Thiophosphorane intermediates

An enzyme that catalyses ATP-dependent 2 -phosphorylation and acetyl-CoA-dependent 6 -acetylation of the antibacterial aminoglycosides has been reported.260 Because of its complementary spectrum of two enzymic reactions, this bifunctional enzyme has a wide breadth of activity. Pentacoordinated thiophosphorane intermediates such as (292a) and (292b) are involved in the hydrolytic reactions of the monothioate analogues of 5 -O-methyluridine 2 - and 3 -dhnethylphosphates, (293) and (294), which have been studied over a wide range of HC1 acidities, //<, = —1.7 to pH9.261... 

The alkaline hydrolysis of isopropyl, 2-ethoxyethyl, 2,2-dichloroethyl, and 2,2,2-trichloroethyl uridine 3 -thiomonophosphates (86a-d), similar to a series of aryl analogues (86e) studied previously, proceeded via a transient pentacoordinated dianionic thiophosphorane intermediate (87) to yield, via the formation and ring-opening of a 2, 3 -cyclic thiophosphate (88), a mixture of 2 - and 3 -thiophosphates, (89) and (90) (Scheme 24). For the alkyl esters (86a-d), the breakdown of the thiophosphorane intermediate (87) was rate determining, but for the aryl esters (86e), which have better leaving groups, its formation was rate determining. " ... 

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