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 synthesized^3,4—the DL, cis and trans, 9-10 and 11-12, methylene octadecanoic acids. The crystal structures of two of these racemates have been studied^5,6, 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.