Highly efficient aldol additions of DHA and DHAP to N-Cbz-amino aldehydes catalyzed by l-rhamnulose-1-phosphate and l-fuculose-1-phosphate aldolases in aqueous borate buffer
作者:Xavier Garrabou、Jordi Calveras、Jesús Joglar、Teodor Parella、Jordi Bujons、Pere Clapés
DOI:10.1039/c1ob06263h
日期:——
Aldol addition reactions of dihydroxyacetone (DHA) to N-Cbz-amino aldehydes catalyzed by L-rhamnulose-1-phosphate aldolase (RhuA) in the presence of borate buffer are reported. High yields of aldol adduct (e.g. 70–90%) were achieved with excellent (>98 : 2 syn/anti) stereoselectivity for most S or R configured acceptors, which compares favorably to the reactions performed with DHAP. The stereochemical outcome was different and depended on the N-Cbz-amino aldehyde enantiomer: the S acceptors gave the syn (3R,4S) aldol adduct whereas the R ones gave the anti (3R,4R) diastereomer. Moreover, the tactical use of Cbz protecting group allows simple and efficient elimination of borate and excess of DHA by reverse phase column chromatography or even by simple extraction. This, in addition to the use of unphosphorylated donor nucleophile, makes a useful and expedient methodology for the synthesis of structurally diverse iminocyclitols. The performance of aldol additions of dihydroxyacetone phosphate (DHAP) to N-Cbz-amino aldehydes using RhuA and L-fuculose-1-phosphate aldolase (FucA) catalyst in borate buffer was also evaluated. For FucA catalysts, including FucA F131A, the initial velocity of the aldol addition reactions using DHAP were between 2 and 10 times faster and the yields between 1.5 and 4 times higher than those in triethanolamine buffer. In this case, the retroaldol velocities measured for some aldol adducts were lower than those without borate buffer indicating some trapping effect that could explain the improvement of yields.
报告了二羟基丙酮(DHA)与N-Cbz-氨基醛的 aldol 加成反应,该反应是在硼酸盐缓冲液存在下,由 L-鼠李糖-1-磷酸 aldol 酶(RhuA)催化进行的。大部分 S或 R 配置的受体都可以以高产率(例如 70–90%)获得 aldol 加合物,并具有优异的立体选择性(>98 : 2 syn/anti),这与使用 DHAP 进行的反应相比表现良好。立体化学结果不同,依赖于 N-Cbz-氨基醛的对映异构体:S 受体产生 syn(3R,4S)aldol 加合物,而 R 受体则产生 anti(3R,4R)联体异构体。此外,策略性地使用 Cbz 保护基团使得通过反相色谱或简单提取可以简单高效地去除硼酸盐和多余的 DHA。这一点,加上使用未磷酸化的供体亲核试剂,使得合成结构多样性免疫环醇的方法更为实用和高效。同时,评估了使用 RhuA 和 L-岩藻糖-1-磷酸 aldol 酶(FucA)催化剂在硼酸盐缓冲液中对 N-Cbz-氨基醛进行二羟基丙酮磷酸盐(DHAP)进行的 aldol 加成反应的表现。对于 FucA 催化剂(包括 FucA F131A),使用 DHAP 的 aldol 加成反应的初始速率是三乙醇胺缓冲液中反应的 2 到 10 倍,产率高出 1.5 到 4 倍。在这种情况下,测得某些 aldol 加合物的逆 aldol 速率低于不含硼酸盐缓冲液的情况,这表明存在某种捕获效应,可以解释产率的提高。