Stereoselective Detoxification of Chiral Sarin and Soman Analogues by Phosphotriesterase Original Research Article

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 SP- and RP-enantiomers of O-isopropyl p-nitrophenyl methylphosphonate (sarin analogue) in high enantiomeric excess. The RP-enantiomer of the sarin analogue (kcat=2600 s−1) was the preferred substrate for the wild-type PTE relative to the corresponding SP-enantiomer (kcat=290 s−1). The observed stereoselectivity was reversed using the PTE mutant, I106A/F132A/H254Y where the kcat values for the RP- and SP-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 kcat 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 I106A/F132A/H254Y mutant of PTE the stereoselectivity toward the chiral phosphorus center was reversed. With the triple mutant the kcat 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 SP-enantiomers of sarin and soman are significantly more toxic than the RP-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.