the following paragraphs provide definitions of various chemical moieties and terms , and are intended to apply uniformly throughout the specification and claims unless an otherwise expressly set out definition provides a different definition . the term “ peptide ” is ordinarily applied to a polypeptidic chain containing from 3 to 30 or more contiguous amino acids , usually from 3 to 20 contiguous amino acids . such peptides can be generated by methods known to those skilled in the art including partial proteolytic cleavage of a larger protein , chemical synthesis , or genetic engineering . the expression “ derivative or analogue ” means any compound the chemical structure of which contains modifications with respect to the parent peptide , but which maintains at least 50 %, more preferably at least 75 %, most preferably at least 90 % of the biological activity of a compound of formula i . the term “ derivatives ” as herein used refers to derivatives which can be prepared from the functional groups present on the lateral chains of the amino acid moieties or on the n -/ or c - terminal groups according to known methods . such derivatives include for example esters or aliphatic amides of the carboxyl - groups and n - acyl derivatives of free amino groups or o - acyl derivatives of free hydroxyl - groups and are formed with acyl - groups as for example alcanoyl - or aroyl - groups . the term “ salts ” herein refers to both salts of carboxyl groups and to acid addition salts of amino groups of the peptides , polypeptides , or analogs thereof , of the present invention salts of a carboxyl group may be formed by means known in the art and include inorganic salts , for example , sodium , calcium , ammonium , ferric or zinc salts , and the like , and salts with organic bases as those formed , for example , with amines , such as triethanolamine , arginine or lysine , piperidine , procaine and the like . acid addition salts include , for example , salts with mineral acids such as , for example , hydrochloric acid or sulfuric acid , and salts with organic acids such as , for example , acetic acid or oxalic acid . any of such salts should have substantially similar activity to the peptides and polypeptides of the invention or their analogs . “ c 1 - c 6 - alkyl ” refers to monovalent alkyl groups having 1 to 6 carbon atoms . this term is exemplified by groups such as methyl , ethyl , n - propyl , isopropyl , n - butyl , isobutyl , tert - butyl , n - hexyl and the like . by analogy c 1 - c 5 - alkyl refers to monovalent alkyl groups having 1 to 5 carbon atoms . “ c 1 - c 6 acyl ” refers to a group — c ( o ) r where r includes h and “ c 1 - c 5 - alkyl ” groups . this term includes formyl (— c ( o ) h ) and acetyl (— c ( o ) ch 3 ). “ amino ” refers to the group — nrr ′ where each r , r ′ is independently hydrogen or “ c 1 - c 6 - alkyl ”. “ amidated amino acid ” refers to an amino acid wherein the hydroxy group from the acid moiety has been replaced by an amino group . “ acylated amino acid ” refers to an amino acid wherein the one hydrogen atom on tie nitrogen has been replaced by a c 1 - c 6 acyl group . further , an “ acetylated amino acid ” refers to an amino acid wherein the one hydrogen atom on the nitrogen has been replaced by an acetyl group . “ substituted ” refers to groups substituted with from 1 to 5 substituents selected from the group comprising “ c 1 - c 6 - alkyl ”, “ amino ”, “ halogen ”, trihalomethyl , cyano , hydroxy , mercapto , nitro , and the like . the polypeptides and the peptides of the present invention can be in other alternative forms which can be preferred according to the desired method of use and / or production , is for example as active fractions , precursors , salts , derivatives , conjugates or complexes . compounds of the invention are suitable for the treatment and / or prevention of a diabetic condition , including a disease associated with abnormal folding of the islet amyloid polypeptide , type i or type ii diabetes and postransplantation type i or type ii diabetes . the compounds of the invention may be prepared by any well - known procedure in the art , including chemical synthesis technologies . examples of chemical synthesis technologies are solid phase synthesis and liquid phase synthesis . as a solid phase synthesis , for example , the amino acid corresponding to the c - terminus of the peptide to be synthesized is bound to a support which is insoluble in organic solvents , and by alternate repetition of reactions , one wherein amino acids with their amino