Secologanin aglycone

Although not an alkaloid, condoxine (146) is a compound of considerable interest, and it is relevant to include it here. In contrast to dihydrosecologanin aglycone, which condenses with 2-oxotryptamine with the formation of the oxin-dole analogue (147) of dihydromancunine, secologanin aglycone reacts with 2-oxotryptamine to produce an oxindole base, condoxine, of structure (146).84 Condoxine is thus obtained by cyclization of Nb and the prospective C-7 in... 

T 4.68, and a double doublet (/ = 8,5 Hz) at t 4.88, which moved downfield to t 4.00 on acetylation, attributed to protons at C-1 and C-5 respectively], which also eflfectively excluded the possible structures (96) and (97). TTie aglycones (94) and (95) are almost certainly formed by an intramolecular displacement, as shown in (98) the alternative mechanism proceeds via the ring-opened dialdehyde, which would be expected to produce at least some (96) or (97). Further, the acyclic aldehyde from secologanin aglycone would almost certainly isomerize to the conjugated aldehyde the retention of the double bond in the terminal position therefore implies that ring a remains intact. 

Brown s original synthesis of dihydromancunine (99) started with Nb-benzyldihydrovincoside and employed conditions that bore little resemblance to likely in vivo processes. However, experience with the secologanin aglycone (see above) suggested a one-pot biomimetic synthesis of dihydromancunine and indeed,... 

The [2 -t- 2] photoannelation of 1 to 1,4-cyclohexadiene (5) is the key step in a recent synthesis of secologanin aglycone O-methyl ether (7). In both cases the photoproducts possess the c/s-ring junction. ... 

The cleavage reaction was used for a synthesis of secoiridoids for example, secologanin aglycone O-methyl ether (6) was obtained by fragmentation of (5) in respectable yield. ... 

When the aldehyde partner of the Pictet-Spengler reaction with tryptamine is the terpene secologanin, strictosidine is formed as an entry toward the vast monoterpene indole alkaloids [32, 33]. Hydrolysis of the glucosidic part releases the strictosidine aglycone bearing an aldehyde, while imin-ium formation and further cyclization and reduction can lead to ajmalicine (from oxocyclization) or yohimbine (from car-bocyclization). These alkaloids are referred to as from the Corynanthe type, with the monoterpene carbon skeleton unmodified. Although it misses one carbon and has a very... 

---