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, 1106A/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 RPRC-stereoisomer of the soman analogue was the preferred substrate for PTE. The ka, values for the soman analogues were measured as follows: RPRC, 48 s(-1); RPSC, 4.8 s(-1); SPRC, 0.3 s(-1), and SPSC, 0.04 s(-1). With the 1106A/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: RPRC, 0.3 s(-1); RPSC, 0.3 s(-1); SPRC, 11 s(-1), and SPSC, 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. (C) 2001 Elsevier Science Ltd. All rights reserved.