groups and side chain functional groups protected with appropriate protective groups are condensed one by one in order from the c - terminus to the n - terminus , and one where the amino acids bound to the resin or the protective group of the amino groups of the peptides are released , the peptide chain is thus extended in this manner . solid phase synthesis methods are largely classified by the tboc method and the fmoc method , depending on the type of protective group used . typically used protective group include tboc ( t - butoxycarbonyl ), cl - z ( 2 - chlorobenzyloxycarbonyl ), br - z ( 2 - bromobenzyloxycabonyl ), bzl ( benzyl ), fmoc ( 9 - fluorenylmethoxycarbonyl ), mbh ( 4 , 4 ′- dimethoxydibenzhydryl ), mtr ( 4 - methoxy - 2 , 3 , 6 - trimethylbenzenesulphonyl ), trt ( trityl ), tos ( tosyl ), z ( benzyloxycarbonyl ) and cl 2 - bzl ( 2 , 6 - dichlorobenzyl ) for the amino groups ; no 2 ( nitro ) and pmc ( 2 , 2 , 5 , 7 , 8 - pentamethylchromane - 6 - sulphonyl ) for the guanidino groups ); and tbu ( t - butyl ) for the hydroxyl groups ). after synthesis of the desired peptide , it is subjected to the de - protection reaction and cut out from the solid support . such peptide cutting reaction may be carried with hydrogen fluoride or tri - fluoromethane sulfonic acid for the boc method , and with tfa for the fmoc method . the present invention provides compounds capable of controlling iapp aggregation and fibril formation the activity of the compound of the invention in inhibiting the amylin fibrils can be detected using , for example , an in vitro assay , such as that described by klunk et al ., 1999 and fezou et al ., 1999 , which measures the ability of compounds of the invention to prevent the aggregation of the islet amyloid polypeptide ( iapp ). results are reported in the examples . amylin fibrils are cytotoxic , inducing cell death by apoptosis ( lorenzo et al ., 1994 ). compounds of the invention can be tested for their ability to prevent cytotoxicity of amylin fibrils . results are reported in the examples . in one embodiment , the invention provides compounds according to formula i , wherein x 1 is selected from aspartic acid and acetylated aspartic acid . in another embodiment , the invention provides compounds according to formula i , wherein x 2 is selected from leucine and amidated leucine . in another embodiment , the invention provides compounds according to formula i , wherein x 3 is absent . in another embodiment , the invention provides compounds according to formula i , wherein x 1 is aspartic acid and x 2 is leucine . in another embodiment , the invention provides compounds according to formula i , wherein x 1 is acetylated aspartic acid and x 2 is amidated leucine . in another embodiment , peptides of the invention are of following formula ii : wherein r 1 is selected from h , optionally substituted c 2 - c 6 acyl and optionally substituted c 1 - c 6 alkyl preferably h and acetyl ; r 2 is selected from oh and nr 3 r 4 , wherein r 3 and r 4 are independently selected from h and optionally substituted c 1 - c 6 alkyl , preferably r 2 is selected from oh and nh 2 ; r 5 , r 6 , r 7 , r 8 and r 9 are independently selected from h and c 1 - c 6 alkyl . in another embodiment , peptides of the invention are of following formula iii : wherein r 1 is selected from h , optionally substituted c 2 - c 6 acyl and optionally substituted c 1 - c 6 alkyl , preferably h and acetyl and r 2 is selected from oh and nr 3 r 4 , wherein r 3 and r 4 are independently selected from h and optionally substituted c 1 - c 6 alkyl preferably r 2 is selected from oh and nh 2 ; r 5 , r6 , r 7 and r 8 are independently selected from h and c 1 - c 6 alkyl . in another embodiment , the invention provides compounds according to formulae ii or iii , wherein r 5 , r 6 , r 7 and r 8 are h . in another embodiment , the invention provides compounds according to formulae ii or iii , wherein r 1 is h and r 2 is oh . in another embodiment , the invention provides compounds according to formulae ii or iii , wherein r 1 is acetyl . in another embodiment , the invention provides compounds according to formulae ii or iii , wherein r 2 is nh 2 . in another embodiment , the invention provides compounds according to formula iii wherein r 1 is acetyl and r 2 is nh 2 . in another embodiment of the invention , peptides of formula i are selected from the group consisting of seq id no . 2 , seq id no . 3 and . seq id no . 