Total Synthesis of Varitriol, Varioxirane, and Enantiomer of the Proposed Biosynthetic Precursor
作者:Gangarajula Sudhakar、Jakka Raghavaiah
DOI:10.1021/jo4011766
日期:2013.9.6
The first stereoselective total synthesis of varioxirane was accomplished, and the proposed biosynthetic pathway was supported by converting varioxirane to (+)-varitriol. The first total synthesis of enantiomer of the proposed biosynthetic precursor, (1E,3S,4R,5E)-1-(2-(hydroxymethyl)-3-methoxyphenyl)hepta-1,5-diene-3,4-diol, was also achieved by utilizing the unreacted allylic alcohol obtained during
(2R,3S)-3-Vinylmalic acid (VM) was designed as a mechanism-based inhibitor of threo-3-isopropylmalate dehydrogenase (LPMDH), the rate-determining enzyme responsible for the penultimate step in the biosynthetic pathway of the essential amino acid L-leucine. The synthesis of VM was achieved in six steps from diethyl (R)-malate. Besides its weak activity as a substrate, VM was shown to be a mechanism-based inhibitor (K-I = 1.20 mM) for IPMDH as deduced from the time-dependent and kinetic analyses. 2-Oxo-3-pentenoate was identified as the enzyme reaction product of VM by GCMS analysis and H-1 NMR spectroscopy, but the supplemented 2-oxo-3-pentenoate was not, in contrast, inhibitive to the enzyme reaction. It seems likely from these results that an activated or nucleophilic amino acid of IPMDH by deprotonation during the ordinary enzyme reaction process participates in a strong interaction with the 2-oxo-3-pentenoate product, probably by the formation of a transient covalent bond, which in turn gives rise to inhibition of the enzyme reaction.
Ketonization of 2-hydroxy-2,4-pentadienoate by 4-oxalocrotonate tautomerase: implications for the stereochemical course and the mechanism
作者:Huiling Lian、Christian P. Whitman
DOI:10.1021/ja00071a007
日期:1993.9
4-Oxalocrotonatetautomerase (EC 5.3.2-; 4-OT), an enzyme involved in the bacterial degradation of catechol to intermediates in the Krebs cycle, catalyzes the ketonization of 2-hydroxymuconate (1) to the α,β-unsaturated ketone (E)-2-oxo-3-hexenedioate (2). Kinetic studies on 4-OT suggest that the enzyme is an isomerase and catalyzes the transformation of (E)-2-oxo-4-hexenedioate (3) to 2 through the