The degradation of the antitumor agent gemcitabine hydrochloride in an acidic aqueous solution at pH 3.2 and identification of degradation products.

A study of the degradation kinetics of gemcitabine hydrochloride (2'-deoxy-2',2'-difluorocytidine) in aqueous solution at pH 3.2 was conducted. The degradation of gemcitabine followed pseudo first-order kinetics, and rate constants were determined at four different temperatures. These rates were used to construct an Arrhenius plot from which degradation rates at lower temperatures were extrapolated and activation energy calculated. Four major degradation products were identified. Only one of these degradation products, the uridine analogue of gemcitabine, was a known degradation product of gemcitabine and was identified by comparison with synthesized material. The other three degradation products were isolated and characterized by spectroscopic techniques. Two of these products were determined to be the diastereomeric 6-hydroxy-5, 6-dihydro-2'-deoxy-2',2'-difluorouridines, and the other product was determined to be O(6),5'-cyclo-5,6-dihydro-2'-deoxy-2', 2'-difluorouridine. The mechanisms of formation of these degradation products are discussed.

Metabolism and disposition of the antifolate LY231514 in mice and dogs.

The metabolism and disposition of LY231514 was studied in mice and dogs. LY231514 is a novel pyrrotopyrimidine-based multi-target antifolate (MTA) showing broad in vivo antitumor activity in mouse models and is currently in phase II human clinical trials. Doses (iv) of the compound showed high plasma levels, resulting in AUC values of 30-33 micrograms-hr/ml for mice and dogs after 20 and 7.5 mg/kg doses, respectively. The compound was eliminated rapidly. Half-life values for mice and dogs were about 7 and 2 hr, respectively. In vitro plasma binding measured 56% in mice, 46% in dogs, and 81% in humans. Fecal elimination was the major excretion pathway in mice after single iv doses of [14C]LY231514. Urine constituted the major route of excretion in dogs. Parent LY231514 accounted for the majority of urinary radiocarbon in mice (90%) and dogs (68%). Minor metabolites were found in urine, but the amounts were too small to isolate or identify. Based on an earlier observation that LY231514 photodegraded to produce reaction products having similar retention times as these minor urinary isolates, a photo-oxidation system was developed which in fact produced these metabolites. Subsequently, these photolytically-produced materials were used as standards to identify two novel in vivo metabolites formed by oxidation of the pyrrolo-pyrimidine ring system of LY231514. The oxidative transformations are similar to those observed for tryptophan and other indoles in that the pyrrole ring is oxidized to give an amide; further oxidation cleaves this ring, one ring carbon is lost, and a ketone is formed.

Isolation and structure elucidation of the major degradation products of cefaclor formed under aqueous acidic conditions.

The aqueous acidic degradation of the oral cephalosporin cefaclor was investigated. A number of degradation products were isolated and characterized. The degradation products can be loosely classified into three categories: thiazole derivatives, pyrazine derivatives, and simple hydrolysis or rearrangement products. Degradation pathways are proposed that involve (1) hydrolysis of the beta-lactam carbonyl with subsequent rearrangement, (2) ring contraction of the six-membered cephem nucleus to five-membered thiazole derivatives through an episulfonium ion intermediate, and (3) attack of the primary amine of the phenylglycyl side chain on the "masked aldehyde" at carbon-6 to form fluorescent substituted pyrazines.

Isolation and structure elucidation of the major degradation products of cefaclor in the solid state.

