Erythrophleum Alkaloids Containing a C-4 Carbomethoxy Group

In a separate series of experiments 7-hydroxycassanic acid was obtained from dihydrocassamic acid by the conversion of the C-4 carbomethoxy function into a methyl group and reduction of the keto group (31). The structure for cassamic acid must be XL-A and for cassamine XL-B. The stereochemistry depicted in XL follows from the 

Chapman et al. (32) also studied the isomerization of the methyl group in the diketones analogous to XXI and XXII. These authors concluded in variance with the work of Turner that the methyl at C-14 is /3 in cassamic acid and consequently in cassaic acid. This assignment was ultimately based on the isolation of XLI from the ozonolysis of 7-desoxo-cassamic acid obtained from cassamic acid by a Clemmensen reduction. The configuration of rings B and C in XLI was shown by ORD-data. 

Two Japanese workers (33) have recently synthesized XLI by reductive alkylation of the ,j8-unsaturated ketone XLII followed by esterification. The synthetic keto ester, which must have the configuration 

This alkaloid (35), CgsHsgOeN (mp 77°-78° [oc q —38°), has recently-been isolated from Eryfhrophleum guineense G. Don. The spectral properties indicate an a,jS-unsaturated ester, two additional carbonyls, and a hydroxyl group. Acid hydrolysis of erythrophleguine provided j8-dimethylaminoethanol and an acid, C21H28O5 (mp 194°-196° [a]j, -t-54° in EtOH). The formation of this acid involves the loss of 1 mole of water with the creation of an additional UV-chromophore 243 mp, 

Chapman et al. have reported somewhat earlier (32) the isolation of a dehydrocassamic from a hydrolysis of the total alkaloids of Erythro-phleum guineense to which they have more recently (36) ascribed structure XLV. This assignment is based on the isolation of 7-desoxo-cassamic acid on Clemmensen reduction, compound XLVII on NaBH4 reduction, and XLVIII from ozonolysis followed by a metal reduction— all three of which have been obtained from cassamic acid. In addition. 

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