Ethyl acetimidate

Other reports describe the reaction of Cys-OMe with ethyl acetimidate (61JOC820 76H1687) or with oxiranecarbonitrile and potassium cyanide. In the last case thiazines are also formed (84TL4295). 

Methyl acetimidate hydrochloride, methyl glycinate hydrochloride, potassium tert-butoxide, and methyl formate were purchased from Aldrich Chemical Company, Inc., and were used without further purification. The checkers purchased methyl glycinate hydrochloride from Tokyo Chemical Industry Co. and potassium tert-butoxide and methyl formate from Kanto Chemical Co. Step A is very sensitive to moisture. Ethyl acetimidate hydrochloride is very hygroscopic. It must be dried before use in a desiccator over phosphorus pentoxide (P2O5) under reduced pressure and handled under argon. 

Ethyl acetimidate reacts specifically with free amino groups of proteins under relatively mild conditions. It penetrates cells without impairing membrane function, and labels the protein under physiological conditions. This reagent is rapidly hydrolysed by water, but the products do not interfere with the main reaction On the other hand, a sulfonated derivative of the same compound labels the outer side of the membrane and does not penetrate inside. 

This rea t is unable, unlike ethyl acetimidate, to penetrate intact cells and may therefore be used to label proteins on the outer surfaces of the membranes Methyl 3,5-di( I)iodohydroxybenzimidate... 

Amino-5-phenylpyrazole and ethyl acetimidate give the pyrazolylamidine (179). This reacts with different reagents to give derivatives of pyrazolo[l,5-a][l,3,5]triazine (Scheme 56) <74JHC69l) (c/. Section 4.05.3.2). 

Cyclization of cytidine (45a), cytosine (45c), or cytidine-5-phosphate (45d), with ethyl acetimidate gave the respective 5,6-dihydro-3-methyl-l,2,4-triazolo[4,3-c]pyrimidine-5-ones 51 (78MI1) (Scheme 22). 

The reaction of ethyl acetimidate with 3-aminopyridine-4-carboxylic acid yields 2-methylpyri-do[3,4-d]pyrimidin-4(3//)-one (12, R = Me).471 Whereas other isomeric aminopyridinecar-boxylic acids are not cyclized by this reagent, the application of ethyl benzimidate has proved to be successful in all cases studied. 

Aminopyridine-4-carboxylic acid (7 g, 0.05 mol), ethyl acetimidate (7 g, 0.08 mol), and MeOH (300 mL) were heated under reflux for 60 h. After distilling off 300 mL of the solvent, the solution was kept overnight at 0CC. The precipitated substance was recrystallized from a large amount of MeOH yield 3.5 g (4.3%) mp 309-310°C. 

Addition of 95% ethyl acetimidate (94 g, 1.02 mol) to 2-methylisourea hydrochloride (37.8 g, 341 mmol) caused a moderately exothermic reaction the temperature spontaneously rose to the bp in 10 min. The mixture was held at a gentle reflux by cooling and, after the reaction had subsided, was allowed to cool unaided for 1.5 h. Crystalline acetimidamide hydrochloride (25 g, mp 165-170 °C) was separated by filtration and the filtrate was fractionally distilled. After a forerun of 2,4,6-trimethyl l,3,5-triazine [yield 12.3 g (10%)]. the title compound was obtained (— 80°C/ 3 Torr) yield 34.6 g (73%) mp 43.5 C. The distillation residue (8 g) was nearly pure acetimidamide hydrochloride. 

Methyl-4-(4-pyridyl)-l,3,5-triazine (mp 99-102 °C)317 can be prepared in 16% yield by condensing ethyl isonicotinimidate with ethyl acetimidate and formimidamide. It is separated from the coproduct, 2-(4-pyridyl)-l,3,5-triazine, by diethyl ether extraction and repeated recrystallization. 

In the earliest example of this type of reaction,58 2-amino-5-methyl(N-p-tolyl)benzylamine and triethyl orthoformate were heated at 100°C for 1 hr to furnish a good yield of 6-methyl-3-p-tolyl-3,4-dihydroquinazoline (see l).58 The same authors obtained the 2-methyl homolog by substituting ethyl acetimidate (in boiling benzene) for the ortho ester. 

Nitriles and imidates have found little use, so far. Heating propionitrile and 2-aminobenzoic acid at 210°C in a closed vessel gave only a low yield of 2-methylquinazolin-4-one.297 Anthranilic add and 10 of its C-substituted derivatives were refluxed (5-50 hr) with ethyl acetimidate and benzimidate in methanol to give 2-methyl- and 2-phenylquinazolin-4-ones, respectively, in moderate yields three aminopyridine carboxylic acids behaved similarly.298 JV-Phenylbenzimidoyl chloride [PhC(NPh)Cl] and ammonium 2-aminobenzoate, in cold acetone, produced 2,3-diphenylquinazolin-4-one in good yield.299... 

A soln. of propargylamine in dioxane added dropwise to a refluxing soln. of ethyl acetimidate and a little p-toluenesulfonic acid in the same solvent, and refluxing continued 0.5 hr. 2,5(4)-dimethylimidazole. Y 87%. F. e. and methods s. E. Eloy, A. Deryckere, and J. P. Maffrand, Chim. Ther. 9, 602 (1974). 

Ethyl acetimidate hydrochloride and L-leucine in glacial acetic acid heated 2 hrs. at 80° with frequent shaking N,N -bis (L-a-carboxy-y-methylbutyl)-acetamidine. Y 76%. F. e., also with thioimidates, s. F. Weygand, W. Steglich, and D. Hoffter, B. 95, 2264 (1962). 

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