4 . in another embodiment of the invention , peptides of formula i can be used for the preparation of a medicament for the treatment or prevention of iapp related disorders such as diabetes type i or type ii , e . g . to prevent or delay the aggregation of amylin associated with the onset and / or progression of type ii diabetes or for the treatment of islet cells , e . g . cultured pancreatic islet cells in vitro prior to their transplantation , for the treatment of type i diabetes patients , e . g ., post - transplantation , to prevent or inhibit fibril formation in the transplanted cells . still another embodiment of the present invention , is a method for treating or preventing an iapp related amyloidosis , such as a diabetic disorder , preferably type ii diabetes or post - transplantation type i diabetes . a further embodiment of the invention is a method for treating or preventing iapp disorders wherein the method comprises administering an effective dose of the above - mentioned peptides and derivatives thereof to a subject in the need thereof , wherein the subject can be human or animal , preferably human . a further embodiment of the invention comprises the administration of at least a compound of the invention in a regimen coordinated with insulin or with glucose sensitizers , e . g . in a treatment for diabetes for simultaneous , sequential or separate use . pharmaceutical compositions comprising at least one peptide of the invention include all compositions wherein the peptide ( s ) are contained in an amount effective to achieve the intended purpose . in addition , the pharmaceutical compositions may contain suitable pharmaceutically acceptable carriers comprising excipients and auxiliaries which facilitate processing of the active compounds into preparations which can be used pharmaceutically . suitable pharmaceutically acceptable vehicles are well known in the art and are described for example in gennaro et al , 2000 , a standard reference text in this field . pharmaceutically acceptable vehicles can be routinely selected in accordance with the mode of administration , solubility and stability of the peptides . for example , formulations for intravenous administration may include sterile aqueous solutions which may also contain buffers , diluents and other suitable additives . the use of biomaterials and other polymers for drug delivery , as well the different techniques and models to validate a specific mode of administration , are disclosed in literature ( luo et al ., 2001 and cleland et al ., 2001 ). the above - mentioned peptides and derivatives of the present invention may be administered by any means that achieve the intended purpose . for example , administration may be achieved by a number of different routes including , but not limited to subcutaneous , intravenous , intradermal , intramuscular , intraperitoneal , intracerebral , intrathecal , intranasal , oral , rectal , transdermal , intranasal or buccal . preferably the compounds of the invention are administered by subcutaneous , intramuscular or intravenous injection or infusion . parenteral administration can be by bolus injection or by gradual perfusion over time . a typical regimen for preventing , suppressing , or treating amylin misfolding related disorders , comprises either ( 1 ) administration of an effective amount in one or two doses of a high concentration of inhibitory peptides in the range of 0 . 5 to 10 mg of peptide , more preferably 0 . 5 to 5 mg of peptide , or ( 2 ) administration of an effective amount of the peptide in multiple doses of lower concentrations of inhibitor peptides in the range of 10 - 1000 μg , more preferably 50 - 500 μg over a period of time up to and including several months to several years . it is understood that the dosage administered will be dependent upon the age , sex , health , and weight of the recipient , concurrent treatment , if any , frequency of treatment , and the nature of the effect desired . the total dose required for each treatment may be administered by multiple doses or in a single dose . preparations for parenteral administration include sterile aqueous or non - aqueous solutions , suspensions , and emulsions , which may contain auxiliary agents or excipients which are known in the art . suitable formulations for parenteral administration include aqueous solutions of the active compounds in water - soluble form , for example , water - soluble salts . in addition , suspension of the active compound as appropriate oily injections suspensions may be administered . depending on the intended route of delivery , the compounds may be formulated