Pyrrolizidine alkaloid analogues. Synthesis of 10-membered macrocyclic diesters of (±)-synthanecine A. X-Ray molecular structure of (±)-6,7-O,O-(succinyl)synthanecine A

Abstract

The first 10-membered macrocyclic diesters of (±)-synthanecine A (4) have been synthesized. Treatment of (±)-synthanecine A with succinic anhydride yielded the 6-monoester of (±)-synthanecine A, which was lactonized via its pyridine-2-thiol ester to give (±)-6,7-O,O-(succinyl) synthanecine A (5). The macrocyclic nature of this new pyrrolizidine alkaloid analogue was established by spectroscopic data and by carrying out an X-ray crystal-structure analysis on the analogue (5). The ester carbonyl groups within the macrocyclic compound (5) are antiparallel. Further examples of 10-membered [(7)-(9)] macrocyclic diesters of (±)-synthanecine A were prepared similarly using trans-2,3-dimethylsuccinic anhydride, cyclohexane-trans-1,2- dicarboxylic anhydride, and phthalic anhydride, respectively.