al ., 2000 ). analog o - 1601 was synthesized from 1 - deoxy - 9 - carbomethoxy cannabinol dmh analog ( mahadevan et al ., 2000 ) by lithium / liquid ammonia reduction as described for the preparation of o - 1376 . the compounds listed in tables 2 and 3 were prepared using a three step sequence ( fig1 ). the 2 - lithio derivative of 1 , 3 - dimethoxy - 5 -( 1 ′, 1 ′- dimethylheptyl ) resorcinol ( 1 ) was prepared using n - buli / hexane in thf . it was condensed with the appropriate ketone to give the tertiary alcohol 2 , which on treatment with trifluoroacetic acid / et3sih gave the dimethoxy precursors 3 . demethylation 2 with bbr 3 / ch 2 cl 2 gave the target compounds ( crocker et al ., 1999 ). the general procedure is illustrated in fig2 and described below . to a solution of the resorcinol 1 , ( 5 mmol ) in 25 ml of dry thf was added a 2 . 5 m solution of n - buli in hexane ( 5 . 5 mmol ) at 0 ° c . with stirring / n 2 . after additional stirring for 1 h at 0 ° c ., added a solution of the ketone ( 7 . 5 mmol ) in 3 ml of dry thf all at once . the solution was stirred for 0 . 5 h at 0 ° c . and then at 23 ° c . for 18 h . the reaction was worked up by the addition of sat nh 4 cl solution and extracted with ether . after washing ( h 2 o ) and drying ( na 2 so 4 ) the solvent was evaporated to give the crude tertiary alcohol 2 , which was used as such in the subsequent reaction . a solution of the tertiary alcohol 2 ( 5 mmol ) in 10 ml of dry ch 2 cl 2 was treated with cf 3 cooh ( 27 . 5 mmol ) followed by et 3 sih ( 12 . 5 mmol ). the solution was stirred / n 2 for 1 h or more ( followed by tlc ) and then quenched by the addition of sat nahco 3 solution . the organic layer was separated and after washing ( h 2 o ) and drying gave the crude dimethoxy precursor 3 of the target compound . this material was used as such for the demethylation step . treatment of 3 , as a solution in dry ch 2 cl 2 at 0 ° c ., with 3 equivalents of 1 n bbr 3 solution in ch 2 cl 2 , using the standard procedure and work up 2 , gave the crude target compound , which was purified by chromatography , generally using hexane / ethyl acetate mixtures . in the case of o - 1662 ( table 2 ), the corresponding tertiary alcohol 2 on treatment with cf 3 cooh / et 3 sih gave the unsaturated compound ( dehydrated but not reduced ) which on catalytic reduction ( pto 2 / c / h 2 ) in acetic acid gave the desired dimethoxy precursor 3 . the final compound was purified by chromatography using 5 % et 3 nh 2 / etoac mixture . the unsaturated analog o - 1423 ( table 2 ) was prepared by treatment of the corresponding tertiary alcohol 2 with cf 3 cooh alone in ch 2 cl 2 followed by demethylation . in table 3 , compounds o - 1797 - a and o - 1798 - b were diastereomeric mixtures and showed as two distinct spots in tlc which were separated by column chromatography , whereas o - 1657 was a sample of the mixture of diastereomers o - 1797 - a and o - 1798 - b . the dimethoxy compounds listed in tables 4 and 5 were prepared ( fig2 ) from 1 and the appropriate ketones using buli , as in the preparation of 2 , and isolating and purifying the compounds by chromatography ( ethyl acetate / hexane mixtures ). deprotection of o - 2092 was carried out by treatment with 10 % hcl in a ether / thf ( 5 : 4 ) mixture for 0 . 5 h at 23 ° c . to give a mixture of o - 2115 ( major ) and the dehydrated compound o - 2114 ( minor ). sodium borohydride reduction of o - 2115 furnished a mixture of diastereomeric compounds which were separated by chromatography to give the target compounds o - 2116 - a and o - 2117 - b . similarly o - 1966 - a and o - 1967 - b were separated from a diastereomeric mixture by chromatography . epoxidation of o - 2114 followed by nabh 4 reduction gave the target compound o - 2122 . in the preparation of o - 2090 the corresponding diethoxy resorcinol derivative of 1 was used in place of 1 . all compounds showed appropriate 1 hnmrs ( jeol eclipse 300 mhz ) and were characterized on the basis of their 1 hnmrs , tlc , and elemental analyses . prior to testing in the behavioral procedures , mice were acclimated to the experimental setting ( ambient temperature 22 - 24 ° c .) overnight . pre - injection control values were determined for rectal temperature and tail - flick latency ( in sec ). five min after i . v . injection with drug or vehicle , mice were placed in individual activity chambers and spontaneous activity was measured for 10 min . activity was measured as total number of interruptions of 16 photocell beams per chamber during the 10 - min test and expressed as % inhibition of activity of the vehicle group . tail - flick latency was measured at 20 min post - injection . maximum latency of 10 sec was used . antinociception was calculated as percent of maximum possible effect {% mpe =[( test − control latency )/( 10 - control )]× 100 }. control latencies typically ranged from 1 . 5 to 4 . 