BrRD20 improves abiotic stress resistance in chrysanthemum.

RESPONSIVE TO DESSICATION 20 (RD20) is a member of the caleosin family, which is involved in plant growth and development, signal transduction, abiotic stress and plant immunity. However, the molecular mechanism of the biological function of RD20 in turnip is still largely unknown. This study aimed to characterise the roles of BrRD20 during abiotic stress resistance and their responses in various abiotic stresses by isolating BrRD20 (MK896873) from 'Tsuda' turnip. Quantitative polymerase chain reaction analysis showed that the highest expression levels of BrRD20 occurred in the petal, followed by the leaf, bud and red root epidermis, with tissue specificity. The transcript level of BrRD20 was much higher under natural light than under dark conditions in 0-5-day-old turnip seedlings. BrRD20 was also induced to be regulated by abiotic stresses such as high or low temperature, dehydration, osmotic hormone salt and alkali stresses. BrRD20 overexpression (BrRD20 -OE) in Chrysanthemum presented an enhanced tolerance to low temperature, dehydration and salt stress compared with the wild type. The BrRD20 gene was induced to be regulated by abiotic stresses such as high or low temperature, dehydration, osmotic and salt stresses. The BrRD20 gene also improved abiotic stress resistance in chrysanthemum. The above results suggested that BrRD20 plays a crucial role in abiotic stress resistance.

Novel macrocyclic HCV NS3 protease inhibitors derived from α-amino cyclic boronates.

A novel series of P2-P4 macrocyclic HCV NS3/4A protease inhibitors with α-amino cyclic boronates as warheads at the P1 site was designed and synthesized. When compared to their linear analogs, these macrocyclic inhibitors exhibited a remarkable improvement in cell-based replicon activities, with compounds 9a and 9e reaching sub-micromolar potency in replicon assay. The SAR around α-amino cyclic boronates clearly established the influence of ring size, chirality and of the substitution pattern. Furthermore, X-ray structure of the co-crystal of inhibitor 9a and NS3 protease revealed that Ser-139 in the enzyme active site traps boron in the warhead region of 9a, thus establishing its mode of action.

Synthesis and evaluation of novel alpha-amino cyclic boronates as inhibitors of HCV NS3 protease.

We have designed and synthesized a novel series of alpha-amino cyclic boronates and incorporated them successfully in several acyclic templates at the P1 position. These compounds are inhibitors of the HCV NS3 serine protease, and structural studies show that they inhibit the NS3 protease by trapping the Ser-139 hydroxyl group in the active site. Synthetic methodologies and SARs of this series of compounds are described.

Investigations of valanimycin biosynthesis: elucidation of the role of seryl-tRNA.

The antibiotic valanimycin is a naturally occurring azoxy compound produced by Streptomyces viridifaciens MG456-hF10. Precursor incorporation experiments showed that valanimycin is derived from l-valine and l-serine via the intermediacy of isobutylamine and isobutylhydroxylamine. Enzymatic and genetic investigations led to the cloning and sequencing of the valanimycin biosynthetic gene cluster, which was found to contain 14 genes. A novel feature of the valanimycin biosynthetic gene cluster is the presence of a gene (vlmL) that encodes a class II seryl-tRNA synthetase. Previous studies suggested that the role of this enzyme is to provide seryl-tRNA for the valanimycin biosynthetic pathway. Here, we report the results of investigations to elucidate the role of seryl-tRNA in valanimycin biosynthesis. A combination of enzymatic and chemical studies has revealed that the VlmA protein encoded by the valanimycin biosynthetic gene cluster catalyzes the transfer of the seryl residue from seryl-tRNA to the hydroxyl group of isobutylhydroxylamine to produce the ester O-seryl-isobutylhydroxylamine. These findings provide an example of the involvement of an aminoacyl-tRNA in an antibiotic biosynthetic pathway.

General synthesis of pyrroloquinolizidines: synthesis of an unnatural homologue of the pyrroloindolizidine myrmicarin alkaloid 215B.

A general synthesis approach to pyrroloquinolizidines (3,4,5,5a,6,7,8-heptahydropyrrolo[2,1,5-de]quinolizines) via a münchnone 1,3-dipolar cycloaddition is reported. The approach was applied to the synthesis of an unnatural pyrroloquinolizidine homologue of myrmicarin 215B.