{HEAD ~ R27} is alkyl of 1 6 carbon atoms, arylalkyl of 7 10 carbon atoms, allyl, fluorenylmethyl, or {TAIL ~ phenyl} which is optionally mono , di , or tri substituted with a substituent selected from alkyl of 1 6 carbon atoms, alkoxy of 1 6 carbon atoms, hydroxy, cyano, halo, nitro, carbalkoxy of 2 7 carbon atoms, trifluoromethyl, amino or CO2 H 
{ HEAD ~ R27 } is alkyl of 1 6 carbon atoms , arylalkyl of 7 10 carbon atoms , allyl , fluorenylmethyl , or { TAIL ~ phenyl } which is optionally mono , di , or tri substituted with a substituent selected from alkyl of 1 6 carbon atoms , alkoxy of 1 6 carbon atoms , hydroxy , cyano , halo , nitro , carbalkoxy of 2 7 carbon atoms , trifluoromethyl , amino or CO2 H
HEAD HEAD HEAD HEAD HEAD REL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH