Reaction of Phosphorylating Agents with 2-Methyl-Δ²-Oxazoline

Abstract

DEGRADATION of esteratic enzymes which have been inhibited with diisopropyl phosphorofluoridate (DFP) yields serine phosphate¹, although serine itself is completely unreactive to DFP². Kinetic and other evidence³ suggests participation of the imidazole ring of a histidine moiety in the phosphorylation reaction, although it is not known if the ring is the initial site of phosphorylation or whether it catalyses phosphorylation of the serine. Rydon⁴ has postulated that a Δ²-oxazoline is present in the enzyme which on phosphorylation yields an O-phosphoryl serine residue. This hypothesis was based on the results of Porter et al. ⁵, who showed that 2-aminoethyl phosphate could be isolated from the reaction of 2-methyl-Δ2-oxazoline (I) and DFP in aqueous solution. Since acylating agents⁶ react with I to give stable N-acyl derivatives, and since 2-aminoethyl phosphate was isolated by Porter et al. following acid hydrolysis of the product (conditions under which N → O migration of phosphoryl groups is known to occur⁷) the reaction of I with phosphorylating agents was further examined.