Asymmetric carbon to nitrogen bond formation using optically-active allylic selenides: a new general method for the synthesis of N-protected optically-active .alpha.-amino acids
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
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.
Dihydroxyacetone Phosphate Aldolase Catalyzed Synthesis of Structurally Diverse Polyhydroxylated Pyrrolidine Derivatives and Evaluation of their Glycosidase Inhibitory Properties
The polyhydroxylated pyrrolidines generated were tested as inhibitors against seven glycosidases. Among them, good inhibitors of α‐L‐fucosidase (IC50=1–20 μM), moderate of α‐L‐rhamnosidase (IC50=7–150 μM), and weak of α‐D‐mannosidase (IC50=80–400 μM) were identified. The apparent inhibition constant values (Ki) were calculated for the most relevant inhibitors and computational docking studies were
Asymmetric carbon to nitrogen bond formation using optically-active allylic selenides: a new general method for the synthesis of N-protected optically-active .alpha.-amino acids
作者:Jeffrey N. Fitzner、Regan G. Shea、John E. Fankhauser、Paul B. Hopkins