Mass spectrometric identification of amino acid transformations during oxidation of peptides and proteins: modifications of methionine and tyrosine.

Liquid chromatography/electrospray ionization mass spectrometry (LC/ESI-MS), tandem mass spectrometry with on-line liquid chromatography (LC/ESI-MS/MS) and high-resolution mass spectrometry with liquid secondary ionization (LSI-MS) were utilized to identify the modified amino acids in peptides and proteins formed during oxidation with performic acid. The procedure of protein oxidation was chosen to assist in protein unfolding by oxidizing the cystines to cysteic acids to allow for more complete proteolytic digestion and to create additional cleavage sites for endoproteinase Asp-N. Investigation of the Asp-N peptide map of oxidized superoxide dismutase (SOD) by LC/ESI-MS revealed that an expected proteolytic fragment of the protein was missing. In its place, two peptides with molecular weights 66 and 100 higher than that calculated for the missing peptide were observed. To identify the modified amino acids in the unexpected peptides, a model peptide with some amino acid similarities (tyrosine, arginine, methionine, lysine) to the missing peptide was chosen and was subjected to similar oxidation and enzymatic digestion steps, conditions, and reactions. After oxidation and digestion, the model peptide (TAP; sequence, Ac-MDKVLNRY) showed three major peaks in LC/MS. The peptides in the three peaks were identified as the unmodified peptide and two peptides whose molecular weights were 66 and 100 higher than that of TAP.(ABSTRACT TRUNCATED AT 250 WORDS)

3,4-Diphenyl-1H-pyrazole-1-propanamine antidepressants.

A small series of compounds is described in which a narrow SAR has identified N,N-dimethyl-3,4-diphenyl-1H-pyrazole-1-propanamine, 3, as a potential antidepressant with reduced side effects. The isomeric N,N-dimethyl-4,5-diphenyl-1H-pyrazole-1-propanamine was completely inactive in the primary antidepressant screens. Compounds were synthesized by Michael addition of acrylonitrile to diphenylpyrazole followed by reductive alkylation of the resultant diphenylpyrazolepropionitriles. Compound 3 was equipotent with imipramine in standard antidepressant assays in animals but showed no significant anticholinergic action and did not antagonize the antihypertensive effects of clonidine and guanethidine.

Experimental antiulcer drugs.4. 1,3-Disubstituted 2,4,5,6-tetrahydro-4,6,6 -trimethyl-2-phenylcyclopenta[c]pyrrole-4-carboxamides.

The synthesis of 1,3-disubstituted 2,4,5,6-tetrahydro-4,6,6-trimethyl-2-phenylcyclopenta[c]pyrrole-4-carboxamides is reported. The derivatives included R1 = R3 = H, R1 = CH2OH with R3 = H (16) or CH3, R1 = CH3 with R3 = CH2OH (17), and R1 = R3 = CH2OH. The monohydroxymethyl derivatives were as active as the parent cyclopentapyrrole, where R1 = R3 = CH3 (1), when administered orally in the pyloric ligated rat. The compounds lacking one or both CH3 groups at C-1 or C-3 were much less active. Compounds 16 and 17 inhibited histamine-induced gastric acid secretion in the dog.

Experimental antiulcer drugs. 2. 2-Substituted 2,4,5,6-tetrahydro-1,3,4,6,6-pentamethylcyclopenta[c]pyrrole-4-carboxamides.

Condensation of a 1-substituted 2,5-dimethylpyrrole 6 with 2 mol of 2-amino-2-methylpropionitrile in hot acetic acid yielded a 2-substituted 2,4,5,6-tetrahydro-1,3,4,5,6,6-pentamethylcyclopenta[c]pyrrole-4-carbonitrile (4). Hydrolysis of the nitriles to the amides gave a group of compounds which were active as antisecretory agents in the pyloric-ligated rat. Outstanding in this respect was the 2-phenyl derivative 5b, the most active compound in the series. It did not possess anticholinergic properties. In contrast to the indoles and pyrroles reported earlier, 5b demonstrated marked activity in blocking gastric acid secretion in the histamine-stimulated dog.