Abstract

Four new alkaloids, comprising three 3-oxo-3,7-seco-oxindole alkaloids (hirsutanine D–F, 1–3) and one oxindole alkaloid N-oxide (uncarine B N-oxide, 4), together with four known heteroyohimbine-type oxindole alkaloids, were isolated from the stems of Uncaria hirsuta Havil. Structures of 1–4 were elucidated by extensive NMR and HR-ESIMS data analyses. Compound 3 is the first 3-oxo-3,7-seco-oxindole alkaloid with ring B opened and degraded isolated from the Uncaria genus. Compounds 1–3 exhibited slight inhibition effect on the proliferation of the breast cancer cell MDA-MB-231. The positive mode collision-induced dissociation of the 3-oxo-3,7-seco-oxindole alkaloids (1–3) was featured by the β-cleavage and α-cleavage of the amido bond, while the N-oxide (4) showed characteristic neutral eliminations of ·OH and H2O.

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