Reactions of polyfunctional amino acids with N,N'-carbonyldiimidazole in aqueous solution--oligopeptide formation.

1. Serine reacts with N,N'-carbonyldiimidazole in aqueous solution at 0 degrees C to yield Nalpha-[imidazolyl-(1)-carbonyl]-L-serine. This compound slowly transforms to L-2-oxo-oxazolidine-5-carboxylic acid. We found that L-2-oxo-oxazolidine-5-carboxylic acid was stable to hydrolysis under a variety of conditions and did not oligomerize to yield peptides. Threonine was found to react in an analogous manner with N,N'-carbonyldiimidazole, yielding Nalpha-[imidazolyl-(1)-carbonyl]-L-threonine and L-(+)-trans-5-methyl-2-oxo-oxazolidine-5-carboxylic acid. 2. Histidine reacts with N,N'-carbonyldimidazole in aqueous solution at 0 degrees C to yield a variety of histidine-containing intermidiates. These slowly transform to give 7-carboxy-imidazole-[1,5cotetrahydropyrimidin-5-one in up to 90% yield. 3. The polymerization of 7-carboxy-imidazo-[1,5c]-tetrahydropyrimidin-5-one in imidazole buffer at 30 degrees gives excellent yields of oligohistidines.

6-aminopyrazolo[4,3-c]pyridin-4(5H)-one, a novel analogue of guanine.

Treatment of dimethyl alpha-ethoxymethylidineacetonedicarboxylate with hydrazine gave methyl 3-(methoxy-carbonylmethyl)pyrazole-4-carboxylate which, upon ammonolysis and dehydration, afforded methyl 3-(cyanomethyl)pyrazole-4-carboxylate. This compound, when heated with liquid ammonia, gave 6-aminopyrazolo[4,3-c]pyridin-4(5H)-one, a new guanine analogue, which did not possess any of the potent antiviral activity shown by 6-aminoimidazo[4,5-c]pyridin-4(5H)-one (3-deazaguanine).

N, N'-carbonyldiimidazole-induced diketopiperazine formation in aqueous solution in the presence of adenosine-5'-monophosphate.

3'(2')-O-glycyl-adenosine-5'-monophosphate is an intermediate in the conversion of N-[imidazoly-(1)-carbonyl]-glycine to diketopiperazine in the presence of adenosine-5'-monophosphate. The significance of these observations to prebiotic chemistry is discussed.

A comparison of chemiluminescent and radioenzymatic methods for the measurement of acetylcholine released from a rat phrenic nerve-hemidiaphragm preparation.

A chemiluminescent assay coupled to a periodide extraction method is described for the measurement of acetylcholine release from the vascular perfused rat phrenic nerve-hemidiaphragm preparation. A direct comparison of the chemiluminescent assay with an established radioenzymatic assay for acetylcholine demonstrates that the two assays are quantitatively equivalent and yield similar limits of sensitivity of approximately 2 pmol, and that the periodide extraction/chemiluminescent assay method is more consistent than the tetraphenylboron extraction/radioenzymatic assay method. Additionally, cholinergic drug interference with the chemiluminescent assay is minimal. The absence of radioactivity and the reduced cost of the chemiluminescent assay make it an attractive alternative to the radioenzymatic assay.