From the rootbark of Tabemaemontann chippii a novel antimicrobially active dimeric indole alkaloid was isolated which was assigned structure 1 on the basis of spectroscopic evidence and its synthesis.
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From 250 g rootbark of Tabervlaemontana chippii (Stapf) Pichon (Apocynaceae) approximately 4 mg of a new alkaloid has been isolated which was named vobparicine. With ceric sulphate it, gave a pink-gold colour. The colour with ferric chloride perchloric acid was greyish purple upon heating. In the 1H 500 MHz 'H-NMR the most characteristic signals were 2 indolic NH, 8 aromatic protons, a doublet (I H) at 5.96 ppm, 2 quartets (I H each) at 5.41 and 5.39 ppm, 2 doublets (1 H each) at 4.49 and 4.39 ppm, 2 singlets (3 H each) at 2.61 and 2.47 ppm and 2 doublets (3 H each) at 1.68 and 1.67 ppm. Fromthesedata it could be concluded that it was a dimeric indole alkaloid with 2 unsubstituted aromatic rings, indicating a different attachment between the 2 halves than is usual for dimeric 2'. alkaloids2. The shifts for the 2 methyl singlets suggested the presence of a vobasine half, while the 2 doublets (.J=l7.5 Hz) at 4.49 and 4.39 ppm suggested the presence of an apparicine-like half. This was confirmed by comparing the spectrum with reference 300 MHz spectra of vobasinol, conodurine (vobasinyl--half) and apparicine3.
The only 3 major differences between the spectrum of vobparicine and a combination of the spectra of apparicine and vobasinyl were the presence of a doublet (J=lO.l Hz) at 5.96 ppm, the absence of 2 singlets in the 5.3 ppm region for the 2 apparicine H22 and the appearance of an extra coupling of 10.1 Hz in the signal for the vobasinyl H3'. These facts suggested structure 1 or its C22 epimer for vobparicine. The assignment of certain signals in the lH-NMR (table 1) was confirmed by some homonuclear decouping experiments, which most importantly, showed the doublet at 5.96 ppm to be coupled (J=lO.l Hz) with the assumed signal for the vobasinyl H3* at 4.53 ppm.