Greenwaylactams A, B and C, the First Group of Sesquiterpene Alkaloids with an Eight‐Membered Lactam Ring from Greenwayodendron oliveri. Issue 7 (16th February 2021) - Kemgni, Mireille F.
Abstract: Three new sesquiterpene alkaloids of the polyveoline type containing eight‐membered lactam rings named greenwaylactam A (1 ), B (2 ) and C (3 ) were isolated from the leaves of a Cameroonian medicinal plant Greenwayodendron oliveri (Engl.) Verdc along with three known compounds diacetylpolyveoline (4 ), N ‐acetyl‐8α‐polyveolinone (5 ) and methyl pheophorbide‐A (6 ). These comprise the first members of a new class of ξ‐lactam sesquiterpenes. Compounds were isolated by means of successive column chromatographies and their structures were elucidated by extensive NMR spectroscopic analyses and HRESIMS. The configuration of 1 was deduced from its single‐crystal X‐ray diffraction. The crude extract and some isolated compounds were assessed for their antibacterial activity against four enteric bacterial strains Escherichia coli, Salmonelles typhi, Shigella dysenterie and Klebseilla pneumonie using the micro‐dilution method. Compounds 1, 2, 5 and 6 were the most active with MIC values varying between 31.25–250 μg/mL. Abstract : New sequiterpene alkaloid analogues with unusual skeletons were isolated from the leaves of Greenwayodendron oliveri . These comprise the first members of a new class of ξ‐lactam sesquiterpenes. The isolated compounds displayed antibacterial activity against the tested enteric bacterial strains with greenwaylactam B (2 ) being the most active on E. coli (31.25 μg/mL). The plausible biosynthetic pathway for these compounds and the single crystal X‐ray diffraction analysis of greenwaylactam A (1 ) are also discussed.