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.

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.

At present, physicochemical properties of amino acid molecular crystals are of the utmost interest. The compounds where molecules have different chirality are the focus of particular interest. This paper, presents a study on the structural and electronic properties of crystalline L- and DL-valine within the framework of density functional theory including van der Waals interactions. The results of this study showed that electronic properties of the two forms of valine are similar at zero pressure. Pressure leads to different responses in these crystals which is manifested as various deformations of molecules. The pressure effect on the infrared spectra and distribution of electron density of L- and DL-valine has been studied.