Cefaclor is a beta-lactam antibiotic that degrades slowly under normal storage conditions to several minor products. To obtain samples large enough to permit structure elucidation, cefaclor was allowed to degrade at 40 degrees C (75% relative humidity) and at 85 degrees C. The profile of degradation products formed under these conditions is qualitatively similar to the profile of degradation products observed in samples of cefaclor aged for 14 years at room temperature, although some products found in the sample degraded at 85 degrees C are not formed at the lower temperatures. Using preparative reversed-phase high-performance liquid chromatography (rp-HPLC) and a combination of spectroscopic methods, we have isolated and characterized 17 of these degradation products. Some of these products were also isolated from studies of aqueous degradations. The major products appear to have arisen from five distinct pathways: (1) isomerization of the double bond in the dihydrothiazine ring; (2) decarboxylation; (3) ring contraction of the cephem nucleus to thiazole structures; (4) oxidative attack at carbon 4 of the dihydrothiazine ring; and (5) intramolecular attack of the primary amine of the side chain on either the beta-lactam carbonyl to form 3-phenyl-2,5-diketopiperazines or the "masked aldehyde" at carbon 6 to form 2-hydroxy-3-phenylpyrazine derivatives. The pathway involving oxidation at carbon 4 is particularly important at ambient temperatures and is unique to the solid-state degradation.

Aqueous acidic degradation of the carbacephalosporin loracarbef.

The aqueous degradation of the carbacephalosporin loracarbef under moderately acidic conditions (pH range, 2.7-4.3) is described. Structures of a total of 10 compounds isolated by preparative reversed-phase HPLC have been proposed. Five of these 10 degradation compounds arose from hydrolysis of the beta-lactam ring followed by structural changes in the six-membered heterocyclic ring. Four compounds form from intermolecular reactions of loracarbef to form dimeric structures with peptide linkages. The remaining compound resulted from oxidation of the primary amine to a hydroxylamine. Pathways for the formation of these compounds from the parent loracarbef are proposed.

Isolation and structure elucidation of a novel product of the acidic degradation of cefaclor.

The acidic aqueous degradation of cefaclor, an orally administered cephalosporin antibiotic, has been investigated. The most prominent peak in the high-performance liquid chromatography profile of a degraded solution of cefaclor was isolated by preparative high-performance liquid chromatography. Mechanistically, the formation of this degradent from cefaclor involves a condensation of two cefaclor degradation products in which both products have undergone contraction from a six-membered cephem ring to a five-membered thiazole ring, presumably via a common episulfonium ion intermediate.

Disposition of zatosetron, a serotonin (5-HT3) receptor antagonist, in humans.

Zatosetron is being tested clinically as an antianxiety agent; it is a highly selective antagonist of the serotonin 5-HT3 receptor, with minimal agonist activity. The disposition of [14C]zatosetron was studied in five healthy men after a single oral dose (46.2 mg). Serum levels of radioactivity and parent drug peaked in 3-8 hr. About 15% more radioactivity was measured in red blood cells than in plasma. In serum, the parent compound represented about 85% of the radioactivity, zatosetron-N-oxide represented 10%, and N-desmethyl-zatosetron and 3-hydroxy-zatosetron each represented 2-3%. The t1/2 of zatosetron was 25-37 hr. About 75% of zatosetron added to human plasma became reversibly bound to protein. Concentrations of zatosetron in saliva were generally 10-50% higher than those in serum. About 80% of the administered radioactivity was eliminated in urine and 20% in feces; radioactivity was measurable in the excreta for 10-12 days after drug administration. The major route of metabolism of zatosetron was a stereoselective N-oxidation to form 8-alpha-methyl, 8-beta-oxo zatosetron (zatosetron N-oxide). In urine, approximately 45% of the radioactivity was unchanged zatosetron, 35% was zatosetron N-oxide, 10% was N-desmethyl-zatosetron, and 5% was 3-hydroxy-zatosetron. In feces, 30% of the radioactivity was unchanged zatosetron, and 70% was N-desmethyl-zatosetron. Overall, approximately 60% of the administered zatosetron was metabolized in humans. In a separate multiple-dose study, the disposition of zatosetron was found to be similar to that in the single-dose study.

The structure of A201A, a novel nucleoside antibiotic.

The structure of the novel nucleoside antibiotic A201A has been determined by a combination of chemical and spectroscopic methods. It is composed of 6-dimethylaminopurine, 3-amino-3-deoxyribose, p-hydroxy-alpha-methylcinnamic acid, a novel unsaturated hexofuranose and 3,4-di-O-methylrhamnose. Structures have also been assigned to several related minor factors simultaneously isolated from the fermentation broth. These unique nucleosides have very interesting similarities and differences in structure with the known antibiotics puromycin and hygromycin A.

