Protoberberines type

Iwasa K, Moriyasu M, Yamori T, Turuo T, Lee D-U, Wiegrebe W (2001) In Vitro Cytotoxicity of the Protoberberine-Type Alkaloids. J Nat Prod 64 896... 

Recently, Castedo et al. (137) studied enamide photocyclization for aporphine synthesis and modified Cava s procedure (135 -137) after consideration of the reaction course and structural requirement for the exclusive formation of aporphine. Castedo s group concluded that an enamide should have a forced m-stilbene geometry, in order to avoid an undesired mode of cyclization leading to protoberberine-type compounds and also to avoid a facile conversion to oxoaporphines after cyclization. 

Although the quaternary structure is assigned to the alkaloids of protoberberine type, it is of interest to note that during isolation they are frequently extracted into chloroform from either the basic or the acidic media. This phenomenon has been explained (97, 438) by the formation of a labile complex XI between the alkaloid and chloroform. 

The isolation of the alkaloids of the protoberberine type (102) and the synthesis of columbamine from berberine (101) have been reported. The synthesis of coreximine, scoulerine, and tetrahydropalmatine have been described (59, 235, 236). The synthesis of alkaloids having a protoberberine skeleton has been reviewed (374). 

Sixteen protoberberine type alkaloids reported from Aristolochia species were listed in the table 11. Occurrence of this type alkaloids were rare in Aristolochia, they were found only in four species, A. arcuata... 

Constitution. Capaurine has one phenolic hydroxyl and four methoxyl groups. That it belongs to the protoberberine type was rendered plausible by the fact that it is oxidized to a quaternary iodide with iodine in alcohol, and this iodide is reducible with zinc and acetic or hydrochloric acid to the optically inactive tetrahydro base which is identical with capauridine. Furthermore, the 0-methyl ether of capurine, melting at 152 , Hd" —254 (methanol), has five methoxyls and on racemization by successive oxidation and reduction yields capauridine 0-methyl ether, m.p. 142 . 

Mannich-reaction (for related syntheses of protoberberine type alkaloids cf. ref. 78). 

Halbsguth, C. Meissner, O. Haeberlein, H. Positive cooperation of protoberberine type 2 alkaloids from Corydalis cava on the GABA (A) binding site. Planta Med. 2003, 69, 305-309. 

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