Useful Syntheses of (3<i>S</i>)-2,3,4,5-Tetrahydropyridazine-3-carboxylic Acid and Its Dehydrotetrapeptide Derivatives
作者:Yutaka Nakamura、Chung-gi Shin
DOI:10.1246/cl.1991.1953
日期:1991.11
The stereoselective synthesis of (3S)-2,3,4,5-tetrahydropyridazine-3-carboxylic acid (Pya), which is a cyclic α-amino acid at center of antrimycins (1), was successful. Moreover, the synthesis of the C-terminal dehydrotetrapeptide of 1 containing Pya residue at N-terminus is described.
(3S)-2,3,4,5-四氢哒嗪-3-羧酸 (Pya) 的立体选择性合成是成功的,它是一种位于抗霉素 (1) 中心的环状 α-氨基酸。此外,还描述了在 N 端含有 Pya 残基的 1 的 C 端脱氢四肽的合成。
Tandem Action of the O<sub>2</sub>- and FADH<sub>2</sub>-Dependent Halogenases KtzQ and KtzR Produce 6,7-Dichlorotryptophan for Kutzneride Assembly
作者:John R. Heemstra、Christopher T. Walsh
DOI:10.1021/ja806467a
日期:2008.10.29
Kutznerides are actinomycete-derived antifungal nonribosomal hexadepsipeptides which are assembled from five unsual nonproteinogenic amino acids and one hydroxy acid. Conserved in all structurally characterized kutznerides is a dichlorinated tricyclic hexahydropyrroloindole postulated to be derived from 6,7-dichlorotryptophan. In this Communication, we identify KtzQ and KtzR as tandem acting FADH(2)-dependent halogenases that work sequentially on free L-tryptophan to generate 6,7-dichloro-L-tryptophan. Kinetic characterization of these two enzymes has shown that KtzQ (along with the flavin reductase KtzS) acts first to chlorinate at the 7-position of L-tryptophan. KtZR, with a similar to 120 fold preference for 7-chloro-L-tryptophan over L-tryptophan, then installs the second chlorine at the 6-position of 7-chloro-L-tryptophan to generate 6,7-dichloro-L-tryptophan. These findings provide further insights into the enzymatic logic of carbon-chloride bond formation during the biosynthesis of halogenated secondary metabolites.