Volumen 48, Fasciculus 5 (1965) -No. 119 LITERATURVERZEICHNI S I ) Auszug itus der Diss. E. ISELI, Hasel 1963. 2, 30. Mitt. vgl. E. ISELI ct al. [l].

Natural Vincamine (1) has been synthesized in an enantioselective manner starting from the ethylpentenal 7. In the key step a mixture of the diastereoisomeric racemates, 14 and 15, was directly obtained from the silyl enol ether 11 and the dihydro‐β‐carboline 12 by the way of an intramolecular Mannich reaction of the intermediate 13 (Scheme 4). The undesired stereoisomers, 14 and 15b, were recycled to 15a using the related reversible Mannich reaction 18 ⇄ 14 + 15, followed by crystallization of the salt from 15a and (+)malic acid. 15a was converted to natural vincamine (1) in several steps including the known transformation 20→1.

The syntheses of the alkaloids of the ergotoxine-group z.e. ergocristine, aand bergokryptine, and ergocornine, are described. Using starting material with known stereochemistry these syntheses allowed to determine the absolute configurations also a t C-2' and C-12' in the peptide part, which could not be derived from analytical data. All crgot alkaloids of the peptide type possess t h c same stereochemical structure.Die Peptid-Mutterkornalkaloide Ergocristin, aund p-Ergokryptin und Ergocornin werden unter der Bezeichnung Ergotoxin-Gruppe zusammengefasst, weil ein isomorph kristallisierendes Gemisch dieser Alkaloide fruher fur ein einheitliches Alkaloid gehalten und als ((Ergotoxin)) bezeiclinet worden war [2] 131. Diese Alkaloide bilden auch in cheniiscli-struktureller Hinsiclit eine Gruppe, indeni sie in ihrem Peptidteil den gleichen a-Hydroxy-a-amino-saure-Baustein, namlich das a-Hydroxy-L-valin, enthalten und sich dadurch von den Alkaloiden der Ergotamin-Gruppe, denen das a-Hydroxy-L-alanin gemeinsain ist, und vom Ergostin, das als Bindeglied zwischen Lysergsaure-Rest und Peptidteil a-Hydroxy-L-a-aminobuttersaure aufweist, unterscheiden. (Vgl. allgemeine Formel A).

Addition reactions on the alicyclic double bond of eburnamenine and apovincamine SummaryThe addition of alcohols, amines or thiols on the 14,15-double bond of (-)eburnamenine (3a) or ( + )-apovincamine (9a) yielded the corresponding analogues of vincanol (5b-h), epivincanol(7b-d), vincamine (lob-e) and epivincamine (1 lb-g) with varying stereoselectivity. The reaction was achieved by addition of hydrogenbromide at -78" followed by nucleophilic attack, or in the (-)-eburnamenine series also by direct addition of alcohols and thiols under acidic conditions. Without exception the analogues of epivincamine (1 la-g) exhibited two carbonyl absorption bands in their IR. spectra. (-)-Eburnamenine (3a) was obtained from (+ )-apovincamine (9a) in a simple one pot reaction.Einleitung. -Die Alkaloide Eburnamin (6) aus Hunteria eburnea PICHON [ 11 und Vincamin (10a) aus Vinca minor L. [2] sind die Prototypen der nach ihnen benannten Indolalkaloid-Klasse Eburnamin-Vincamin [3]. Die Alkaloide dieser Klasse sind Derivate von Ringgeriisten gleicher Konstitution, namlich des 13 a-Athyl-2,3,5,6,12,13,13a, 13b-octahydro-1 H-indolo [3,2,l-de]pyrido[3,2,1-ij] [ 1, Slnaphtyridins, gelegentlich auch im ersteren Fall ccEburnan)> (2) [ 11, im letzteren ctVincan))