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首页> 外文期刊>Chemistry: A European journal >Chiral Catalysts Dually Functionalized with Amino Acid and Zn~2+Complex Components for Enantioselective Direct Aldol Reactions Inspired by Natural Aldolases: Design, Synthesis, Complexation Properties, Catalytic Activities,and Mechanistic Study
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Chiral Catalysts Dually Functionalized with Amino Acid and Zn~2+Complex Components for Enantioselective Direct Aldol Reactions Inspired by Natural Aldolases: Design, Synthesis, Complexation Properties, Catalytic Activities,and Mechanistic Study

机译：氨基酸和Zn〜2 +复合组分双重功能化的手性催化剂，用于天然醛缩酶的对映选择性直接醛醇反应：设计，合成，络合性质，催化活性和机理研究

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Aldolases are enzymes thatcatalyze stereospecific aldol reactionsin a reversible manner. Naturally oc-curring aldolases include class I aldo-lases, which catalyze aldol reactions viaenamine intermediates, and class II al-dolases, in which Zn~2+enolates of sub-strates react with acceptor aldehydes.In this work, Zn~2+complexes of L-prolyl-pendant[15]aneN_5(ZnL~3),L-prolyl-pendant[12]aneN_4(ZnL~4),andL-valyl-pendant[12]aneN_4(ZnL~5) weredesigned and synthesized for use aschiral catalysts for enantioselectivealdol reactions. The complexation con-stants for L~3to L~5with Zn~2+[logK_s-(ZnL)] were determined to be 14.1 (forZnL~3), 7.6 (for ZnL~4), and 9.6 forZnL~5), indicating that ZnL~3is morestable than ZnL~4and ZnL~5. The depro-tonation constants of Zn~2+-boundwater [pKa(ZnL) values] for ZnL~3,ZnL~4, and ZnL~5were calculated to be9.2 (for ZnL~3), 8.2 (for ZnL~4), and 8.6(for ZnL~5), suggesting that the Zn~2+ions in ZnL~3is a less acidic Lewis acidthan in ZnL~4and ZnL~5. These valuesalso indicated that the amino groupson the side chains weakly coordinate toZn~2+.We carried out aldol reactionsbetween acetone and 2-chlorobenzalde-hyde and other aldehydes in the pres-ence of catalytic amounts of the chiralZn~2+complexes in acetone/H_2Oat 25and 37 ℃. Whereas ZnL~3yielded the aldol product in 43 % yield and1 ee (R), ZnL~4and ZnL~5affordedgood chemical yields and high enantio-selectivities of up to 89% ee (R). UVtitrations of proline and ZnL~4with ace-tylacetone (acac) in DMSO/H_2O(1:2)indicate that ZnL~4facilitates the for-mation of the ZnL~4?(acac)-complex(K_app =2.1 x 10~2m~-1), whereas L-prolineforms a Schiff base with acac with avery small equilibrium constant. Theseresults suggest that the amino acidcomponents and the Zn~2+ions in ZnL4and ZnL5 function in a cooperativemanner to generate the Zn~2+-enolateof acetone, thus permitting efficientenantioselective C—C bond formationwith aldehydes.
机译：醛缩酶是以可逆方式催化立体特异性醛缩反应的酶。天然的醛缩酶包括I类醛缩酶和二类醛缩酶，II类醛缩酶通过烯胺中间体催化醛缩醛反应，其中Zn〜2 +底物的烯酸酯与受体醛反应。设计并合成了L-脯氨酸侧基[15] aneN_5（ZnL〜3），L-脯氨酸侧基[12] aneN_4（ZnL〜4）和L-戊基侧基[12] aneN_4（ZnL〜5）的配合物。使用对映体选择性手性催化剂的手性催化剂。确定L〜3至L〜5与Zn〜2 + [logK_s-（ZnL）]的络合常数为14.1（对于ZnL〜3），7.6（对于ZnL〜4）和ZnL〜5 9.6。 ZnL〜3比ZnL〜4和ZnL〜5更稳定。计算得出ZnL〜3，ZnL〜4和ZnL〜5的Zn〜2 +束缚水的去质子常数[pKa（ZnL）值]为9.2（对于ZnL〜3），8.2（对于ZnL〜4） ）和8.6（对于ZnL〜5），表明ZnL〜3中的Zn〜2 +离子比ZnL〜4和ZnL〜5中的酸性更低。这些值还表明侧链上的氨基与Zn〜2 +的配合力较弱。我们在丙酮/手性Zn〜2 +络合物的催化量下，进行了丙酮与2-氯苯甲醛-醛和其他醛的醛醇缩合反应。 H_2燕麦25和37℃。 ZnL〜3以43％的收率和1 ee（R）生成醛醇产物，而ZnL〜4和ZnL〜5的化学收率良好，对映选择性高达89％ee（R）。在DMSO / H_2O（1：2）中用乙酰丙酮（acac）对脯氨酸和ZnL〜4进行UV滴定表明ZnL〜4促进了ZnL〜4？（acac）络合物的形成（K_app = 2.1 x 10〜2m 〜-1），而L-脯氨酸形成带有一个acac的Schiff碱，且平衡常数很小。这些结果表明，ZnL4和ZnL5中的氨基酸成分和Zn〜2 +离子以协同方式起作用，生成丙酮的Zn〜2 +-烯醇酯，从而允许与醛形成有效的对映选择性C-C键。

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