as injectable or oral compositions . the compositions for oral administration can take the form of bulk liquid solutions or suspensions , or bulk powders . more commonly , however , the compositions are presented in unit dosage forms to facilitate accurate dosing . the term “ unit dosage forms ” refers to physically discrete units suitable as unitary dosages for human subjects and other mammals , each unit containing a pre - determined quantity of active material calculated to produce the desired therapeutic effect , in association with a suitable pharmaceutical excipient . typical unit dosage forms include pre - filled , pre - measured ampoules or syringes of the liquid compositions or pills , tablets , capsules , or the like in the case of solid compositions . in such compositions , the compound of the invention is usually a minor component ( from about 0 . 1 to about 50 % by weight or preferably from about 1 to about 40 % by weight ) with the remainder being various vehicles or carriers and processing aids helpful for forming the desired dosing form . liquid forms suitable for oral administration may include a suitable aqueous or non - aqueous vehicle with buffers , suspending and dispensing agents , colorants , flavours and the like . solid forms may include , for example , any of the following ingredients , or compounds of a similar nature : a binder such as microcrystalline cellulose , gum tragacanth or gelatine ; an excipient such as starch or lactose ; a disintegrating agent such as alginic acid , primogel , or corn starch ; a lubricant such as magnesium stearate ; a glidant such as colloidal silicon dioxide ; a sweetening agent such as sucrose or saccharin ; or a flavouring agent such as peppermint , methyl salicylata , or orange flavouring . injectable compositions are typically based upon injectable sterile saline or phosphate - buffered saline or other injectable carriers known in the art . the above - described components for orally administered or injectable compositions are merely representative . further materials as well as processing techniques and the like are known to the skilled practitioner ( gennaro et al ., 2000 ). the compounds of this invention can also be administered in sustained release forms or from sustained release drug delivery systems . a description of representative stained release materials is also known to the skilled practitioner ( karsa et al ., 1993 and yacobi et al ., 1998 ). by “ effective amount ”, is meant an amount sufficient to achieve a concentration of peptide ( s ) which is capable of slowing down or inhibiting the formation of amylin deposits , or of dissolving pre - formed deposits . such concentrations can be routinely determined by those of skilled in the art . the amount of the compound actually administered will typically be determined by a physician , in the light of the relevant circumstances , including the condition to be treated , the chosen route of administration , the actual compound administered , the age , weight , and response of the individual patient , the severity of the patient &# 39 ; s symptoms , and the like . it will also be appreciated by those of skilled in the art that the dosage may be dependent on the stability of the administered peptide . a less stable peptide may require administration in multiple doses . the expression “ pharmaceutically acceptable ” is meant to encompass any carrier , which does not interfere with the effectiveness of the biological activity of the active ingredient and that is not toxic to the host to which is administered . for example , for parenteral administration , the above active ingredients may be formulated in unit dosage form for injection in vehicles such as saline , dextrose solution , serum albumin and ringer &# 39 ; s solution . besides the pharmaceutically acceptable carrier , the compositions of the invention can also comprise minor amounts of additives , such as stabilizers , excipients , buffers and preservatives . the present invention has been described with reference to the specific embodiments , but the content of the description comprises all modifications and substitutions , which can be brought by a person skilled in the art without ending beyond the meaning and purpose of the claims . the invention will now be described by means of the following examples , which should not be construed as in any way limiting the present invention . the examples will refer to the figures specified here below . fig1 compares sequences of human , cat , mouse , rat and hamster amylin . the amyloidogenic domain spanning residues 20 - 29 is shown by arrows and the sequence used as a template to generate β - sheet breaker peptides is highlighted in bold . fig2 shows the effect of peptide of example seq id no . 