Abstract
AbstractThree spermidine alkaloids – oncinotine (1), neooncinotine (3), and isooncinotine (2) – have been isolated from the stem bark of Oncinotis nitida BENTH. (Scheme 1); 1 and 3 are so far an unseparable mixture. However, by treatment of this mixture with K‐t‐butoxide, neooncinotine is completely converted into isooncinotine, and oncinotine, the main alkaloid, is obtained in pure form.The structural assigment of these alkaloids is based on chemical and spectral evidence. Thus oncinotine (1) has been degraded via 24 (Scheme 4) and 32 to the putrescine derivative 35 and the piperidine derivative 34 (Scheme 5). Similarly neooncinotine (3) and isooncinotine (2), have given 34 along with the 1, 3‐diaminopropane derivative 36 (Scheme 5). The major decomposition pathways of 24, 35 and 36 in the mass spectra are described in Schemes 8, 6 and 7 respectively. The absolute configuration of 1, 2 and 3 is derived by chiroptical correlations with (R)‐(−)‐N‐methylconiine (38).
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