I n the prcsencc of a tertiary base the wcll-known acylation of primary amines with fatty acid chlorides yields 4-alkyIidene-3alkyloxetanones 10 as byproducts, which can acylate the amino compound to give the u-alkyl-&bto amide 11. This so far not observed side reaction has been detected for the first time during rlie acylation of L-cystine di-terf-butyl ester with palmitoyl chloride. howcvcr, analoguous side products may be obtained with any other amino acid ester or amino compound in general.
Synthetic lipopeptides such as tripalmitoyl-S-glyceryl-cysteinylseryl-seryl-asparaginyl-alanine are B-cell mitogens2a3) which enhance non-specific immune response. After covalent linkage of tripalmitoyl-S-glyceryl-cysteinyl-serine to antigens immunogens4' were obtained which induced antigen-specific antibody formation in uitro and in u ~u o ~, ~' .
During the development of further carrier/ Scheme 1. Structure elucidation of the side product 3 formed during the acylation of (R,R)-cystine di-tert-butyl ester (1) with palmitoyl
, chloride and structural formula of the lipoamino acids 2, 3, and 6
(5, 7, 8 see Table 1) (H -C ~S -Of B u ) ~ 1 JParn-CI, NMM (Pam-Cys-OtBu)p 2 + (a-Pam-Pam)-Cys-OtBu 3 Pam-Cys-0 tBu a) Silica gel b) Sephadex LH-20