Non-enzymic coupling of vindoline and catharanthine to synthesize 3′,4′-anhydrovinblastine under irradiation with near-ultraviolet light

Triarylaminium Radical Cation Promoted Coupling of Catharanthine with Vindoline: Diastereospecific Synthesis of Anhydrovinblastine and Reaction Scope

A new triarylaminium radical cation promoted coupling of catharanthine with vindoline is disclosed, enlisting tris(4-bromophenyl)aminium hexachlororantimonate (BAHA, 1.1 equiv) in aqueous 0.05 N HCl/trifluoroethanol (1-10:1) at room temperature (25 °C), that provides anhydrovinblastine in superb yield (85%) with complete control of the newly formed quaternary C16' stereochemistry. A definition of the scope of aromatic substrates that participate with catharanthine in the BAHA-mediated diastereoselective coupling reaction and simplified indole substrates other than catharanthine that participate in the reaction are disclosed that identify the key structural features required for participation in the reaction, providing a generalized indole functionalization reaction that bears little structural relationship to catharanthine or vindoline.

Optimization of 3', 4'-Anhydrovinblastine Synthesis in vitro Using Crude Extracts of Catharanthus roseus Irradiated with Near-Ultraviolet Light

Dimeric indole alkaloids (DIAs), such as vinblastine and vincristine, found in Catharanthus roseus are used clinically as antitumor drugs. A stable supply of DIAs is desired because these alkaloids are very expensive due to their low abundance in plants. A coupling reaction between catharanthine (CAT) and vindoline (VID) is the rate-limiting step of DIAs biosynthesis in planta. 3', 4'-Anhydrovinblastine (AVLB), the product of the coupling reaction, is the precursor of CAT and VID. Therefore, an effective AVLB production system is greatly required. Previously we found that the coupling reaction of CAT and VID to produce AVLB occurred in the presence of flavin mononucleotide and manganese ion (II) by irradiation with near-ultraviolet light at a peak of 370 nm without the presence of any enzyme. In this study, we investigated the effects of organic solvents on this non-enzymatic reaction. We show that the addition of 10% methanol to the reaction mixture permitted the preparation of a highly concentrated substrate solution, resulting in a high yield of AVLB by the coupling reaction. Conditions for the coupling reaction in 10% methanol solution were optimized. We also confirmed that the coupling reaction could occur in crude extracts of C. roseus obtained by organic solvent extraction. These findings suggest a method to produce DIAs on a large scale with reduced production costs.

A Review on Recent Developments in Syntheses of the post-Secodine Indole Alkaloids. Part II: Modified Alkaloid Types

The second part of the planned review on developments in the field of total and formal total synthesis of the post-secodine indole alkaloids concentrates on modified alkaloid types, i.e. those skeletons derived from primary types by formation of additional and/or rupture of existing bonds, while connectivities next to indol(e)ine moiety remain intact. It thus reviews the synthesis of alkaloids of quebrachamine/cleavamine type including VLB-bis-indoles, rhazinilam type, aspidofractinine/kopsane and kopsifoline type, as well as kopsijasminilam alkaloids, lapidilectine B and danuphylline. It covers the literature of from 1991-1992 up to approximately end 2006. A review with 174 references.

Catharanthine oxidation in flavin mononucleotide-mediated catharanthine-vindoline coupling reaction for synthesis of dimeric indole alkaloids under near-ultraviolet light

A reaction model for the flavin mononucleotide-mediated coupling of catharanthine (C) and vindoline (V) under near-ultraviolet light was established based on the results of experiments on the effects of various physical and chemical factors on the disappearance of C and V, and the synthesis of the product, a dihydropyridinium intermediate (IM). The following events were deduced to occur. (i) C is oxidized in the presence of FMN and oxygen under near-ultraviolet light (C(OX1)). (ii) C(OX1) then couples with V to form IM. Degradation of C occurs simultaneously with its specific oxidation, as a result of which a part of the C is converted into the product (C*) which is incapable of coupling with V. When a reaction in which C(OX1) is further oxidized to another form (C(OX2)) is added and the counterpart for the coupling with V is changed to C(OX2) from C(OX1), the reaction model more appropriately describes the exponential increase in the product, IM, that occurs in the early stage of the coupling reaction. (iii) The degradation rate of IM is much greater after C has been consumed than before its disappearance. Using this reaction model, the coupling reactions under basal and optimized conditions were simulated and the results showed a good fit with the experimental values under both conditions. The kinetic study suggests that manganese ion (Mn2+) stimulates the binding of C(OX2) with V in addition to suppressing the degradation of C, resulting in an increased yield of IM. Mn2+ thus appears to be an important factor in the coupling reaction, in which it plays two different roles.