Intramolecular addition of the riboflavin side chain. Anion-catalyzed neutral photochemistry.
Intramolecular addition of the riboflavin side chain. Anion-catalyzed neutral photochemistry.
复制标题
核黄素侧链的分子内添加。
DOI：
--
复制
发表时间：
1975
期刊：
影响因子：
--
通讯作者：
P. Hemmerich
中科院分区：
文献类型：
--
作者：
M. Schuman Jorns;G. Schöllnhammer;P. Hemmerich
发现较高浓度（大于0.2 M）的二价阴离子A2-（磷酸氢盐、硫酸盐）的存在会加速并完全改变核黄素光解的过程：不是10-脱烷基化产生发光色素，而是分子内加成2 '-羟基被发现发生在邻近位置C（9）。该反应类似于Schöllnhammer和Hemmerich [Eur.（1974）44，561-577]。新的加成反应的最终产物由二氢黄素中间体的自氧化产生，并具有以下结构：因此，它是一类新的黄素（“环脱氢黄素”）的代表。关于“异常”黄素光降解产物在410 nm附近吸收的早期报道[Holmström（1964）方舟。凯姆22，281; Massey和Atherton（1962）J. Biol. Chem 237，2965]容易解释。发现该反应严格依赖于N（10）-侧链中亲核官能团的存在，例如N（10）-CH 2-C（OH）RR'或甚至N（10）-（CH 2）2-SO 3-。猝灭实验表明，新的反应发生通过单重态1FLox，而正常的光解是由三重态3Flox介导的。新的光加成反应是通过黄素-A2-复合物发生的，它为C（9）/O（2 'alpha）-相互作用创造了空间上有利的条件。
The presence of higher (greater than 0.2 M) concentrations of divalent anions A2- (hydrogenphosphate, sulfate) is found to accelerate as well as to change entirely the course of riboflavin photolysis: instead of 10-dealkylation to yield lumichrome, intramolecular addition of the 2'-hydroxyl group is found to occur at the peri-position C(9). The reaction is analogous to the "photohydration" of the flavin nucleus in the cationic state as described by Schöllnhammer and Hemmerich [Eur. J. Biochem. (1974) 44, 561-577]. The final product of the new addition reaction arises from autoxidation of a dihydroflavin intermediate and exhibits the structure. It is thus representative for a new class of flavins ("cyclo-dehydroflavins"). Earlier reports on "anomalous" flavin photodegradation products absorbing around 410 nm [Holmström (1964) Ark. Kem. 22, 281; Massey and Atherton (1962) J. Biol. Chem 237, 2965] are readily explained. The reaction is found to depend strictly on the presence of a nucleophilic function in the N(10)-side chain, e.g. N(10)-CH2-C(OH)RR' or even N(10)-(CH2)2-SO3-. Quenching experiments suggest that the new reaction occurs via the singlet state 1FLox while the normal photolysis is mediated by the triplet 3Flox. The new photoaddition is though to occur via a Flavin-A2- complex which creates sterically favorable conditions for C(9)/O(2'alpha)-interaction.