0 sec . at 30 min post - injection , rectal temperature was measured . this value was expressed as the difference between control temperature ( before injection ) and temperatures following drug administration (° c .). different mice ( n = 5 - 6 per dose ) were tested for each dose of each compound . each mouse was tested in each of the 3 procedures . the methods used for tissue preparation and binding have been described previously ( compton et al ., 1993 ) and are similar to those described by devane et al . ( 1988 ). all assays , as described briefly below , were performed in triplicate , and the results represent the combined data from three to six individual experiments . following decapitation and rapid removal of the brain , whole brain was homogenized and centrifuged . the resulting pellet was termed p 1 . the supernatant was saved and combined with the two subsequent supernatants obtained from washing of the p 1 pellet . the combined supernatant fractions were centrifuged , resulting in the p 2 pellet . after further incubation and centrifuging , this pellet was resuspended in assay buffer to a protein concentration of approximately 2 mg / ml . the membrane preparation was quickly frozen in a bath solution of dry ice and 2 - methylbutane ( sigma chemical co ., st . louis , mo . ), then stored at − 80 ° c . for no more than 2 weeks . prior to performing a binding assay an aliquot of frozen membrane was rapidly thawed and protein values determined by the method of bradford ( 1976 ). binding was initiated by the addition of 150 • g of p 2 membrane to test tubes containing 1 nm of [ 3 h ] cp 55 , 940 ( 79 ci / mmol ) and a sufficient quantity of buffer to bring the total incubation volume to 1 ml . nonspecific binding was determined by the addition of 1 • m unlabeled cp 55 , 940 . following incubation at 30 ° c . for 1 hr , binding was terminated by addition of ice cold buffer and vacuum filtration through pretreated filters in a 12 - well sampling manifold ( millipore , bedford , mass .). after washing , filters were placed into plastic scintillation vials ( packard , downer grove , ill .) and shaken . the quantity of radioactivity present was determined by liquid scintillation spectrometry . membranes for cb 2 binding were obtained from cho cells . the transfected cell line was maintained in dublecco &# 39 ; s modified eagle medium ( gibco brl , grand island , n . y .) with 10 % fetal clone ii ( hyclone laboratories , inc ., logan , utah ) plus 0 . 3 to 0 . 5 mg / ml g418 ( to maintain selective pressure ) under 5 % co 2 at 37 % c . cells were harvested with 1 mm edta in phosphate - buffered saline and were centrifuged at 1000 × g for 5 min at 4 % c . the supernatant was saved and the p1 pellet was resuspended in centrifugation buffer . homogenization and centrifugation were repeated twice and the combined supernatant fractions were centrifuged at 40 , 000 × g for 30 min at 4 % c . the p2 pellet was resuspended in centrifugation buffer 2 ( tris hcl , 50 mm ; edta , 1 mm ; and mgcl 2 , 3 mm , ph 7 . 4 ) to a protein concentration of approximately 2 mg / ml . protein concentrations were determined by the method of bradford ( 1976 ) using bio - rad protein assay ( bio - rad , richmond , calif .) and bsa standards ( fatty acid free , sigma chemical co ., st . louis , mo .). the membrane preparation was divided into amounts convenient for binding assays and frozen rapidly in dry ice and stored at − 80 % c . binding was initiated by the addition of 50 • g of quickly thawed p2 membranes to test tubes containing [ 3 h ] cp - 55 , 940 ( final reaction concentration 0 . 5 nm ), an appropriate concentration of unlabeled cp - 55 , 940 or test drug , and sufficient quantity of assay buffer ( 50 mm tris - hcl , 1 mm edta , 3 mm mgcl 2 , 5 mg / ml bovine serum albumin , ph 7 . 4 ) to bring the total incubation volume to 0 . 5 ml . concentration of [ 3 h ] cp - 55 , 940 in saturation studies ranged from 50 to 10 , 000 pm . nonspecific binding was determined by the addition of 1 • m unlabeled cp - 55 , 940 . cp - 55 , 940 and all cannabinoid analogs were - prepared by suspension in assay buffer from a 1 mg / ml ethanolic stock without evaporation of the ethanol ( final concentration of no more than 0 . 4 %). in competition studies , analog concentrations ranged from 0 . 1 nm to 10 • m . after incubation at 30 % c for 1 hr , binding was terminated by the addition of 2 ml of ice - cold wash buffer ( 50 mm tris - hcl and 1 mg / ml bsa ) and vacuum filtration through pre - treated filters in a 12 - well sampling manifold ( millipore , bedford , mass .). reaction vessels were washed once with 2 ml of ice - cold wash buffer . filters were placed into 7 - ml plastic scintillation vials ( rpi corp ., mount prospect , ill .) with 4 ml of budget - solve ( rpi corp .). after shaking for 30 min , the radioactivity present was determined by liquid scintillation spectrometry . three reaction vessels were used for each drug concentration in each assay . the results represent the combined data of three independent experiments . all assays were performed in siliconized test tubes , which were prepared by air drying ( 12 hr ) inverted borosilicate tubes after two rinses with a 0 . 