Kammari Laxminarayana, Plístil Lukás, Wirz Jakob, Klán Petr
Department of Organic Chemistry, Faculty of Science, Masaryk University, Kotlarska 2, CZ-611 37, Brno, Czech Republic.
Photochem Photobiol Sci. 2007 Jan;6(1):50-6. doi: 10.1039/b612233g. Epub 2006 Nov 6.
2,5-Dimethylphenacyl (DMP) carbamates (1a-c) released the corresponding free amines or amino acids in high chemical yields, albeit with quantum yields Phi of only 0.04-0.09, upon irradiation in either aprotic or protic solvents. The photoreaction proceeded principally from the triplet excited state via the E-photoenol. The lifetimes of the triplet enol and the E- and Z-enols in the ground state were determined by laser flash photolysis. The primary photoinitiated transformation liberated a carbamic acid derivative, which subsequently decarboxylated to the amino group-containing compound. Exhaustive irradiation of a DMP-protected aniline (1a) in acetonitrile did not provide aniline in quantitative chemical yields, because it was involved in reductive cleavage of the starting material as an electron donor, thereby decreasing the overall deprotection yield (86%). Phenylalanine methyl ester, liberated from 1c, was, however, obtained in excellent chemical yield (97%). It was also found that the carbamates, while thermally stable, released amines with higher quantum yields in acidic methanol solutions. The DMP chromophore is proposed as an excellent photoremovable protecting group for amino acids and, under specific conditions, for amines in organic synthesis and biochemistry.
2,5-二甲基苯甲酰基（DMP）氨基甲酸酯（1a - c）在非质子或质子溶剂中辐照时，能以较高的化学产率释放出相应的游离胺或氨基酸，尽管量子产率Φ仅为0.04 - 0.09。光反应主要通过E-光烯醇从三重激发态进行。通过激光闪光光解测定了三重态烯醇以及基态下E-烯醇和Z-烯醇的寿命。初级光引发转化产生一种氨基甲酸衍生物，随后该衍生物脱羧生成含氨基的化合物。在乙腈中对DMP保护的苯胺（1a）进行彻底辐照，无法以定量的化学产率得到苯胺，因为它作为电子供体参与了起始原料的还原裂解，从而降低了总体脱保护产率（86%）。然而，从1c释放出的苯丙氨酸甲酯以优异的化学产率（97%）得到。还发现，氨基甲酸酯虽然热稳定，但在酸性甲醇溶液中能以更高的量子产率释放胺。DMP发色团被认为是一种用于氨基酸以及在特定条件下用于有机合成和生物化学中胺的优异光可去除保护基团。
