1,721,012 research outputs found
METAL IONS AS POTENTIAL REGULATORY FACTORS IN THE BIOSYNTHESIS OF RED HAIR PIGMENTS: A NEW BENZOTHIAZOLE INTERMEDIATE IN THE IRON OR COPPER ASSISTED OXIDATION OF 5-S-CYSTEINYLDOPA
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ATROPOISOMERIC MELANIN INTERMEDIATES BY OXIDATION OF THE MELANOGENIC PRECURSOR 5,6-DIHYDROXYINDOLE-2-CARBOXYLIC ACID UNDER BIOMIMETIC CONDITIONS
No full textFORMATION OF NOVEL TETRAHYDROISOQUINOLINE RETINOIDS BY PICTET-SPENCLER REACTION OF DOPAMINE AND RETINALDEHYDE UNDER CONDITIONS OF RELEVANCE TO BIOLOGICAL ENVIRONMENTS
No full textNUOVI ASPETTI DELLA CHIMICA DI NEUROTRASMETTITORI MONOAMMINICI E DERIVATI CALECOLICI CORRELATI: REAZIONI CON ALDEIDI ED ALTRI SUBSTRATI DI INTERESSE BIOLOGICO
No full textLA SENSIBILITÀ CUTANEA, ESPRESSA IN TERMINI DI MED, COME FUNZIONE DEI LIVELLI DI MELANINA NELLA CUTE E NEI SUOI ANNESSI
No full textAn Unusual Decarboxylative Maillard Reaction between L-Dopa and glucose under biomimetic conditions: factors governing competition with Pictet-Spengler condensation
No full textIn 0.1 M phosphate buffer at pH 7.4 and 37 degreesC, the tyrosine metabolite L-3,4-dihydroxyphenylalanine (L-DOPA) reacts smoothly with D-glucose to afford, besides diastereoisomeric tetrahydroisoquinolines 1 and 2 by Pictet-Spengler condensation, a main product shown to be the unexpected decarboxylated Amadori compound N-(1-deoxy-D-fructos-1-yl)-dopamine (3). Under similar conditions, dopamine gave only tetrahydroisoquinoline products 4 and 5, whereas L-tyrosine gave exclusively the typical Amadori compound 6. Fe3+ and Cu2+ ions, which accumulate in relatively high levels in parkinsonian substantia nigra, both inhibited the formation of 3. Cu2+ ions also inhibited the formation of I and 2 to a similar degree, whereas Fe3+ ions increased the yields of I and 2. Apparently, the formation of 3 would not be compatible with a simple decarboxylation of the initial Schiff base adduct, but would rather involve the decarboxylative decomposition of a putative oxazolidine-5-one intermediate assisted by the catechol ring. These results report the first decarboxylative Maillard reaction between an amino acid and a carbohydrate under biomimetic conditions and highlight the critical role of transition metal ions in the competition with Pictet-Spengler condensation
A reinvestigation of the anaerobic conversion of adrenochrome to adrenaline black
No full textIn contrast to previous work, which suggested that adrenaline black, derived from adrenochrome under acid conditions, was a 3,4-linked polymer of 1-methyl-5,6-dihydroxyindole, two 2,3'-linked indole dimers (I, R = R1 = H; RR1 = bond) and a 4,7'-3',3''-linked trimer (II) have now been isolated. In the light of these results the transformation of adrenochrome to adrenaline black appears to be an uncorrected model for the study of melanogenesis
A Novel Octahydropyridobenzothiazepine Metabolite in Human Urine: Biomimetic Formation from the Melanogen 5-S-Cysteinyldopa and Formaldehyde via a Peculiar Sulfur-Controlled Double Pictet-Spengler Condensation.
No full textHPLC evidence is reported demonstrating the occurrence in some human urine samples of a novel catecholic metabolite, (3R,7S)-3,7-dicarboxy-10,11-dihydroxy-2,3,4,5,6,7,8,9-octahydropyrido[4,3-g][1,4]benzothiazepine (I). The compd. was shown to arise by a double Pictet-Spengler condensation of the urinary melanogen 5-S-cysteinyldopa with formaldehyde, in which regioselective formation of the six-membered ring ortho to the activating hydroxyl group lends assistance to the subsequent closure of the seven-membered 1,4-thiazepine moiety. Under physiol. relevant conditions, i.e., in 0.1 M phosphate buffer pH 7.4 and at 37°, the 7,8-dihydroxytetrahydroisoquinoline II (R = H) was the sole detectable intermediate in the formation of I. N-Acetylcysteinyldopa reacted likewise with formaldehyde to give the 7,8-dihydroxytetrahydroisoquinoline II (R = Ac). The anomalous regiochem. underlying formation of II (R = H, Ac) was rationalized with the aid of AM1/PM3 calcns. on a model alkylthiocatechol, predicting a higher HOMO-controlled reactivity on the position ortho rather than para to the activating hydroxyl group. The potential of the reported chem. as a convenient synthetic access to the 2,3,4,5-tetrahydro[1,4]benzothiazepine ring system is suggested by the efficient conversion of a cysteinylcatechol to III in the presence of formaldehyde
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