Application and microbial preparation of D-valine

D-Valine is an important organic chiral source and has extensive industrial application, which is used as intermediate for the synthesis of agricultural pesticides, semi-synthetic veterinary antibiotics and pharmaceutical drugs. Its derivatives have shown great activity in clinical use, such as penicillamine for the treatment of immune-deficiency diseases, and actinomycin D for antitumor therapy. Fluvalinate, a pyrethroid pesticide made from D-valine, is a broad-spectrum insecticide with low mammalian toxicity. Valnemulin, a semi-synthetic pleuromutilin derivative synthesized from D-valine, is an antibiotic for animals. Moreover, D-valine is also used in cell culture for selectively inhibiting fibroblasts proliferation. Due to its widespread application, D-valine is gaining more and more attention and some approaches for D-valine preparation have been investigated. In comparison with other approaches, microbial preparation of D-valine is more competitive and promising because of its high stereo selectivity, mild reaction conditions and environmental friendly process. So far, microbial preparation of D-valine can be mainly classified into three categories: microbial asymmetric degradation of DL-valine, microbial stereoselective hydrolysis of N-acyl-DL-valine by D-aminoacylase, and microbial specific hydrolysis of DL-5-isopropylhydantoin by D-hydantoinase coupled with D-carbamoylase. In this paper, the industrial application of D-valine and its microbial preparation are reviewed.

D-(−)-2-Azaniumyl-2-(4-hydroxyphenyl)acetate: an orthorhombic polymorph

The title compound, C8H9NO3, is the zwitterionic form of D-(−)-4-hydroxyphenylglycine. The plane of the hydroxybenzene ring is inclined at an angle of 88.89 (5)° to the best-fit plane through the five non-H atoms of the aminoacetate substituent. In the crystal, N—H...O and O—H...O hydrogen bonds link adjacent molecules, forming a three-dimensional network. Weak C—H...π interactions are also observed.

Isolation and characterization of L-valine-degrading Candida maltosa DLPU-zpb for D-valine preparation from DL-valine

To develop a practical process for D-valine preparation from DL-valine, L-valine was used as a sole source of carbon and nitrogen in basal minimal medium to isolate L-valine-degrading micro-organisms. A yeast strain DLPU-zpb was obtained, which showed asymmetric degrading activity against DL-valine. Based on the morphology, physiological and biochemical characteristics, and 26S rDNA D1/D2 domain sequence, strain DLPU-zpb was identified as Candida maltosa. The cells of this strain were used as a biocatalyst for eliminating the L-isomer from DL-valine. The L-isomer was completely degraded within 72 h under the conditions of 30°C, pH control at 6·0, 200 rev min(-1) and 50 g l(-1) DL-valine. The strain DLPU-zpb degraded L-valine effectively but not D-valine, and thus D-valine could be easily isolated from the resultant reaction mixture, which provides a new method for D-valine preparation from DL-valine.

SIGNIFICANCE AND IMPACT OF THE STUDY

D-valine is an important raw material for medicines and its demand is increasing year by year. Several approaches for D-valine preparation have been reported, but none of them are likely to provide product at low cost. A newly isolated L-valine-degrading yeast strain Candida maltosa DLPU-zpb was described, which showed asymmetric degrading activity against DL-valine. Thus, a new and practical process for D-valine preparation from DL-valine could be developed. This is the first report of the asymmetric degrading ability of C. maltosa against DL-valine and D-valine preparation from DL-valine.