A New Insight in the Biosynthesis of Pheomelanins: Characterization of a Labile 1,4-Benzothiazine Intermediate
摘要:
It has long been known that pheomelanins, the distinctive pigments of red hair and celtic skin, arise by the oxidative cyclization of cysteinyldopas, mainly the 5-S-isomer 1, via 1,4-benzothiazines. However, the nature and reactivity of these intermediates have remained poorly defined. In an reexamination of the oxidation of 1, in aqueous buffers at physiological pHs, a hitherto unknown labile intermediate was identified and formulated as the 3-hydroxy-3,4-dihydro-1,4-benzothiazine 5 based on direct NMR analysis of the reaction mixture and conversion to the stable benzothiazines 3 and 4 under different conditions. Structure 5 was further supported by oxidation of the model compound 6 leading to the analogous more stable 2,2-dimethyldihydro-1,4-benzothiazine 9.
exhibited antitumoractivity against L1210 leukemia and B-16 melanoma in mice at doses which were not toxic to the host. Structural analogues of 5-S-cysteinyl-3,4-dihydroxyphenylalanine including several new compounds, were synthesized and tested for growth inhibition of cultured cells of human neuroblastoma YT-nu and Chinese hamster fibroblasts Don-6. Some were also examined for antitumoractivity against
A Novel Octahydropyridobenzothiazepine Metabolite in Human Urine: Biomimetic Formation from the Melanogen 5-<i>S</i>-Cysteinyldopa and Formaldehyde via a Peculiar Sulfur-Controlled Double Pictet−Spengler Condensation
作者:Paola Manini、Marco d'Ischi、Giuseppe Prota
DOI:10.1021/jo991969c
日期:2000.7.1
4-thiazepine moiety. Under physiologically relevant conditions, i.e., in 0.1 M phosphate buffer pH 7.4 and at 37 degrees C, the 7,8-tetrahydroisoquinoline 5 was the sole detectable intermediate in the formation of 2. N-Acetylcysteinyldopa (4) reacted likewise with formaldehyde to give the 7, 8-dihydroxytetrahydroisoquinoline 6. The anomalous regiochemistry underlying formation of 5 and 6 was rationalized
cyclization pathway. Pictet-Spengler cyclization of 2 and 3 proceeded with Felkin-Anh-type asymmetric induction, favouring the 1R isomer throughout the pH range 5.0-9.0. These results, which highlight the first example of carbohydrate-derived 7,8-dihydroxytetrahydroisoquinoline, provide new insights into the factors governing competition between Maillard and Pictet-Spenglercondensation pathways.
Twelve analogues of the antibacterial phenolic peptide 5-S-glutathionyl-beta-alanyl-L-dopa (5-S-GA-L-D: 1) were synthesized via orthoquinones using tyrosinase. Several synthesized compounds inhibited the v-Src autophosphorylation tyrosinekinase reaction with an IC50 value comparable to that of herbimycin. The inhibition of c-Src substrate phosphorylation was much less active than v-Src autophosphorylation
Spectroscopy and Photoreactivity of Trichochromes: Molecular Components of Pheomelanins†
作者:John D. Simon、Michael R. Goldsmith、Lian Hong、Valerie R. Kempf、Laura E. L. McGuckin、Tong Ye、Gerard Zuber
DOI:10.1562/2005-06-17-ra-578
日期:——
between the enol and keto forms of the molecule. These conclusions are supported by ground-state energies of these isomers obtained using a continuum solvation model. Near-infrared emission measurements were not able to detect photoproduction of 1O2, and spin-trapping experiments revealed formation of O2·−. DNA nicking assays also revealed a low level of light-induced aerobic activity of dTC, suggesting
摘要 毛色素是一类存在于褐黑色素(红色黑色素)中而在真黑色素(黑色黑色素)中不存在的小分子。在此检查了毛色素 F (TF) 和脱羧毛色素 C (dTC)。两种毛色素的特征在于可见吸收带,这表明这是顺式和反式异构体重叠转变的结果。dTC 吸收光谱的温度依赖性表明分子的烯醇和酮形式之间存在额外的平衡。这些结论得到使用连续溶剂化模型获得的这些异构体的基态能量的支持。近红外发射测量无法检测到 1O2 的光产生,自旋捕获实验揭示了 O2·-的形成。DNA 切口分析还显示 dTC 的光诱导有氧活性水平较低,表明光生成 O2·- 的量子效率最多为 5 × 10-6。这些结果与泵浦探针光学实验一致,揭示了在激发的几皮秒内有效且几乎完全的基态恢复。两种毛色素都是 1O2 的有效猝灭剂,表现出与维生素 C 相当的双分子速率常数。这些结果表明毛色素可以在褐黑素色素中发挥保护作用。