1 % solution of aquasil ( pierce , rockford , ill .). the gf / c glass - fiber filters ( 2 . 4 cm , baxter , mcgaw park , ill .) were pre - treated in a 0 . 1 % solution of ph 7 . 4 polyethylenimine ( sigma chemical co .) for at least 6 hr . based on data obtained from numerous previous studies with cannabinoids , maximal cannabinoid effects in each procedure were estimated as follows : 90 % inhibition of spontaneous activity , 100 % mpe in the tail flick procedure , and − 6 ° c . change in rectal temperature . ed 50 &# 39 ; s were defined as the dose at which half maximal effect occurred . for drugs that produced one or more cannabinoid effect , ed 50 &# 39 ; s were calculated separately using least - squares linear regression on the linear part of the dose - effect curve for each measure in the mouse tetrad , plotted against log 10 transformation of the dose . for the purposes of potency comparison , potencies were expressed as μmol / kg . pearson product - moment correlation coefficients ( with associated significance tests ) were calculated between cb 1 binding affinity ( expressed as log k i ) and in vivo potency for each measure ( expressed as log ed 50 in μmol / kg ) for all active cannabinoid compounds that bound to the cb 1 receptor . in addition , multiple linear regression was used to calculate the overall degree of relationship between cb 1 binding affinity and potency in the mouse measures for all active cannabinoids . a correlation between cb 1 and cb 2 binding affinities was calculated for all compounds that had measurable k i &# 39 ; s for cb 1 and cb 2 binding ( k i & lt ; 10 , 000 nm ). ki values for cb 1 and cb 2 binding were obtained from scatchard displacement analysis as determined via ebda program of the kell software package ( biosoft , milltown , n . j .). the cb 1 and cb 2 binding affinities for substituted biphenyl analogs are shown in table 1 . these compounds contain a phenolic hydroxyl and a lipophilic side chain in the same orientation as in cannabinol . in addition , the pyran oxygen is absent and the analogs have substituents in the phenyl ring ( ring c ) of cannabinol . two of the analogs ( o - 1376 and o - 1601 ) have a dimethylheptyl side chain ; each possessed good cb 1 and cb 2 binding affinities and in vivo activity . o - 1601 , the more potent of the two active compounds , had a hydroxymethyl group in the phenyl ring . this substitution increased cb 1 affinity and in vivo potencies compared to o - 1376 , but did not affect affinity for cb 2 receptors . a similar effect is observed in the cannabinol series where the substitution of a hydroxymethyl group for a methyl at c - 9 in cannabinol increased binding affinity and potency ( mahadevan et al ., 2000 ). shortening the side chain of o - 1376 to dimethylbutyl ( o - 1532 ) severely decreased affinity for both receptors and resulted in loss of in vivo activity . table 2 presents binding and in vivo data for a series of 2 - cyclic ring substituted - 5 - dimethylheptyl resorcinols . manipulation of the size of the cyclic structure attached at position 2 of the resorcinol ring resulted in changes in binding affinities and potencies . substitution of a cyclopentane ring ( o - 1424 ) resulted in moderate affinity for the cb 1 receptor with excellent affinity for the cb 2 receptor . although this compound was active in all three in vivo assays , potency was relatively poor . in addition , potencies across the measures were not equal ; i . e ., potency for reducing spontaneous activity was approximately half that for producing antinociceptive and hypothermic effects . increasing ring size to a cyclohexane ( o - 1422 ), cycloheptane ( o - 1656 ), or adamantyl ( o - 1660 ) improved affinity 5 - to 14 - fold for both cannabinoid receptors and greatly increased potencies in vivo . substitution of a sulfur for a carbon in a cyclohexane ring ( o - 1425 ) decreased cb 1 affinity by 14 - fold and cb 2 affinity by 8 - fold ( compared to o - 1422 ) as well as reducing in vivo potencies . similarly , sulfur substitution in a cyclopentane ring ( o - 1661 ) also attenuated binding to both cannabinoid receptors . when a methylated nitrogen ( o - 1662 ) was inserted into the cyclohexane ring in the same position as the sulfur of o - 1425 , binding to cb 1 receptors did not occur . in addition , cb 2 binding was drastically decreased and the compound was not fully active in vivo . in contrast , placing a double bond in the cyclohexane ring ( o - 1423 ) decreased affinities and potencies , but the compound remained active . however , moving the lipophilic side chain of o - 1422 from c - 5 to c - 4 and replacing the dmh with a n - hexyl chain ( o - 2010 ) produced a 865 - fold decrease in cb 1 affinity and a loss of activity in vivo . table 3 shows results of tests with cyclohexane substituted resorcinols in which the position of the substituent at the cyclohexane ring attached to the core resorcinol was varied . all compounds were diastereomeric mixtures . all of these analogs had good ( k i = 2 nm ) to moderate ( k i = 144 nm ) affinity for cb 1 receptors and were cb 2 - selective ( k i range = 0 . 