Abstract
Five corynomycolic acids [2-alkyl-3-hydroxyfatty acid : CmH2m+1CH (OH) CH (CnH2m+1) COOH] with alkyl chain length (total carbon numbers, 12, 16, 20, 24, and 28) were synthesized and the relation between chemical structure and surface active properties was determined. The unitary acids were synthesized in three steps from ethyl alkanoates with carbon numbers of 6, 8, 10, 12, and 14 as the starting material, respectively : (1) Claisen ester condensation of ethyl alkanoate, (2) selective reduction of C=O to OH by NaBH4, and (3) hydrolysis of hydroxy ester under alkaline conditions.
Surface tension and interfacial tension toward the decane of aqueous alkaline solution of synthetic corynomycolic acid decreased with increase in its concentration and a well-defined critical micelle concentration (cmc) was not evident in the case of corynomycolic acid from microorganisms was observed. With increase in the length of the alkyl chain, the values of surface and interfacial tension at cmc decreased and became less than that of synthetic surfactants for corynomycolic acid carbon numbers exceeding 16. The surface-active properties of synthetic corynomycolic acid were inferior to those of the corresponding 3-hydroxyfatty acid [Cm+nH2m+2n+1+CH (OH) CH2COOH] but superior to those of 3-hydroxyfatty acid whose carboxylic alkyl chain was of the same length [CmH2m+1CH (OH) CH2COOH].
