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Antamanide is the name we have given to a constituent of the fungus Amanita phalloides. This substance counteracts the lethal action of the Amanita toxins phalloidine and u-amanatine if administered to the white mouse before, or simultaneously with, the poisons. Its concentration in the fungus is, however, so low that the toxic action of the latter predominates. Antamanide is a cyclic decapeptide formed from the L-amino acids alanine, phenylalanine, proline, and valine in the molar ratio 1:4:4:f. The amino-acid sequence was determined by a combination of gas chromatography and mass spectrometry. The structural formula assigned was confirmed by synthesis according to a classic route of peptide chemistry.

1. The uricosuric drug benzbromarone is extensively metabolized in man and two main metabolites are formed: the previously characterized 1'-hydroxybenzbromarone (metabolite M1) and an arylhydroxybenzbromarone (metabolite M2) of unknown structure. A dimethyl derivative was isolated from urine after methylation and was characterized by gas chromatography-mass spectrometry (g.l.c.-m.s.) and high resolution nuclear magnetic resonance spectroscopy as 4''-O-methyl-6-methoxybenzbromarone; the structure of M2 therefore is 6-hydroxybenzbromarone. 2. A minor metabolite was similarly characterized as 1'-oxobenzbromarone by comparison with authentic synthetic samples and is a product of biodegradation and not an artifact derived from the in vitro oxidation of 1'-hydroxybenzbromarone. Further minor metabolites were detected and were provisionally characterized by g.l.c.-m.s. after derivatization and include: 2'-hydroxybenzbromarone (an isomer of 1'-hydroxybenzbromarone); 1',6-dihydroxybenzbromarone; dihydroxy-aryl-benzbromarone; and two structure isomers of 6-hydroxybenzbromarone. Debrominated metabolites were not detectable. 3. Benzbromarone is hydroxylated in vivo at the prochiral centre C1' to 1'-hydroxybenzbromarone; analysis of 1'-hydroxybenzbromarone from plasma and urine extracts by h.p.l.c. using a chiral column revealed that two peaks were eluted which showed a mean enantiomeric ratio of 2.1 for plasma and 7.3 for urine; these data demonstrate that the formation and elimination of this metabolite is enantioselective; the absolute configuration of the 1'-chiral centre is presently unknown.

Following oral administration of the uricosuric drug benzbromarone two major metabolites appear in the circulation. 1'-hydroxy-benzbromarone (M1), and a second product (M2) of unknown structure. The plasma concentrations of the parent drug and of M1 and M2 have now been compared in two different elimination phenotypes. 10 subjects who eliminated the drug rapidly (S1-10) and one individual (S11) whose elimination capacity was impaired, presumably due to genetic variation (S11). The AUC (0-96) of the parent drug in S11 was 145 micrograms.ml-1 h. and in the other individuals it averaged 18.3 (11.4-24.5) micrograms.ml-1 h. The plasma elimination half life of benzbromarone was 3.34 (1.77-5.24) h in the rapid eliminators, and 13.08 h in the subject with the elimination defect. The mean plasma elimination half life of the metabolites in S1-10 amounted to 20.1 (11.9-41.2) h for M1, and 17.2 (12.9-30.7) h for M2. In S11 the plasma elimination half life of M1 was prolonged to 76.6 h, and of M2 to 75.4 h. Thus, the elimination defect in S11 was not restricted to the parent drug, but it also involved the two major metabolites M1 and M2. This might be a consequence of a hepatic enzyme deficiency, or be due to impairment of drug excretion.