3 - 13 nm ). methylation at the 2 position of the cyclohexane ring ( o - 1658 ) did not dramatically alter affinity for either cannabinoid receptor or in vivo potencies compared to the corresponding cannabinoid with a non - methylated cyclohexane ( o - 1422 in table 2 ). moving the methyl to position 4 of the cyclohexane ring ( o - 1659 ) decreased affinity for both cannabinoid receptors by about 5 - fold and produced an even greater decrease ( 11 - to 24 - fold ) in potencies in vivo . substituting a phenyl group for the methyl at this same position ( o - 1663 ) resulted in 2 - to 3 - fold decreases in cb 2 and cb 1 affinities , respectively , and a loss of activity in vivo . in the next five analogs shown in table 3 , the methyl was attached at position 3 of the cyclohexane ring . o - 1657 exhibited cb 1 and cb 2 affinities that were similar to those of o - 1658 ; however , the profiles of in vivo potencies differed . whereas the two analogs showed approximately equal potencies in suppressing spontaneous activity , o - 1658 was twice as potent in producing antinociception and three times as potent in reducing body temperature . by careful chromatography , compound o - 1657 was separated into two distinct entities which were designated o - 1797 - a and o - 1798 - b . these analogs were still mixtures . affinities of o - 1797 - a and o - 1798 - b were 2 - 3 times greater than those of o - 1657 . while potencies of these isomers for suppression of locomotor activity and hypothermia were not notably different from those of o - 1657 , antinociceptive potencies were reduced by about half . the 3r isomer of this series ( o - 1826 ) showed decreased affinity for cb 1 receptors compared to o - 1657 ; however , affinity for cb 2 receptors was identical for both compounds . not surprisingly , given its decreased cb 1 affinity , o - 1826 was less potent than o - 1657 in vivo . substitution of a dimethylbutyl for the dmh side chain at c5 of the resorcinol component ( o - 1890 ) decreased affinities for both cannabinoid receptors . this compound was active in vivo , although potency was notably low for all measures . in contrast , addition of a gem - dimethyl group at the 3 position of the cyclohexane ring with retention of the dmh side chain of the resorcinol component ( o - 1871 ) resulted in the best cb 1 and cb 2 affinities of this series . in vivo potencies , however , were lower than expected for this compound , given its higher cb 1 binding affinity . in order to develop cb 2 selective ligands , we examined cyclic ring substituted dimethoxy resorcinols . the cb 1 and cb 2 binding affinities of these analogs are shown in tables 4 and 5 . although most of the compounds shown in tables 4 and 5 possessed a dimethylheptyl side chain , all had poor cb 1 affinity ; hence , they were not tested in vivo . the bicyclic structure of o - 1999 ( table 4 ) was almost identical to that of o - 1657 ( table 3 ), an analog with good cb 1 and cb 2 affinities and potent in vivo effects . both compounds had a dimethylheptyl side chain attached to the 5 position of a resorcinol core that was attached at position 2 to a cyclohexane ring . each compound had a methyl group at the 3 position of the cyclohexane ring . the major structural difference between the two compounds was that o - 1999 was a dimethoxy derivative of the resorcinol o - 1657 . this seemingly minor structural change from a phenol to a methoxy derivative resulted in complete loss of affinity for cb 1 receptors and an almost 600 - fold reduction in affinity for cb 2 receptors . similarly , the other analogs that were dimethoxy derivatives of the corresponding resorcinols had poor affinity for cb 1 receptors ( k i ranged from 1716 to & gt ; 10 , 000 ), regardless of the cyclic ring substitution at position 2 . in contrast , cb 2 binding affinities for some of these analogs remained high , as described in more detail below . table 4 presents binding data for 2 - cyclic ring substituted dimethoxy - resorcinol - dmh analogs that contain at least one oxygen inserted into or attached to the non - resorcinol cyclohexane ring . compared to o - 1999 which did not contain an oxygen in the cyclohexane ring , conversion of the cyclohexane ring to a pyran ring ( o - 1964 ) decreased cb 2 affinity almost 2 - fold without effect on cb 1 binding . further addition of a double bond at position 3 of the pyran ring resulted in o - 1965 which did not bind to either cannabinoid receptor . in contrast , the introduction of a tertiary hydroxyl group at c - 4 of the pyran ring ( o - 1962 ) increased cb 2 affinity by 3 - fold . adding additional oxygens such as a ketol group attached at c - 4 to the point of attachment of the dimethoxy resorcinol substituent ( o - 2092 ) also increased cb 2 affinity whereas adding an oxygen as an epoxide ( o - 2122 ) decreased it . the presence of a ketone group at c - 4 of the cyclohexane ring and having unsaturation in the ring ( o - 2114 ) resulted in a compound with poor affinity for either cannabinoid receptor ; however , if a tertiary hydroxyl group was added at the site of dimethoxy resorcinol attachment ( o - 2115 ), cb 2 affinity improved . retention of the tertiary hydroxyl , methylation at position 5 and the presence of a ketone at position 3 of the cyclohexane ring increased affinity for both receptors and resulted in a compound ( o - 2123 ) with the best affinity ( k i = 125 nm ) in this series . table 5 shows cb 1 and cb 2 affinities for 2 - cyclic ring substituted dimethoxy - resorcinol - dmh analogs in which the ring size and the position of the methyl or hydroxyl substituent on the cyclohexane ring are varied . the first analog ( o - 2072 ) contains one hydroxyl attached to the cyclohexane at the same position at which the resorcinol core is attached . this compound is cb 2 - selective . while it had poor affinity for cb 1 receptors , it bound with moderate affinity to cb 2 receptors . introduction of a methyl substituent in the 3 position of the cyclohexane ring gave a diastereomeric mixture from which two distinct entities were separated by careful chromotography . these analogs ( o - 1966 - a and o - 1967 - b ) were still mixtures . this substitution resulted in a 5 - fold increase in affinity for cb 2 receptors with continued poor affinity for cb 1 receptors . however , one of these isomers ( o - 1966 - a ) showed the best cb 2 selectivity ( 225 - fold ) in the series and had high binding affinity for the cb 2 receptor ( k 1 = 22 . 5 nm ). addition of an extra hydroxyl group to the cyclohexane ring ( o - 2121 ) reduced both selectivity and binding affinity for the cb 2 receptor comparable to those obtained with o - 1967 - b . removal of the methyl at position 3 and addition of an hydroxyl at position 4 resulted in two diastereomeric mixtures which could be separated that were designated as o - 2116 - a and o - 2117 - b . both of these isomers had poor affinity for cb 1 receptors , but while the b isomer also had poor affinity for cb 2 receptors , the a isomer bound to cb 2 receptors with moderate affinity . attachment of a gem - dimethyl group to position 3 of o - 2072 ( i . e ., o - 2068 ) did not significantly alter affinities for cb 1 or cb 2 receptors ; however , replacement of the dmh group of o - 2068 with a methyl group ( o - 2139 ) produced loss of affinity at both receptors . changing the dimethyoxy groups of the resorcinol by adding diethoxy groups ( o - 2090 ) drastically decreased affinities for cb 1 and cb 2 receptors ( compare o - 2090 to o - 1966 - a or o - 1967 - b ). enlarging the cyclohexane ring in o - 2072 to a cycloheptane ring ( o - 2091 ) resulted in little change in affinity for cb 1 receptors and an almost 2 - fold increase in cb 2 affinity . as stated in the introduction , the lack of cb 1 binding affinity of cannabidiol compared to other pyran - ring open analogs such as cp 55 , 940 prompted us to examine the structure - activity relationships of resorcinol derivatives for in vitro and in vivo cannabinoid activity . our results show that many of the structural changes that affect cb 1 receptor recognition and activation in traditional bicyclic and tricyclic cannabinoids similarly alter binding and activity in this resorcinol series . previous research has shown that the length and branching of a lipophilic substituent is important for cb 1 receptor recognition in all of the major cannabinoid agonist classes , including tetrahydrocannabinols ( compton et al ., 1993 ), bicyclic cannabinoids ( compton et al ., 1993 ), indole - derived cannabinoids ( wiley et al ., 1998 ), and anandamides ( ryan et al ., 1997 ; seltzman et al ., 1997 ). in the tricyclic and bicyclic series , a 1 ′, 1 ′- dimethylheptyl side chain is optimal ( compton et al ., 1993 ) and is contained in most of the resorcinols presented here . reducing the length of this substituent to 1 ′, 1 ′- dimethylbutyl ( o - 1532 and o - 1890 ) or methyl ( o - 2139 ) or a hydrogen ( o - 2010 ) resulted in a concomitant elimination or decrease in cb 1 receptor recognition , as occurs in other cannabinoid series with similar structural manipulations ( see references above ). other structural features affecting cb 1 receptor recognition and activation in this resorcinol series are related to the size , saturation , substitution , and methylation of the second , non - resorcinol ring of these bicyclic cannabinoids . in most tricyclic and bicyclic cannabinoids , the ring corresponding to the non - resorcinol ring in the current series is a cyclohexane . reducing this size to a cyclopentane decreases cb 1 affinity and potency whereas increasing it to a cycloheptane has little effect . substitution of an adamantyl results in better cb 1 affinity ; however , potency