The acetamidomethyl group has been found to be a useful protecting group for the thiol of cysteine. It was added to the thiol of cysteine and to the eight cysteines of the reduced S-protein of ribonuclease under acidic conditions. It is stable under the conditions commonly used in peptide synthesis and is removed by mercuric ion under mild conditions. The mercuric ion may be removed by treatment with H,S for small peptides and by gel filtration in the presence of mercaptoethanol for large peptides and proteins.

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Ethyl -Phthalimidoocetoacetate Ethylene Thioketal.-Ester II (5 g, 0.018 mol) and 2.7 g (0.028 mol) of ethanedithiol were dissolved in CHC13 and 5.8 ml of BF3-etherate was added. The solution was stirred 3 hr at 25°, then was washed with NaHCOg solution, dried, and concentrated. After long standing it partly crystallized from ¿-Pr20, 3.1 g, mp 71-72°. Anal. (CieHuXOJSa) C, , N, S.Pyrrolidine-2,4-dione 4-Ethylene Ketal (XIV).-NaOMe (0.32 g, 0.006 mol) wTas added to a solution of 2 g of XI (0.006 mol) and 0.23 g (0.007 mol) of NH2OH in MeOH. The solution turned pale yellow', then bright yellow, orange and, after 15 min, red. Shortly afterwards a solid precipitated. After 16 hr, the solid Xa salt of Ar-hydroxyphthalimide (0.6 g) was filtered, the filtrate was diluted with a large volume of i-Pr20 and more Na salt (0.25 g) was removed. The filtrate was concentrated giving 1.5 g of crude XIV, as an oil. This material slowly recrystallized and was then sublimed in vacuo and recrystallized from f-Pr20, to give 0.7 g of XIV, mp 98-101°. The compound shows a typical lactam absorption in the ir at 5.92 µ. Anal. (CeHgNOs) C, , N.

A series of methyl imidazo-[11,2-a]pyridine-2-carbamates was synthesized for anthelmintic testing. The preparation of this class of compounds was simplified by utilization of a novel one-step condensation of the appropriately substituted 2-aminopyridine and methyl chloroacetylcarbamate. The most potent compound, methyl 6-(phenylsulfinyl)-imidazo[1,2-a]pyridine-2-carbamate, was orally effective against a broad range of helminths in sheep and cattle, at a dosage of 2.5 mg/kg. Limited trials in swine and dogs demonstrated anthelmintic activity at higher dosages. Limited observations in sheep and cattle indicated that, in both species, a single oral dose of 200 mg/kg was well tolerated.