L-Rhamnulose-1-phosphate Aldolase from Thermotoga maritima in Organic Synthesis: One-Pot Multistep Reactions for the Preparation of Imino- and Nitrocyclitols

Rhamnulose-1-phosphate aldolase from Thermotoga maritima (Rhu1PATm) has been recently cloned and characterised. This hyperthermophilic enzyme offers intriguing possibilities for practical catalysis. This is due to its high stability under extreme reaction conditions, such as high temperature or the presence of organic co-solvents. The Rhu1PATm potentiality in organic synthesis has been explored focusing on (i) the reaction stereocontrol, (ii) the possibility of combining it with other mesophilic enzymes in multienzyme systems and (iii) its application to the synthesis of imino- and nitrocyclitols. In our study, the diastereoselectivity of Rhu1PATm was similar to the one reported for Rhu1PA from Escherichia coli (Rhu1PAEc). However, we observed significant differences for some aldehyde acceptors. Indeed, the diastereoselectivity control was not complete, since mixtures of L-threo (2R,3S; natural stereopreference) and D-erythro (2R,3R) diastereoisomers were obtained as described for Rhu1PAEc. Rhu1PATm was able to catalyse aldol reactions using nitroaldehydes and N-Cbz-aminoaldehydes. Conversion of the selected nitroaldehydes was complete, leading to mixtures of L-threo and D-erythro diastereoisomers, in 95:5 and 75:25 ratios. When N-Cbz-aminoaldehydes were used, aldol reaction yields were lower and the stereoselectivity L-threo:D-erythro ranged between 32:68 to>95:5.