is decreased . similar modifications of tricyclic and bicyclic cannabinoids have not been reported . the degree of saturation of the cyclohexane ring , however , has been manipulated in several cannabinoid classes . in the resorcinol series , the presence of a cyclohexane ring appeared optimal , although a thorough investigation of this issue was not undertaken . introduction of a single double bond ( o - 1423 ) within the ring decreased cb 1 affinity and potency to the same extent as did a reduction in the size of the ring to a cyclopentane . hence , most structural manipulations were performed upon a bicyclic resorcinol - cyclohexane template . degree of saturation of , as well as the position of the double bond in the cyclohexane ring of tricyclic and bicyclic cannabinoids and in the polyolefin loop of the anandamides , has also been shown to affect cb 1 receptor recognition and activity in these cannabinoid classes . greatest affinity and potency within the anandamides is achieved with four double bonds , with greater or lesser saturation resulting in a reduction in cb 1 binding and / or in vivo activity ( adams et al ., 1995 ; sheskin et al ., 1997 ; thomas et al ., 1996 ). similarly , number and position of double bonds within the cyclohexane ring of tetrahydrocannabinols and bicyclic cannabinoids affect activity . for example , moving the double bond of δ 9 - thc to position δ 8 ( as in δ 8 - thc ) decreases cb 1 affinity three - fold and somewhat reduces potency ( compton et al ., 1993 ). unsaturation of the cyclohexane ring results in cannabinol with its greatly reduced cb 1 affinity ( showalter et al ., 1996 ). in contrast , cp 55 , 940 , with a completely saturated cyclohexane ring , is several fold more potent than δ 8 - thc - dmh which has a single double bond in the cyclohexane ring , but δ 8 - thc with its single double bond binds with better cb 1 affinity than does δ 9 ( 11 ) - thc which has a completely saturated cyclohexane ring ( compton et al ., 1993 ). the most remarkable structural features of the resorcinol series affecting cb 1 affinity , however , are the length of the lipophilic side chain at position 5 and the size of the cyclic ring substituent at position 2 of the resorcinol core . thc and cp 55 , 940 contain two oxygens : one as a phenol ( one hydroxyl in the aromatic ring ) with a second oxygen incorporated into a separate ring ( pyran oxygen in thc ) or a hydroxyl group attached as a substituent in the cyclohexane ring as in cp 55 , 940 . previous research has shown that eliminating the phenolic hydroxyl of δ 8 - thc - like cannabinoids results in deoxy - thc analogs that are cb 2 - selective ( huffman et al ., 1999 ). although some of these deoxy - thc analogs also retain reasonable affinity for cb 1 receptors , orientation of their binding to cb 1 receptors may be inverted such that the pyran oxygen substitutes for the absent phenolic hydroxyl in hydrogen bonding ( huffman et al ., 1996 ). in the absence of a pyran oxygen , as in the resorcinols , the nature of the substituent at position 2 of the resorcinol core is important to maintain adequate cb 1 affinity for in vivo activity . an acyclic ring was found to be better than a heterocyclic ring with a cyclohexane ring being optimal for in vivo activity . in addition , the size and the position of the substituent on the cyclic ring is important to maintenance of cb 1 affinity . the presence of a methyl substituent at position 3 enhanced activity in some cases . further , the 3r analog ( o - 1826 ; table 2 ) has a poorer . cb 1 binding affinity ( k i = 40 nm ) compared to the diastereomeric mixture o - 1657 ( k i = 14 nm ; table 2 ), suggesting that cb 1 binding affinity is enhanced when the orientation of the methyl substituent at position 3 in the cyclohexane ring is 3s compared to 3r . methylation of the phenols of the resorcinols drastically decreased or eliminated cb 1 affinity , perhaps because hydrogen donation is less likely from a methoxy group than from thc &# 39 ; s free hydroxyl group ( b . r . martin , unpublished observations ). similarly , methoxy substitution for the phenolic hydroxyl in the methyl esters of δ 8 - and δ 9 ( 11 ) - thc - dmh resulted in analogs that were cb 2 - selective and had little affinity for cb 1 receptors ( gareau et al ., 1996 ; huffman et al ., 1999 ; ross et al ., 1999 ). notably , with the exception of a few compounds , the dimethoxyresorcinols tested here were cb 2 - selective . most of the structural features that affected recognition at cb 1 receptors also affected cb 2 receptor recognition , although not always to the same degree or in the same manner . these factors included length and branching of the side chain and size and degree of saturation of the non - resorcinol cyclohexane ring . in a sar study on a series of cb 2 - selective deoxy - δ 8 - thc analogs , huffman et al . ( 1999 ) reported that length and branching of the c3 side chain affected cb 2 binding in a manner similar to its effect on