Corynanthe alkaloids synthesis

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-... 

Pictet-Spengler isoquinoline synthesis. The final steps in a synthesis of (—)-antirhine (2), a Corynanthe-type indole alkaloid, involved partial reduction of the lactam 1 to a hemiamina), which cyclizes to 2 in the presence of dilute HC1,2... 

The absolute configuration of 1 was established in 1967.4 Since then, l5 and 2a6 have been the subject of several syntheses. A challenge in both cases was the stereochemistry at the three stereogenic centers of the quinolizidine subunit. Tietze and co-workers have previously synthesized indole alkaloids of the corynanthe group,7 this problem is based on the recent enantioselective total synthesis of 1.2,8,12... 

Ajmalicine, 19-epi-ajmalicine and tetrahydroalstonine are formed from 4,21-dehydrogeissoschizine via cathenamine (Fig. 2.9). The enzymatic synthesis of these corynanthe-type alkaloids has been investigated using C. roseus cell suspension cultures, and the enzymes involved have been reviewed by De Luca (1993) and Ziegler and Facchini (2008). Ajmalicine can be oxidized by POD to serpentine. This reaction may take in the vacuole. 

The asymmetric synthesis of 6-lactone 8, a key intermediate for (-)-antirhine (a Corynanthe-type indole alkaloid)998 from optically pure alcohol 5a (>99% Z) involves such a type of Cope rearrangement969. The anionic oxy-Cope rearrangement of 6a under the standard conditions yields the erythro-yxoduct 7a with 80% de and 84% ee. 

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