Structure of Malvalic Acid and Some Related C18 and C19 Cyclopropane Fatty Acids

Abstract

IN recent years an interesting group of fatty acids containing a cyclopropane or a cyclopropene ring has been isolated from natural products or synthesized. This work followed the discovery by Hofmann et al. 1,2 of a biologically active C19H36O2 cyclopropane fatty acid, lactobacillic acid, in the lipides of Lactobacillus arabinosus and L. casei. Four more C19 acids of this type were synthesized3,4—the DL, cis and trans, 9-10 and 11-12, methylene octadecanoic acids. The crystal structures of two of these racemates have been studied5,6, namely, the DL trans 9-10 and DL cis 11-12, and shown to have the characteristic straight- and bent-chain configurations illustrated in the electron density Fourier projections in Figs. 1 and 2. From the similarity in the diffraction data, the other two racemates are believed to be structurally isomorphous7 in the trans and cis series, respectively. Of these, the DL cis 9-10 acid was shown7 to be identical with the dihydrosterculic acid obtained4 by hydrogenation of the sterculic acid8, C19H34O2, from the kernel oil of the tropical tree Sterculia foetida.