D‐Fructose‐6‐phosphate Aldolase in Organic Synthesis: Cascade Chemical‐Enzymatic Preparation of Sugar‐Related Polyhydroxylated Compounds

Abstract

Novel aldol addition reactions of dihydroxyacetone (DHA) and hydroxyacetone (HA) to a variety of aldehydes catalyzed by D-fructose-6-phosphate aldolase (FSA) are presented. In a chemical-enzymatic cascade reaction approach, 1-deoxynojirimycin and 1-deoxymannojirimycin were synthesized starting from (R)- and (S)-3-(N-Cbz-amino)-2-hydroxypropanal, respectively. Furthermore, 1,4-dideoxy-1,4-imino-D-arabinitol and 1,4,5-trideoxy-1,4-imino-D-arabinitol were prepared from N-Cbz-glycinal. 1-Deoxy-D-xylulose was also synthesized by using HA as the donor and either 2-benzyloxyethanal or 2-hydroxyethanal as acceptors. In both cases the enzymatic aldol addition reaction was fully stereoselective, but with 2-hydroxyethanal 17 % of the epimeric product at C2, 1-deoxy-D-erythro-2-pentulose, was observed due to enolization/epimerization during the isolation steps. It was also observed that D-(-)-threose is a good acceptor substrate for FSA, opening new synthetic possibilities for the preparation of important novel complex carbohydrate-related compounds from aldoses. To illustrate this, 1-deoxy-D-ido-hept-2-ulose was obtained stereoselectively by the addition of HA to D-(-)-threose, catalyzed by FSA. It was found that the reaction performance depended strongly on the donor substrate, HA being the one that gave the best conversions to the aldol adduct. The examples presented in this work show the valuable synthetic potential of FSA for the construction of chiral complex polyhydroxylated sugar-type structures.

Asymmetric Self‐ and Cross‐Aldol Reactions of Glycolaldehyde Catalyzed by D‐Fructose‐6‐phosphate Aldolase

“…Hence, the fact that GA is a better donor substrate than DHA may explain why when DHA and GA are mixed in the presence of FSA, 2 is the major product whereas the expected d-xylulose was not detected. [28] More importantly, a second in situ cross-aldol addition of HA to 2 was indeed possible, furnishing 1-deoxyd-ido-hept-2-ulose (5) [28] in 68 % yield (Scheme 3), whereas no reaction was detected with either DHA or GA. As judged by the ratio V max /K M , FSA functions with HA approximately 45 times better than with DHA, which might reflect the different reactivities of these substrates towards aldehyde acceptors. [28][29][30] Moreover, 2 binds to FSA at both the acceptor and donor sites, with an affinity similar to that of GA as the donor (Table 1, The kinetic data (Table 1) indicate that the apparent catalytic efficiency for GA is approximately 320-fold better as the donor than as the acceptor.…”

“…[27,28] This aldolase shows an unprecedented tolerance for donor substrates such as dihydroxyacetone (DHA), hydroxyacetone (HA), and 1-hydroxy-2-butanone. [28][29][30] In the course of our investigations on the catalytic properties of FSA, we discovered a new and unexpected activity of paramount importance: its ability to catalyze the direct stereoselective self-aldol addition of glycolaldehyde (GA) (1) to furnish d-(À)-threose (2) (Scheme 1). [31] In this reaction, GA (1) acts as both the donor and acceptor substrate for FSA.…”

“…The stereoselectivity observed was thus (2S,3R)-threo in agreement with previous work with other FSA-catalyzed aldol additions. [27][28][29][30] [32] Within the detection limits of high-field 1 H and 13 C NMR spectroscopy, only the syn diasteromer was observed.…”

Enzyme‐Catalyzed Aldol Additions

“…The use of DHA for the preparation of unphosphorylated targets simplifies the synthetic strategy avoiding the manipulation of the phosphate moiety and fostering the methodology to industrial applications. Most importantly, the FSA In terms of V m /K M , the FSA wild-type reactivity for the donors follows the order HA > GO >> DHA [106], and hence the DHA was the worse donor, which was also noticed when comparing the conversions of aldol additions of HA and DHA to the same aldehydes [104,105].…”

“…Interestingly, FSA Ala129Ser and TalB Phe178Tyr render mainly the cross-aldol reaction product of DHA and GO, whereas FSA wild type provides exclusively the self-aldolization product, d-threose [106]. FSA wild type also accomplishes cross-aldol additions of GO as acceptor with HA as donor [105].…”