Isolation and structure elucidation of novel hypotensive agents, niazinin A, niazinin B, niazimicin and niaziminin A+ B from Moringa oleifera: the first naturally occurring thiocarbamates - Faizi, S; Siddiqui, B S; Saleem, R; Siddiqui, S; Aftab, K (J Chem Soc [Perkin I], 1992)