Gardnerine

Gardnerine (106) has been converted into the 2-acylindole alkaloid ochropine (107) in nine conventional stages (Scheme 14).75... 

A description73 of the conversion of gardnerine into ochropine duplicates one published earlier.l4d... 

Plants of the G. multiflora group do not contain gardnerine (1) or its derivatives, which are characterized by their typical indole chromophore. The main constituent, gardneramine (4), and various accompanying alkaloids are all at the oxidation level of oxindole. As shown in Table HI, thirteen monomeric and two dimeric Gardneria alkaloids have been isolated, and most of the structures were elucidated through chemical correlation with the established structure of 4 165,166,169,172). 

The conversion of gardnerine (1) to ochropine (39), a 2-acyl indole alkaloid isolated from the stem bark of Ochrosia poweri 175. was also carried out to establish structure 39 for the latter alkaloid. The reaction sequence is shown in Scheme 10. The nitrile function of 43 was converted to the carbomethoxy grouping by methanolysis. C-D ring cleavage with BrCN gave an epimeric mixture of C-3 hydroxyls which was then subjected to Cornforth oxidation to furnish 46. Decyanation of 46 and... 

Gardneramine (4) exhibits a mild central depressive effect, while the comparable effect of gardnerine (1) is much weaker. A medium grade of acute toxicity was found for Gardneria alkaloids. Low toxicity was observed for hydroxygardnutine (3), which should be compared with that of gardnutine (2) (176) (Table IV). 

Full details have been given of the structural work d on gardnerine, gardnu-tine and 18-hydroxygardnutine. Gardnerine (87) could be converted into vobasine types as shown, for example, in Scheme 16. 

Koumidine was first obtained from the Chinese G. elegans Benth. and shown to be a C-16 epimer of normacusine B (5). The presence of an intense NOE between H-19 and H-15, together with the different C-NMR chemical shifts of C-15 and C-21 from those of gardnerine (28),... 

Gardnerine (28), one of the major indole alkaloids of Gardneria nutans 21), was converted into koumidine (1) (22). The crucial steps in this transformation are deoxygenation from the indole ring by Pd°-assisted reduction of the aryl trifiate derivative (31) and inverting the configuration of the ethylidene side chain in 32 by Pd° catalyst (Scheme 4). 

By employing the newly developed methods, humantenirine (87), a representative humantenine-type Gelsemium alkaloid, was synthesized from a sarpagine-type indole alkaloid (63). The oxindole derivative 103 prepared from gardnerine (28) was used for further transformation (Scheme 20). 

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