Stereoselective detoxification of chiral sarin and soman analogues by phosphotriesterase.

The catalytic activity of the bacterial phosphotriesterase (PTE) toward a series of chiral analogues of the chemical warfare agents sarin and soman was measured. Chemical procedures were developed for the chiral syntheses of the S(P)- and R(P)-enantiomers of O-isopropyl p-nitrophenyl methylphosphonate (sarin analogue) in high enantiomeric excess. The R(P)-enantiomer of the sarin analogue (k(cat)=2600 s(-1)) was the preferred substrate for the wild-type PTE relative to the corresponding S(P)-enantiomer (k(cat)=290 s(-1)). The observed stereoselectivity was reversed using the PTE mutant, I106A/F132A/H254Y where the k(cat) values for the R(P)- and S(P)-enantiomers were 410 and 4200 s(-1), respectively. A chemo-enzymatic procedure was developed for the chiral synthesis of the four stereoisomers of O-pinacolyl p-nitrophenyl methylphosphonate (soman analogue) with high diastereomeric excess. The R(P)R(C)-stereoisomer of the soman analogue was the preferred substrate for PTE. The k(cat) values for the soman analogues were measured as follows: R(P)R(C,) 48 s(-1); R(P)S(C), 4.8 s(-1); S(P)R(C), 0.3 s(-1), and S(P)S(C), 0.04 s(-1). With the I106A/F132A/H254Y mutant of PTE the stereoselectivity toward the chiral phosphorus center was reversed. With the triple mutant the k(cat) values for the soman analogues were found to be as follows: R(P)R(C,) 0.3 s(-1); R(P)S(C), 0.3 s(-1); S(P)R(C), 11s(-1), and S(P)S(C), 2.1 s(-1). Prior investigations have demonstrated that the S(P)-enantiomers of sarin and soman are significantly more toxic than the R(P)-enantiomers. This investigation has demonstrated that mutants of the wild-type PTE can be readily constructed with enhanced catalytic activities toward the most toxic stereoisomers of sarin and soman.

Boric acid converts urine into an effective bacteriostatic transport medium.

Results of an experiment designed to assess the usefulness of boric acid for preserving urine before its bacteriological examination are reported. Boric acid at a concentration of 20 g/l was found to be usefully bacteriostatic, largely eliminating the false positive results obtained with unpreserved specimens when delay before culture was more than 90 min. The effect lasted for up to 48 h. There was no evidence that borate is toxic to the urinary pathogens encountered in naturally infected urine. Borate also preserves white blood cells in urine and thereby marginally improved the diagnosis of pyuria. The results confirm that boric acid may with benefit be added to bottles used for transporting specimens of urine to the laboratory.