Evaluation of derivatives of 3-(2-oxo-1-pyrrolidine) hexahydro-1H-azepine-2-one as dermal penetration enhancers: side chain length variation and molecular modeling

The present study examined the enhancement effect of two series of compound s derived from 3-(2-oxo-1-pyrrolidine)hex ahydro-1H-azepine-2-one. One seri es possessed alkyl side chains (series I) and the other alkyl ester side ch ains (series II). An in vitro diffusion study was performed to investigate the effect of variation in alkyl/alkyl ester side chain length of two serie s of compounds on the permeation of hydrocortisone (HC) across hairless mou se skin. The permeability coefficient (P), 24 h receptor concentration (Q,, ) and skin content (SC), as well as the enhancement ratios (ER) for each pa rameter were recorded, A parabolic relationship was observed between the ER ,, and the alkyl side chain length of the enhancers. The relationship betwe en the length of ester side chains and ER, appeared to be relatively linear with R-2 of 0.9676. The relationship between the calculated lipophilicity (CL) and enhancement activity of the enhancers showed that for CL 5-9, seri es I showed higher P values compared with Azone((R)), but this was not obse rved with series II. For CL values 4.57-7.75, a significant correlation exi sted between P of HC and CL of series II compounds (R-2 = 0.9967). 1-Tetrad ecyl-3-( 2-oxo-1-pyrrolidine)-epsilon -caprolactam showed the highest P and Q(24), with 40.5- and 18.6-fold increases over the control. In conclusion. the alkyl side chain series of compounds showed more enhancing activity th an the alkyl eater side chain series. (C) 2001 Published by Elsevier Scienc e B.V.