Alkaloids corynanthe

B. CORYNANTHE ALKALOIDS 1. Antirhine and Antirhine jVb-Metho Salts... 

Dihydrocorynantheol (21), first isolated from Aspidosperma marcgravianum (147), is the simplest corynanthe alkaloid. The members of this type of alkaloid have three stereo centers in the D ring of the indolo[2,3-a]quinolizine skeleton. This substitution pattern allows four possible relative arrangements for the C-3, C-15, and C-20 stereo centers, the names of which are normal, pseudo, alio, and epiallo, respectively. 

An interesting transformation was discovered by Sakai and Shinma (181) during the chemical investigation of corynanthe alkaloid (V-oxides. Polonovski reaction and sodium cyanoborohydride reduction of hirsuteine A-oxide (331) gave corynantheine (52) and 3-isocorynantheidine (65), the latter likely formed by reduction of the conjugated iminium intermediate 334. 

L-tyrosine Tyrosine-derived alkaloids Indole alkaloids Quinoline alkaloids /3-carboline alkaloids Pyrroloindole alkaloids Ergot alkaloids Iboga alkaloids Corynanthe alkaloids Aspidosperma alkaloids Protoalkaloids Terpenoid indole alkaloids True alkaloids... 

Alkaloids like preakuammicine (Figure 6.79) and akuammicine (Figure 6.75) contain the C10 and C9 Corynanthe type terpenoid units respectively. They are, however, representatives of a subgroup of Corynanthe alkaloids termed the Strychnos type because of their structural similarity to many of the alkaloids found in Strychnos... 

The analogous photocyclisation of enamides is well known and is of particular value in synthesis. Photocyclisation of the enamides (29) to the furopyridones (30), for example, has been used in the preparation of key intermediates for alkaloid synthesis. Similar approaches have been employed in the synthesis of corynanthe alkaloids ° and in the preparation of trans-hexahydro-indolo[43-ab]phenanthridines as selective dopamine agonists. The benzoylmethylenebenzothiazepines (31) can be converted in the same way into the B-homo-5-thiaprotoberberines (32). Enamide photocyclisation has also been employed in the syntheses of halo-benzofuro[2,3-c]quinolines,benzo[h][l]- and benzo[/j[1]-benzo-... 

Averaged values from three different Corynanthe alkaloids. 

Sakai and Shinma were interested in the chemical correlation of the Corynanthe alkaloids with those of the C-mavacurine type and have carried out a number of successful transformations in this area (189,190). 

However, very recently in a series of biomimetic experiments it has been established that under virtually physiological conditions vincoside is transformed into akuammigine (140b) and strictosidine into tetrahydroalstonine (139b) and ajmalicine i.e. the precursor for the 3a Corynanthe alkaloids was the 3a glycoalkaloid and hence no inversion at C-3 was required (73). Concurrent biosynthetic work on V. rosea it was found that strictosidine was... 

Quite recently Zenk and co-workers have shown that strictosidine is also a biological precursor for terpenoid indole alkaloids of 3fl configuration. The biosynthetic conversion proceeds with loss of hydrogen at C-3, while it is retained in the formation of 3 a, Corynanthe alkaloids (107). 

The Corynanthe alkaloids represented by ajmalicine 6.243) and tetrahydroalstonine (6.260) are the simplest variations of the stric-... 

Wanner, M. J., Claveau, E., van Maarseveen, J. H., Hiemstra, H. (2011). Enantioselec-tive syntheses of corynanthe alkaloids by chiral Br0nsted acid and palladium catalysis. Chemistry - A European Journal, 17, 13680-13683. 

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