L-Rhamnulose-1-phosphate and l-fuculose-1-phosphate aldolase mediated multi-enzyme cascade systems for nitrocyclitol synthesis

Abstract

One-pot multistep stereoselective cascade reactions were implemented for the straightforward synthesis of various nitrocyclitols. Two kinases, an aldolase and a phosphatase were involved in this process, together with a spontaneous intramolecular Henry reaction to provide the nitrocyclitol moiety. The CC bond formation catalysed by the aldolase and the nitroaldol reactions were key steps to build the carbocycle stereoselectively. The aldolase acceptor substrates were all 4-nitrobutanal structurally based, either hydroxylated or unsubstituted at the C2 and/or C3 positions. l-Fuculose-1-phosphate aldolase (FucA) catalysed the formation of the expected (R,R)- or d-erythro aldol, except in the case of 4-nitrobutanal, from which the epimeric (R,S)- or l-threo aldol was also formed. l-Rhamnulose-1-phosphate aldolase consistently formed the expected (R,S)- or l-threo aldol together with a minor amount of (R,R)- or d-erythro aldol. The intramolecular Henry reaction was also found to be stereoselective, occurring spontaneously once the aldol was formed due to the presence of both ketone and a terminally positioned nitro group. The combination of this set of reactions successfully furnished 11 nitrocyclitols which have not been described previously in the literature.