Transformation of indole alkaloids. VI. A novel conversion of oxindole alkaloids into indole alkaloids via indoline derivatives
| Autor: | Shin-ichiro Sakai, Etsuji Yamanaka, Naoki Saito, Yuko Suzuki |
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| Rok vydání: | 1982 |
| Předmět: | |
| Zdroj: | Chemical and Pharmaceutical Bulletin. 30:2068-2076 |
| ISSN: | 1347-5223 0009-2363 |
| DOI: | 10.1248/cpb.30.2068 |
| Popis: | Oxindole alkaloids chosen as starting materials were isopteropodine (1a) pteropodine (1b) isoformosanine (7a) and formosanine (7b). Reduction of the iminoethers prepared from the oxindole alkaloids with Et3 O^+B^-F4, with NaBH3 (OAc) or with NaBH4/SnCl4·2Et2O afforded the indoline derivatives (3a, 3b, 9a, 9b). The configuration at C7 of 3a, b was determined by NMR analysis of the N (a)-acetyl-N (b)-oxides (6a, b). The signals of H-14β were observed at high field (δ0.5-1.0) owing to the shielding effect of the aromatic ring in all A type compounds studied. Oxidative conversion of the indolines to indole alkaloids was achieved by using MnO2 or Me2SO/ (COCl)2/Et2N as oxidizing agents, and the latter reagent gave better results than the former. Tetrahydroalstonine (11) and akuammigine (12) were obtained from 3a, b, and 19-epiajmalicine (14) and 3-iso-19-epiajmalicine (15) from 9a, b. The A type compounds were more susceptible than the B type compounds to the present reduction and oxidation sequence. |
| Databáze: | OpenAIRE |
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