Diethyl phosphorocyanidate hydrolysis

S)-2 are obtained by N-acylation using diethyl phosphorocyanidate (DEPC) (ref. 5), followed by hydrolysis. The results are summarized as follows. 

Konieczny, M.T., Toma, PH., and Cushman, M., Synthesis of hydroxyethylene isosteres of the transition state of the HIV protease-catalyzed Phe-Pro hydrolysis. Reaction of 2-[(Boc)amino]-l-(2 -oxocyclopentyl)-3-phenylpropanols with diethyl phosphorocyanidate and lithium cyanide followed by samarium iodide, J. Org. Chem., 58, 4619, 1993. 

A synthesis of MTX y-hydrazide (VIII.224) was described in 1981 by Rosowsky et al. [299], Condensation of MeAPA with y-methyl a-/-butyl L-glu-tamate with the aid of diethyl phosphorocyanidate afforded the diester (VIII.225) (76% yield), which was then converted sequentially to (VIII.226) (60% yield) on treatment with hydrazine in MeOH solution at 4 °C for 3 days and to (VIII.224) (45% yield) on hydrolysis with 1 M HCl at 50 °C for 1 h. Compound (VIII.224) has gained attention recently because of the opportunity it affords to couple MTX to monoclonal antitumour antibodies through the formation of semicarbazide bonds to periodate-oxidized sugars [331]. The y-hydrazide derivative (VIII.227) of AMT has also been cited briefly [332], although details of its synthesis have not yet been disclosed. 

The MTX y-peptide (VIII.239), in which the y-carboxyl is joined to 4-ami-nobutyric acid, has been synthesized [352] as a de(carboxy) analogue of MTX -I- G,. Condensation of a-benzyl L-glutamate with MeAPA by the diethyl phosphorocyanidate procedure gave a 94% yield of a-benzyl MTX, which on reaction with methyl 4-aminobutyrate in the presence of diphenylphosphoryl azide and subsequent ester hydrolysis with Ba(OH)2 was converted to (VIII.239) in 50% overall yield. 

Another peptide derivative of MTX was prepared [362] with the aim of covalently attaching it to antibodies. Condensation of oxidized glutathione tetraethyl ester with 4-amino-4-deoxy-A °-methylpteroic acid with the aid of diethyl phosphorocyanidate afforded the tetraethyl ester (VIII.262) (47% yield). Hydrolysis of the ester groups with Ba(OH)2 followed by ion-exchange chromatography in the presence of 2-mercaptoethanol gave a crude product which was assumed to be the reduced tripeptide. On further purification by gel filtration without 2-mercaptoethanol, this compound underwent spontaneous oxidation to disulphide (VIII.263). In a model experiment, an IgG, monoclonal antibody directed against human transferrin receptor was activated by reaction with A-succinimidyl-3-(2-pyridyldithio)propionate, and con-... 

B. 0. Holmstead has carried out investigations on the rate of hydrolysis of cyano-phosphorus compounds. First of all, mention may be made of the hydrolysis of diethyl phosphorocyanidate which proceeds rapidly in a buffer solution at pH 7-2 giving rise to the CN ion. Some 90 per cent hydrolysis takes place at this pH in 1 hr. Under similar conditions tabun is also hydrolysed to cyanide to the extent of about 80 per cent in 12 hr. There is a concurrent diminution of toxicity as the hydrolysis proceeds. Even in distilled water 50 per cent of the cyanide is split off in 9 hr. This instability would seem to render this compound in-effective as a toxic agent for use on a large scale. 

---