Strictosidine aglycone

The following step in the biosynthesis of the TIAs consists in the deglycosylation of strictosidine by strictosidine p-glucosidase (SGD) to form the strictosidine aglycone, which is an unstable product rapidly transformed into 4,21-dehydrogeissoschizine (Scheme 4.2). SGD is a glycoprotein localized in the endoplasmic reticulum and is highly specific for strictosidine [21]. This enzyme... 

Catharanthine is synthesized via an uncharacterized pathway from strictosidine via intermediates, strictosidine aglycone, 4,21-didehydrogeissoschizine, and stemmedine [5]. 

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... 

It is reasonable to assume that the unique precursor of angustine bases is strictosidine lactam (16), the intramolecular cyclization product of strictosidine (17). The prerequisite for cyclization is the presence of a secondary amino group in the C ring of strictosidine, that is to say, the presence of a hydrogen atom on N-4. Indeed, compound 18, the AT-benzyl-substituted aglycone of strictosidine, is not subject to cyclization, but is rather in equilibrium with the open form (19) (27). Similarly, replacement of a tetrahydro-(3-carboline unit, such as one finds in strictosidine, by a P-carboline moiety inhibits the cyclization step and thus leads to tetracyclic derivatives, typical of the alkaloids of the genus Pauridiantha. 

Fig. 8.7) [3]. After the deglucosylation of strictosidine, equilibrium of the unstable aglycon intermediates leads to the formation of 4,21-dehydrogeissoschizine, the branchpoint precursor of MIAs [13]. 

---