Aldol Additions of Dihydroxyacetone Phosphate to N‐Cbz‐Amino Aldehydes Catalyzed by L‐Fuculose‐1‐Phosphate Aldolase in Emulsion Systems: Inversion of Stereoselectivity as a Function of the Acceptor Aldehyde

Abstract

The potential of L-fuculose-1-phosphate aldolase (FucA) as a catalyst for the asymmetric aldol addition of dihydroxyacetone phosphate (DHAP) to N-protected amino aldehydes has been investigated. First, the reaction was studied in both emulsion systems and conventional dimethylformamide (DMF)/H2O (1:4 v/v) mixtures. At 100 mM DHAP, compared with the reactions in the DMF/H2O (1:4) mixture, the use of emulsion systems led to two- to three-fold improvements in the conversions of the FucA-catalyzed reactions. The N-protected aminopolyols thus obtained were converted to iminocyclitols by reductive amination with Pd/C. This reaction was highly diastereoselective with the exception of the reaction of the aldol adduct formed from (S)-N-Cbz-alaninal, which gave a 55:45 mixture of both epimers. From the stereochemical analysis of the resulting iminocyclitols, it was concluded that the stereoselectivity of the FucA-catalyzed reaction depended upon the structure of the N-Cbz-amino aldehyde acceptor. Whereas the enzymatic aldol reaction with both enantiomers of N-Cbz-alaninal exclusively gave the expected 3R,4R configuration, the stereochemistry at the C-4 position of the major aldol adducts produced in the reactions with N-Cbz-glycinal and N-Cbz-3-aminopropanal was inverted to the 3R,4S configuration. The study of the FucA-catalyzed addition of DHAP to phenylacetaldehyde and benzyloxyacetaldehyde revealed that the 4R product was kinetically favored, but rapidly disappeared in favor of the 4S diastereoisomer. Computational models were generated for the situations before and after C-C bond formation in the active site of FucA. Moreover, the lowest-energy conformations of each pair of the resulting epimeric adducts were determined. The data show that the products with a 3R,4S configuration were thermodynamically more stable and, therefore, the major products formed, in agreement with the experimental results.

Dihydroxyacetone Phosphate Aldolase Catalyzed Synthesis of Structurally Diverse Polyhydroxylated Pyrrolidine Derivatives and Evaluation of their Glycosidase Inhibitory Properties

“…The configuration at positions C-3 and C-4 was controlled by the DHAP aldolase. The stereogenic center at C-2 was generated during the reductive amination and depends, in most cases, on the stereochemistry at C-4, [24,25] whereas the stereochemistry at C-5 is fixed by the starting aldehyde.…”

“…[24,25] The key step of the strategy devised was the aldol addition of dihydroxyacetone phosphate (DHAP) to N-benzyloxycarbonylaminoaldehydes catalyzed by DHAP aldolases, such as d-fructose-1,6-diphosphate aldolase from rabbit muscle (RAMA), and l-rhamnulose-1-phosphate aldolase (RhuA) and l-fuculose-1-phosphate aldolase (FucA), both from E. coli. This methodology allowed us to prepare a number of iminocyclitols from N-Cbz-3-aminopropanal, N-Cbz-glycinal, and both enantiomers of NCbz-alaninal.…”

Influence of secondary reactions on the synthetic efficiency of DHAP‐aldolases

“…Soluble recombinant His-tagged FucA overexpressed in E.coli, and produced in our laboratory according to reported procedures (Durany et al, 2004), has been used as a biocatalyst. DHAP was the limiting reagent, with an aldehyde excess of 1.75 (Espelt et al, 2005) (see Materials and Methods for details).…”

“…Previous results using recombinant His-tagged FucA produced in our laboratory (Durany et al, 2004;Vidal et al, 2003), led to the synthesis product, (3R,4R,5S)-5-(benzyloxycarbonylamino)-5,6-dideoxy-1-O-phosphonohex-2-ulose, with a 100% diastereomeric excess (Espelt et al, 2005). (Fessner et al, 1993).…”

Structure of a Class I Tagatose-1,6-bisphosphate Aldolase

“…In 2-keto-4-hydroxyglutarate aldolase (19) and in L-fuculose-1-phosphate aldolase, racemization occurs at C4 of the condensation products, resulting from random orientation of the aldehyde during stereofacial attack (20) and from its chemical nature (21). In contrast, configuration at both C3 and C4 is not retained in the catalytic mechanism of the class I TBP aldolase from S. aureus, given that aldol condensation yields a mixture of sorbose bisphosphate, psicose bisphosphate, fructose bisphosphate, and tagatose bisphosphate (5).…”