Catechin epimerization is an important factor affecting tea catechin compositions and thereby tea quality. However, a lack of tea germplasms with high non-epicatechins limits relative research. Here, a tea cultivar Y510 with high non-epicatechins was firstly reported and used for catechin and RNA sequencing (RNA-Seq) analysis. Results showed that the (-)-gallocatechin gallate and (+)-catechin (...

Four interesting sequoiatones stereoisomers (1-4) were isolated from a wetland soil-derived fungus Talaromyces flavus by chiral HPLC. On the basis of comprehensive NMR and mass analyses, their planar structures were elucidated as the same as that of sequoiatone B. Among them, 1 and 3 (or 2 and 4) were a pair of enantiomers, and 1 and 2 (or 3 and 4) were a pair of stereoisomers with epimerizatio...

The natural product thiopeptide antibiotic thiostrepton is shown to undergo facile epimerization at its thiazoline residue in favor of the naturally observed D-configuration, suggesting that a classical epimerase enzyme may not be involved in its biosynthesis.

Dirithromycin (3) isomerizes upon dissolution in different solvents. From X-ray analysis of V-T 108, an analogue of dirithromycin, and comparative 1H and 13C NMR, and MS data, the isomer of dirithromycin was confirmed to be the C-16-(S)-epimer. The ratio of the two epimers at equilibrium conditions was approximately 8:2 (R/S) in methanol at room temperature.

The Dess–Martin periodinane was found to be a superior oxidant for the efficient, epimerization-free synthesis of optically active N-protected -amino aldehydes from the corresponding N-protected -amino alcohols. Highly racemization-prone products, including N-Fmoc phenylglycinal and N-trifluoroacetyl -amino aldehydes, were prepared in 95% yield with 1% epimerization. © 2000 Elsevier Science Ltd...

L-Amino acids dominate the natural world almost to the exclusion of D-amino acids. However, some important D-amino acids1 have been found in biology, notably as neurotransmitters (D-serine)2 and as building blocks (D-alanine) for bacterial cell wall synthesis.3 There has been considerable interest in understanding the mechanism of the so-called “L to D conversion” of amino acids4 since enzymes ...

(3-Epimerization in the corrinoid system has recently emerged as a complicating factor in the latter stages of the total synthesis of vitamin B12 (Eschenmoser 1971; Woodward 1973). I t has also found some application in biosynthetic studies on the origin of the methyl groups in ring C (Scott, Townsend & Cushley 1973; Scott, this Discussion p. 303). This paper sets out to review briefly the (3-e...

The amino acid proline catalyzed the three- and five-component cascade olefination-Diels-Alder-epimerization and olefination-Diels-Alder-epimerization-olefination-hydrogenation reactions of readily available precursors enones 1a-i, arylaldehydes 2a-k, alkyl cyanoacetates 3a-e and Hantzsch ester 9 to furnish highly substituted prochiral 1-cyano-4-oxo-2,6-diaryl-cyclohexanecarboxylic acid alkyl e...

The epimerization of avoparcin entities is discussed in some detail. The absolute stereochemistry of avoparcin is now known since the N-methyl terminal amino acid of the aglycone has been isolated and shown to exhibit negative optical rotation and hence has the R-configuration. The same amino acid has been isolated from an epimerized solution of avoparcin and found to have positive rotation and...