From Aspidosperma excelsum, rootbark, which has previously been shown to exhibit antimicrobial activity, 6 antimicrobial active alkaloids were isolated and identified: il-methoxytubotaiwine, ochrolifuanine A, tetrahydrosecamine, 16-demethoxycarbonyltetrahydrosecamine, 16-hydroxytetrahydrosecamine and 1 6-hydroxy, 16-demethoxycarbonyltetrahydrosecamine. The minimum inhibitory concentration was determined for some of the alkaloids, using Bacillus subtilis as test organism. Didemethoxycarbonyltetrahydrosecamine was also shown to exhibit antimicrobial activity. No activity against gram negative bacteria could be found for the alkaloids by means of biograms. The site of demethoxycarbonylation in demethoxycarbonyltetrahydrosecamine was established as C-16. The structures of the two new Secamine type alkaloids, 16-hydroxytetrahydrosecamine and 16-hydroxy, 1 6-demethoxycarbonyltetrahydrosecamine were determined by means of their spectral data. During the isolation of the antimicrobially active alkaloids some inactive alkaloids were also isolated: compactinervine, N-acetylaspidospermidine, 0-dimethylaspidospermine, aricine, yohimbine and 0-acetylyohimbine.

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