cb 1 affinity , as it did in the present study ; however , the range of chain lengths for which moderate to good cb 2 affinity was retained for the deoxy - δ 8 - thc analogs was greater than the range for cb 1 affinity . similar results were obtained with a series of cb 2 - selective indole - derived cannabinoids in which length of the nitrogen substituent was varied ( aung et al ., 2000 ). to date , anandamide analogs appear to be cb 1 - selective with relatively little affinity for cb 2 receptors across several types of manipulations ( showalter et al ., 1996 ). insufficient research is available to determine the effect of substitution on a cyclohexane ring on cb 2 affinity across cannabinoid classes . other structural manipulations eliminated or drastically reduced cb 1 receptor recognition , but did not necessarily alter cb 2 receptor binding in an identical manner . as mentioned , cb 2 selectivity was most evident in the dimethoxy analogs , primarily as a consequence of severe reductions in cb 1 affinity . hu - 308 , the most selective cb 2 agonist to date , has a dimethoxy resorcinol core structure and does not bind to cb 1 receptors at all ( hanu_et al ., 1999 ). in addition , greater tolerance in cb 2 ( vs . cb 1 ) receptor recognition was observed with other c2 substitutions in the resorcinols . huffman et al . ( 2001 ) recently reported that bicyclic pyridone analogs with carbonyl substitution at c1 and a nitrogen substituent substitution at c2 of thc had little affinity for cb 1 receptors . in contrast , moderate cb 2 affinity ( ki = 53 nm ) was retained . differences in allosteric regulation of cb 1 and cb 2 receptors by ions and guanine nucleotides has been noted previously ( showalter et al ., 1996 ). together , results presented here and elsewhere ( see above ) suggest incomplete overlap of the pharmacophores for cb 1 and cb 2 receptors . in summary , structure - activity relationships of the resorcinol series presented here are consistent with the cb 1 and cb 2 pharmacophores of other cannabinoid classes , including tetrahydrocannabinols , bicyclic cannabinoids , aminoalkylindoles , and anandamides . in this series of resorcinols , several structural features were essential for maintenance of cb 1 receptor recognition and in vivo activity , including the presence of a branched lipophilic side chain ( dmh ) at c5 , the presence of free phenols , and substitution of a cyclohexane ring at c2 . an important structural feature for receptor recognition at cb 2 receptors was side chain length , as reduction of the chain length to a methyl eliminated cb 2 binding affinity . the cb 2 selectivity observed with some resorcinols was maximized in the dimethoxyresorcinol analogs and this selectivity was greatly enhanced when a tertiary hydroxyl group was present in the cyclohexane ring in the same position at which the resorcinol core is attached . in contrast , the presence of unsaturation or a ketone group or an additional hydroxyl substitution in the cyclohexane ring adversely affected the cb 2 selectivity . methyl ethers were optimal for cb 2 selectivity since ethyl ethers reduced selectivity . in conclusion , although resorcinol derivatives with cyclic ring substituents at c2 are closely related to the nonactive cannabinoid cannabidiol , many of these analogs have high cb 1 and / or cb 2 binding affinity as well as potent in vivo activity . in addition , because dimethoxyresorcinols are cb 2 selective , they have potential to offer insight into similarities and differences between requirements for receptor recognition at cb 1 versus cb 2 receptors . one such difference noted here was the greater tolerance found for substitution at position 2 , in the resorcinol series , for cb 2 receptor recognition compared to that for cb 1 receptors . the results presented here suggest that the resorcinol series represent a novel template for the development of cb 1 and cb 2 selective cannabinoid agonists . while the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment , it is to be understood that the invention is not to be limited to the disclosed embodiment , but on the contrary , is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims . adams i b , ryan w , singer m , thomas b f , compton d r , razdan r k , martin b r ( 1995 ) evaluation of cannabinoid receptor binding and in vivo activities for anandamide analogs . j pharmacol exp ther 273 : 1172 - 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135 . devane w a , dysarz iii f a , johnson m r , melvin l s , and howlett a c ( 1988 ) determination and characterization of a cannabinoid receptor in rat brain . mol pharmacol 34 : 605 - 613 . gareau y , dufresne c , gallant m , rochette c , sawyer n , slipetz d m , tremblay n , weech p k , metters k m , labelle m ( 1996 ) structure activity relationships of tetrahydrocannabinol analogues on human cannabinoid receptors . bioorg med chem 6 : 189 - 194 . hanu_l , breuer a , tchilibon s , shiloah s , goldenberg d , horowitz m , pertwee