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Synthesis of enantiomerically pure indoloquinolizine derivatives

✍ Scribed by Shiqi, Peng ;Li, Zhang ;Mengshen, Cai ;Winterfeldt, Ekkehard

Publisher
John Wiley and Sons
Year
1993
Tongue
English
Weight
612 KB
Volume
1993
Category
Article
ISSN
0947-3440

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✦ Synopsis

Abstract

L‐Tryptophan methyl ester reacts with 1,1,3,3‐tetramethoxypropane to give methyl carbolinecarboxylate 2 as a 1:2 mixture of the (1__R__,3__S__) and (1__S__,3__S__) stereoisomers. Conversion to the corresponding amides (1__R__,3__S__)‐3 and (1__S__,3__S__)‐3 was accomplished by treatment of 2 with ammonia. Benzylation of (1__R__,3__S__)‐3 or (1__S__,3__S__)‐3 afforded the corresponding 2‐benzylcarbolineamide (1__R__,3__S__)‐4 or (1__S__,3__S__)‐4. Dehydration of the amide group in (1__R__,3__S__)‐4 or (1__S__,3__S__)‐4 yielded the corresponding 2‐benzylcarbolinenitrile (1__R__,3__S__)‐5 or (1__S__,3__S__)‐5, which was treated with NaBH~4~ to reductively remove the cyano group. Hydrogenation removed the benzyl‐protectin group of 6 resulting in (1__R__)‐7 or (1__S__)‐7, which is then alkylated with methyl vinyl ketone to give the Michael adduct (1__R__)‐8 or (1__S__)‐8. Subsequent Aldol reaction and dehydration afforded the enantiomerically pure indoloquinolizine derivatives (12b__R__)‐9 or (12b__S__)‐9, which was shown to be enantiomerically pure by recording their ^1^H‐NMR spectra in the presence of a chiral shift reagent.

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