(E)-(HYDROXYIMINO)(HYDROXYMETHOXYPHOSPHINYL)ACETIC ACID - SYNTHESIS AND PH-DEPENDENT FRAGMENTATION

In contrast to both its parent ''troika'' acid (E-l, a phosphorylating agent at pH 7 and 25 degrees C) and its C-methyl isomer (E-2, which i s stable at both acidic and neutral pH), (E)-(hydroxyimino)(hydroxymet hoxyphosphinyl)acetic acid E-3 was unreactive at pH 7 and 25 degrees C but at pH 1.5 fragmented to methyl phosphate 10 (15%) and methyl phos phorocyanidate 11 (85%). The minor product is consistent with Solvent phosphorylation, the reaction exclusively observed with E-l. The non-p hosphorylating fragmentation pathway is proposed to involve a prelimin ary E --> Z isomerization of 3 prior to C-alpha-C-beta cleavage. Dual fragmentation pathways were also detected (P-31 NMR) when the DCHA(+) salt of E-3 (E-9) was heated in acetonitrile or EtOH; in addition to p hosphorylation products (16-19%), 11 was Termed (81-84%). Reaction of E-9 in refluxing EtOH:t-BuOH (1:1) showed low stereoselectivity in pro duct formation (similar to 3:1 ethyl methyl phosphate:I-butyl methyl p hosphate), supporting a dissociative phosphorylation process.