The chemical nature of amavadin

Abstract

807leaves little doubt that the acylated phenylisoserine side chain of these taxoids is synthesized via path a of Scheme I. Unexpectedly, in both experiments 1, but not 2, also showed a pronounced M + 10 peak, as well as a P + 10 satellite for the m / z 286 fragment representing the side chain. Hence, the aromatic ring of 4a and Sa must have also becn incorporated into the benzoyl group of the 1 side chain. Together with the non-incorporation of 7a this suggests the operation of a new pathway, other than the estab-lishedI3 path b/c of Scheme I, for the genesis of the benzoate moieties in this plant which proceeds from 3 via 4 (path a/d) or 4 and S (path a/e).In summary, the side chain of 1 and 2 is formed from phenylalanine via @-phenylalanine, presumably generated by an aminomutase reaction,14 followed by hydroxylation of C-2 and acylation of the nitrogen. The benzoyl moiety is also formed via @-phenylalanine and possibly phenylisoserine rather than via cinnamic acid. A&"t .We are indebted to Prof.

Crystal Structure of the VV Dimer [V2O2(μ‐O)(dmpp)2(OCH3)2] and Its Equilibrium with the VV Trimer [V3O3(μ‐O)3(dmpp)3(H2O)](H2O)2 in Methanol/Water Solutions

“…This assignment is corroborated by the observation of 51 V high frequency shifts of the signals for the dimer with respect to those of the monomer in other systems, such as the oxovanadium alkoxides VO(OR) 3 or vanadate complexes of hydroxy acids such as glycerate or lactate. [30] In a highly concentrated methanol solution, this compound precipitates as red crystals, which were analysed by X-ray crystallography.…”

“…[1,2] It is present in some biological systems in high concentrations, where it seems to have a relevant role, such as in the Amanita muscaria mushroom as the amavadin complex [3] and in some ascideas in the form of tunichromes. [4] Vanadium is the cofactor of some enzymes, like the vanadium-dependent haloperoxidases in al-3586 of the V 2 Y 2 L 2 and V 1 Y signals decrease sharply, and a broad signal at -488 ppm appears, corresponding to the original V V trimer complex, which is the only species present in 94 % water.…”

Synthesis, structural characterization and electrochemical activity of oxidovanadium(IV/V) complexes of a diprotic ONS chelating ligand

“…The tridentate ONS ligand forms one six membered and one five membered chelate ring at the vanadium(V) acceptor center, the corresponding bite angles being 82.31°(9) and 80.58° (11), respectively the two axial positions are occupied by the oxido oxygen atom O35 and nitrogen atom N23 of the secondary ligand bipyridine. The short V1-O35 distance of 1.595(3) Å indicate the presence of vanadium oxygen double bond commonly found in five and six coordinated complexes of V(IV) and V(V).…”

Study on the isomerism in meso-amavadin and an amavadin analogue

“…3 Furthermore, the vanadium atom is configurationally labile in solution and the complex is prone to epimerization [18,23,24]. The interconversion between D and K diastereomers occurs via a flip of one of the N-O moieties (Fig.…”

“…5a) [18,23]. It has previously been shown that only minimal structural changes take place upon the one-electron oxidation to vanadium(V) when the amavadin ligand 1 [7,24] In 'meso-amavadin' the situation appeared to be more complicated because the presence of (R) and (S) stereogenic centers in the ligands breaks the symmetry of the molecule. This results in eight different possibilities to arrange the two meso-ligands around the vanadium, instead of the two possibilities for the (S,S)-ligands.…”