2 on amyloid cytotoxicity . soluble amylin ( 100 μm ), soluble amylin ( 100 μm )+ peptide of seq id no . 2 ( 800 μm ), and peptide of seq id no . 2 ( 800 μm ) were pre - incubated at 37 ° c . in tris buffer ph 7 . 4 for 24 h then diluted in 50 μl of culture medium before addition to rin - m5f cells , to yield final concentrations of 2 μm ( amylin ) and 16 μm ( peptide of seq id no . 2 ). data are expressed as average mtt reduction ± sd ( n = 5 ) relative to cells treated with medium alone , which was made to equal 100 %. fig3 shows the linear relationship between ic 50 of peptide of seq id no . 2 in preventing cytotoxicity in vitro and amylin concentration . aliquots of 2 . 5 , 10 , 50 and 100 μm of amylin were incubated during 24 h at 37 ° c . with different concentrations of peptide of seq id no . 2 . thereafter , the samples were diluted in cell culture medium and cytotoxicity assay performed as described in example 2 . h ( hour ), μl ( microliters ), μm ( micromolar ), mg ( milligrammes ), min ( minutes ), ml ( milliliters ), mm ( millimolar ), mtt ( 3 - 4 , 5 - dimethylthiazol - 2 - yl )- 2 , 5 - diphenyl terazolium bromide ), nm ( nanometers ), pbs ( phosphate buffered sulfate ), pm ( picomolar ), rt ( room temperature ), sds ( sodium dodecyl sulfate , tfa ( trifluoro acetic acid ). the invention will be illustrated by means of the following examples which are not to be construed as limiting the scope of the invention . the following examples illustrate preferred compounds according to formula i , and methods for determining their biological activities . synthetic human amylin ( 1 - 37 ) ( tfa salt ) and aβ 1 - 42 were synthesized in solid phase at w . m . keck foundation , yale university . amylin was not chemically reduced to make sure that the cystein bridge between amino acids 2 and 7 was formed . control peptides , and the prion protein fragment 106 - 126 were purchased from neosystem ( strausbourg ). in order to increase the solubility of amylin ( 1 - 37 ), hcl salt of amylin by dissolving 1 mg of amylin in 1 ml of 2 mm hcl solution , sonicated for 1 min at rt in an ultrasonic water bath , then lyophilized in aliquots of 0 . 2 mg and kept dry at 4a ° c . until use . inhibitor peptides were synthesized in solid phase by neosystem . peptides were purified by hplc and purity (& gt ; 95 %) evaluated by peptide sequencing and laser desorption mass spectrometry . stock solution of the peptides were prepared in water / 0 . 1 % trifluoric acid and stored lyophilized in aliquots at − 70 ° c . concentration of the stock solution was estimated by amino acid analysis . the chemical derivatization reactions were done during the synthesis by neosystem using standard procedures . the molecular weights measured by mass spectrometry are listed in table i below : table i seq id n o . mw ( g / mol ) 2 619 3 660 4 734 10 720 11 705 12 749 13 699 14 790 15 776 16 733 17 618 solubility of peptides of the invention was obtained using a qualitative assay where the peptide was dissolved in tris buffer , ph 7 . 4 at 1 , 5 , or 10 mg / ml , vortexed briefly , and then centrifuged at 16 , 000 g for 30 min . the presence of a pellet in the bottom of the tube indicates that the peptide is not soluble at the respective concentration . the data in table ii below indicate that peptides of the invention are highly soluble : table ii seq id n o . solubilty 10 & lt ; 200 μg / ml 11 & lt ; 1 mg / ml 12 2 mg / ml 4 & gt ; 10 mg / ml 3 & gt ; 10 mg / ml 2 & gt ; 10 mg / ml the activity of compounds of the invention in inhibiting the formation of aggregated amylin fibrils can be tested by absorbance changes . amyloid formation was quantitatively evaluated by measuring the amount of bound congo red ( cb ) to the fibrils using the formula below as reported ( klunk et al ., 1999 ): wherein a 541 and a 403 are the absorbances respectively at 541 and 403 nm . aliquots of amylin at a concentration of 0 . 4 mg / ml prepared in 50 mm tris - hcl , ph 7 . 