Diphenethylpiperidine alkaloids with tracheal smooth muscle relaxation activity from Hippobroma longiflora (L.) G. Don

Abstract

Phytochemical investigations on the whole plant of Hippobroma longiflora (L.) G. Don have resulted in the isolation and elucidation of three new diphenethylpiperidine alkaloids, hippofoline A (1), hippofoline B (2), and (−)-cis-2′,2′′-diphenyllobelidiol N-oxide (5), alongside two known alkaloids, (−)-lobeline (3) and (−)-cis-2′,2′′-diphenyllobelidiol (4). The absolute configurations of alkaloids 1 and 2 were deduced based on experimental and calculated ECD data as well as biogenetic consideration, while the absolute configurations of alkaloids 3 and 4 in their free base form were confirmed by Cu Kα radiation X-ray diffraction analyses. Alkaloids 2–4 were shown to induce concentration-dependent relaxation effects on rat isolated tracheal rings that were pre-contracted with carbachol.