(-)-(S)-<(6S,7S,8S)-7-butyl-2-oxo-1-azaspiro<5.5>undec-8-yl> N-(1-phenylethyl)carbamate

(6S,7S,8R,9S)-7-butyl-8,9-epoxy-1-azaspiro[5.5]undecan-2-one

(2S,1'S)-2-(1'-butylbut-2'-enyl)-6-oxopiperidine-2-carboxylic acid 1-methyl ester

(1'S)-6-oxopiperidine-2-carboxylic acid 1'-methyl-hept-2'-enyl ester