4 were incubated at 37 ° c . for 48 h in the absence or presence of 1 mg / ml of the peptide of the invention . at the end of the incubation time , 125 μl of 15 μm congo rod in pbs was added to 25 μl of sample , mixed and incubated for 10 min at rt . the absorbance of the resulting solutions was then measured at 403 and 541 nm . the amount of congo red was calculated using the above formula . the amount of congo red bound to amylin fibrils in the absence of the inhibitor was set to 100 %. the data presented in table iii below indicate that peptides of the invention inhibit the formation of amylin aggregates : table iii seq id n o . % inhibition of amylin fibrils 5 ( amylin ) 0 12 20 13 16 14 8 15 10 16 24 4 39 3 47 2 43 the mechanism proposed for the implication of amylin misfolding and aggregation in the pathogenesis of type ii diabetes is by inducing islet β - cell death and thus pancreas dysfunction . the ability of compounds of the invention to prevent or reduce the formation of cytotoxic amylin fibrils ( lorenzo et al ., 1994 ) was evaluated by measuring the inhibition of amylin induced cytotoxicity in pancreatic β - cells . toxicity was measured by comparing the effects of amylin or amylin combined with peptides of the invention , on the reduction of the redox active dye , 3 -( 4 , 5 - dimethylthiazol - 2 - yl )- 2 , 5 - diphenyltetrazolium bromide ( mtt ) by pc12 cells or rin - m5f cells ( atcc ), a pancreatic beta cell line . cells were grown in rpmi - 1640 media containing 10 % foetal bovine serum , and plated onto 96 - well plates . amylin at 0 . 2 mg / ml in 50 mm tris - hcl ph 7 . 4 , in the absence or presence of 1 mg / ml of peptide of the invention , was incubated at 37 ° c . for 48 h , then diluted in 50 μl of culture media at the appropriate peptide concentration before addition to the rin - m5f cells . after overnight incubation , 10 μl of 2 . 5 mg / ml mtt was added to each well and the incubation continued for a further 3 h . cells were then solubilized in 200 μl of 20 % ( w / v ) sds in 50 % ( v / v ) n , n ′- dimethylformamide , 25 mm hcl , 2 % ( v / v ) glacial acetic acid , ph 4 . 7 , by overnight incubation at 37 ° c . levels of reduced mtt were determined by measuring the difference in absorbance at 595 and 650 nm using a microplate reader . cell viability is measured in presence of amylin alone and for a mixture of amylin and peptides of the invention . cell viability in presence of a mixture of amylin and compound of seq id no . 2 is presented in fig2 in comparison with amylin alone . the percentage of inhibition of cellular toxicity is calculated for the mixtures in comparison to cellular toxicity induced by amylin alone . percentages of inhibition of cellular toxicity are presented in table iv below for compounds of the invention : table iv % inhibition seq id n o . amylin fibrils cytotoxicity 5 ( amylin ) 0 17 19 4 33 3 43 2 40 since the concentration at which the inhibitory effect of peptides of the invention is observed depends on the concentration of amylin used , the concentration of amylin was varied and the inhibitory concentration at 50 % of the effect ( ic 50 ) of compound of seq id no . 2 was calculated . for this , aliquots of 2 . 5 , 10 , 50 and 100 μm of amylin were incubated during 24 h at 37 ° c . with different concentrations of peptide seq id no . 2 . thereafter , the samples were diluted in cell culture medium and cytotoxicity assay performed . as shown in fig3 . the ic 50 for the peptide of seq id no . 2 has a linear relationship with amylin concentration . ic 50 were found to be 1 . 5 - 2 . 7 - fold higher than amylin concentrations used in the study . considering that amylin concentration in blood has been shown to be 2 - 3 μm , we estimate that the peptide concentration in plasma in which a 50 % of activity would be reached in vivo is 4 - 6 pm . selectivity of the effect of peptides of the invention was assayed in the same assay as presented above . selectivity of peptides of the invention towards amylin was tested by measuring the ability of peptides of the invention to inhibit cellular oxicity induced by prion protein fragment ( prp 106 - 126 ) by aβ 1 - 42 peptide . peptides of the invention were not able to inhibit either cellar toxicity of prion , nor aβ fibrils . cooper g j et al . 1987 , proc . nad . acad . sci . u . s . a ., 84 : 8628 - 32 ; fezoul et al . 1999 , int j . exp . clin . invest . 7 , 166 - 178 ; gennaro et al . 2000 , of remington &# 39 ; s pharmaceutical sciences , part 8 , 20 th edition , marck publishing company , easton , pa . ; höppener j w m et al . 2000 , n . engl . j . med , 343 , 411 - 419 ; karsa et al . 1993 , ( ed ) encapsulation and controlled release ; stephenson ( editor ); springer verlag ; yacobi et al . 1998 , oral sustained release formulations : design and evaluation , eva halperin - walega ( editor ), 1st ed . edition ; pergamon press ;