A35512, a complex of new antibacterial antibiotics produced by Streptomyces candidus. II. Chemical studies on A35512B.

The glycopeptide antibiotic A35512B was isolated from Streptomyces candidus NRRL 8156 as the major active factor. Chemical degradation studies showed that mild hydrolysis resulted in the release, one molecule each, of four neutral sugars: rhamnose, fucose, glucose and mannose, as well as the liberation of a complex peptide core which retained all the amino acids and from which 3-amino-2,3,6-trideoxy-3-C-methyl-L-xylo-hexopyranose, a new amino sugar, was isolated (2). Oxidative degradation of A35512B resulted in the isolation of a chlorodiphenylether (5), dimethyl 4-methoxyisophthalate (7) and methyl 3,5-bis-(4-methoxycarbonylphenoxy(-4-methoxybenzoate (6). The structure of 5 could not be conclusively elucidated but was shown to be either 5-chloro-2',3-dimethoxy-2,5'-dicarbomethoxy diphenylether (5a) or 2-chloro-2',3-dimethoxy-5,5'-dicarbomethoxy diphenylether (5b) by physical methods. This halogenated fragment was shown to arise from oxidation of constituent amino acid (10) which has the aromatic substitution pattern of fragment (5a or 5b). Base hydrolysis resulted in the isolation of a phenanthridine (9) which arose from 2',4,6-trihydroxybiphenyl-2,5'-diyldiglycine. These chemical degradation studies on A35512B showed that this antibiotic is closely related to the ristocetin class of antibiotics.

Bicyclic and tricyclic ergoline partial structures. Rigid 3-(2-aminoethyl)pyrroles and 3- and 4-(2-aminoethyl)pyrazoles as dopamine agonists.

It is proposed, based upon comparisons with apomorphine, that the rigid pyrroleethylamine moiety of the ergolines is the portion of the molecule responsible for dopamine agonist activity. In support of this hypothesis, bicyclic and tricyclic ergoline partial structures 6, 11, 25, and 35 have been synthesized. In addition, some pyrazole isosters (37, 38, 40, and 45) of these rigid pyrroleethylamines have been made. All of the classes show dopaminergic activity in prolactin inhibition and in lesioned rat turning assays. The most potent drugs, the linear tricyclic pyrazoles 38 (R = Pr) and 40 (R = Pr), are comparable in potency with the highly active ergoline pergolide (41).

Microbial transformation of A23187, a divalent cation ionophore antibiotic.

A23187 is an ionophore antibiotic that forms dimeric complexes with divalent cations such an Mn2+ and Ca2+. Over 200 randomly selected soil microorganisms were incubated with A23187. None of these cultures was capable of transforming this compound. In contrast, many microorganisms were able to modify the methyl ester of A23187. The transformation products produced by one culture, Streptomyces chartreusis, were isolated and identified as 16-hydroxy-N-demethyl A23187 methyl ester, 16-hydroxy-A23187 methyl ester, and N-demethyl A23187 methyl ester. These ester derivatives lack most of the ionophore properties of the acids and cannot readily form dimeric complexes with divalent cations. However, they could be hydrolyzed by a mild treatment with ethanolic KOH to free acids that possess good ionophore activity. The use of the ester substrate in conjunction with the hydrolysis procedure is, at the present time, the only known method for microbiologically producing A23187 derivatives.

Synthesis and biological activity of 8-arylergolines.

9,10-Didehydro-6-methyl-8beta-arylergolines 2, in which the carboxyl group of lysergic acid and isolysergic acid is replaced by various aryl groups, were prepared in two steps by alkylation of aromatic substrates with the tetracyclic allylic alcohol 3, followed by aromatization with MnO2. The new ergolines 2 have modest prolactin-inhibiting and rat antimuricidal activities and possess significant alpha-blocking and antiserotonin properties.