r g , ross r a , mechoulam r ( 1999 ) hu - 308 : a specific agonist for cb2 , a peripheral cannabinoid receptor . proc nat acad sci usa 96 : 14228 - 14233 . huffman j w , lu j , hynd g , wiley j l , martin b r ( 2001 ) a pyridone analogue of traditional cannabinoids . a new class of selective ligands for the cb 2 receptor . bioorg med chem , in press . huffman j w , liddle j , yu s , aung m m , abood m e , wiley j l , martin b r ( 1999 ) 3 -( 1 ′, 1 ′- dimethylbutyl )- 1 - deoxy - 8 - thc and related compounds : synthesis of selective ligands for the cb 2 receptor . bioorg med chem 7 : 2905 - 2914 . huffman j w , yu s , showalter v , abood m e , wiley j l , compton d r , martin b r , bramblett r d , reggio p h ( 1996 ) synthesis and pharmacology of a very potent cannabinoid lacking a phenolic hydroxyl with high affinity for the cb2 receptor . j med chem 39 : 3875 - 3877 . little p j , compton d r , johnson m r , melvin l s , martin b r ( 1988 ) pharmacology and stereoselectivity of structurally novel cannabinoids in mice . j pharmacol exp ther 247 : 1046 - 1051 . mahadevan a , siegal c , martin b r , abood m e , beletskaya i , razdan r k ( 2000 ) novel cannabinol probes for cb1 and cb2 cannabinoid receptors . j med chem 43 : 3778 - 3785 . munro s . thomas k l , abu - shaar m ( 1993 ) molecular characterization of a peripheral receptor for cannabinoids . nature 365 : 61 - 65 . reggio p h , wang t , brown a e , fleming d n , seltzman h h , griffin g , pertwee r g , compton d r , abood m e , martin b r ( 1997 ) importance of the c - 1 substituent in classical cannabinoids to cb 2 receptor selectivity : synthesis and characterization of a series of o , 2 - propano - 8 - tetrahydrocannabinol analogs . j med chem 40 : 3312 - 3318 . rinaldi - carmona m , barth f , heaulme m , shire d , calandra b , congy c , martinez s . maruani j , neliat g , caput d , ferrara p , soubrie p , breliere j c , le fur g ( 1994 ) sr 141716a , a potent and selective antagonist of the brain cannabinoid receptor . febs lett 350 : 240 - 244 . ross r a , brockie h c , stevenson l a , murphy v l , templeton f , makriyannis a , pertwee r g ( 1999 ) agonist - inverse agonist characterization at cb 1 and cb 2 cannabinoid receptors of l759633 , l759656 and am630 . br j pharmacol 126 : 665 - 672 . ryan w j , banner w k , wiley j l , martin b r , razdan r k ( 1997 ) potent anandamide analogs : the effect of changing the length and branching of the end pentyl chain . j med chem 40 : 3617 - 3625 . seltzman h h , fleming d n , thomas b f , gilliam a f , mccallion d s , pertwee r g , compton d r , martin b r ( 1997 ) synthesis and pharmacological comparison of dimethylheptyl and pentyl anandamide analogs . j med chem 40 : 3626 - 3634 . sheskin t , hanu_l , slager j , vogel z , mechoulam r ( 1997 ) structural requirements for binding of anandamide - type compounds to the brain cannabinoid receptor . j med chem 40 : 659 - 667 . sheskin t , hanu_l , slager j , vogel z , mechoulam r ( 1997 ) structural requirements for binding of anandamide - type compounds to the brain cannabinoid receptor . j med chem 40 : 659 - 667 showalter v m , compton d r , martin b r , abood m e ( 1996 ) evaluation of binding in a transfected cell line expressing a peripheral cannabinoid receptor ( cb2 ): identification of cannabinoid receptor subtype selective ligands . j pharmacol exp ther 278 : 989 - 999 . song z h , bonner t i ( 1996 ) a lysine residue of the cannabinoid receptor is critical for receptor recognition by several agonists but not win - 55 , 212 . mol pharmacol 49 : 891 - 896 . thomas b f , adams i b , mascarella w , martin b r , razdan r k ( 1996 ) structure - activity analysis of anandamide analogs : relationship to a cannabinoid pharmacophore . j med chem 39 : 471 - 479 . wiley j l , compton d r , dai d , lainton j a h , phillips m , huffman j w , martin b r ( 1998 ) structure - activity relationships of indole and pyrrole - derived cannabinoids . j pharmacol exp ther 285 : 995 - 1004 . the disclosures of all of the above - cited references are incorporated herein by reference . the k i &# 39 ; s are presented as means ± sem . all ed 50 &# 39 ; s are expressed as μmol / kg ( with 95 % confidence limits in parentheses ). for compounds that failed to produce either maximal or dose - related effects , the percent effect at the highest dose ( mg / kg : in parenthesis ) is provided . sa = suppression of spontaneous activity : mpe = % maximum possible intinociceptive effect in tail flick assay : rt = rectal temperature . * this dose ( μmol / kg ) produced & gt ; 50 % inhibition and was the lowest dose tested . the k i &# 39 ; s are presented as means ± sem . all ed 50 &# 39 ; s are expressed as μmol / kg ( with 95 % confidence limits in parentheses ). for compounds that failed to produce either maximal or dose - related effects , the percent effect at the highest dose ( mg / kg : in parenthesis ) is provided . sa = suppression of spontaneous activity ; mpe = % maximum possible antinociceptive