Synthesis of enantiopure 6,11-methylene lipoxin B4 methyl ester

Abstract

The synthesis of Lipoxin B4 analogs (LXB4) to gain access to stabilized inflammation resolving compounds is an actual field of research. Focusing on variation and stabilization of the conjugated E,Z,E,E C6–C13 tetraene moiety of natural LXB4, a methylene bridge introduced between C6 and C11 suppresses any Z/E isomerization of the C8–C9 olefin. Intending to enable prospective structure variations in connection with the C1–C5 and C14–C20 fragments, a convergent total synthesis has been developed. Optically active C1–C12 building blocks were build-up from cycloheptatriene 1-carbonester (C6–C11, C21) and glutaryl chloride (C1–C5) using Friedel-Crafts-type acylation and chiral HPLC. The C13–C20 segment had been generated via a five-step sequence starting from heptanoyl chloride. Horner key olefination enabled the assembly of the carbon backbone. A final five-step sequence including a chelate Cram reduction of the unsaturated ketone moiety afforded the target 6,11-methylene LXB4 methyl ester.