Antirhine, structure

Antirhine (1) is the major alkaloid of Antirhea jutaminosa, having a tra 5-3a-H,15 3-H structure with a cis CfD ring junction. A synthesis of 1 has been achieved starting with... 

There is considerable confusion in the older literature regarding the naming of this plant. It has been placed at various times in the genera Antirrhoea, Timonius, and GvMtareUa. The major alkaloid is antirhine, C19H24ON2 (mp 112°-114° [a]u —2°) whose structure is XIII. Its dihydro derivative melts at 106°-108° ([a]jj -(-23°) 17). 

When these stereochemical results were applied to vincoside, the indolic analog of deacetylipecoside and its C-3 epimer, strictosidine, which had been correlated chemically with corynantheine and antirhine (Section IV,A), conflicting results were obtained. They cast serious doubt on the validity of the previous assignment and indicated that inversion of C-5 must have occurred at some stage in the chemical operations. An independent X-ray crystallographic study of 0,0-dimethylipecoside was therefore undertaken. The results obtained confirmed in detail the structure and absolute stereochemistry derived chemically, except that the hydrogen atom at C-5 should have a (i configuration (13). 

Antirhine (C19H24N2O, mp 112-114°, [ajj, —2° (CHCI3)), has been isolated from Antirrheaputaminosa (F. v. Muell.) Bail, and the structure CXXIII has been proposed for it (61). Vinca herbacea yielded hervine (C23H28N2O4, mp 173-175°, [a]p —93° (EtOH)) for which the structure CXXIV has been assigned (62). 

At about the same time, Coune et al. (336) independently reported the isolation from roots of the African S. gossweileri Exell and structure determination of strychnoxanthine (15b), which is now seen to be the 14-oxo derivative of the curare alkaloid. The two substances belong to a group of compounds having the rather unusual H(15) J -configuration, the occurrence of which is explained by their presumed biosynthesis from antirhine (16) or vallesiachotamine (17) through an additional cyclization between C(17) and C(18) (336, 475). The presence of the latter base has not yet been demonstrated in South American Strychnos species. 

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