Enzymatic and Organocatalyzed Asymmetric Aldolization Reactions for the Synthesis of Thiosugar Scaffolds

Abstract

We studied the synthesis of original thiosugar scaffolds by enantioselective aldolization. L‐Proline‐catalyzed C–C bond formation was the key step in the synthesis of L‐erythro‐thioketoses (3S,4R), whereas fructose‐6‐phosphate aldolase‐catalyzed reactions yielded the D‐threo‐thioketose series (3S,4S). By the organocatalytic approach, 5‐thio‐L‐ribulofuranose (1) and 5‐deoxy‐6‐thio‐L‐psicopyranose (2) were obtained in satisfactory overall yields from 2‐haloacetaldehydes, whereas 5‐thio‐D‐xylulofuranose (3) was synthesized in 50 % overall yield by an enzymatic aldolization reaction in only two steps from the same starting material.

Double Asymmetric Induction in Organocatalyzed Aldol Reactions: Total Synthesis of (+)‐2‐epi‐Hyacinthacine A2and (–)‐3‐epi‐Hyacinthacine A1

“…Interestingly, a peak corresponding to a carbonyl group (in the major diastereoisomer) could not be observed in 13 C NMR spectrum, whereas a peak at δ = 86.6 ppm was present; this indicated that the product assumed the cyclic, hemiaminal form, as confirmed by single‐crystal X‐ray diffraction analysis (Figure 1). 16 Reductive dehydroxylation of 2 proceeded without event and afforded desired pyrrolidine derivative 3 as a single isomer in 77 % yield. Upon exposure to ethanolic potassium carbonate, 3 was converted into tricyclic lactam 4 (92 %), and its stereochemical integrity was confirmed by X‐ray analysis (for the crystal structure of 4 , see the Supporting Information).…”

Synthesis of Specially Designed Probes to Broaden Transketolase Scope

“…Route B (Scheme ): To a suspension of SiO 2 ‐supported NaIO 4 37 (244 mg, 2 equiv.) in dichloromethane (4 mL) was added a solution of the diol 22 described below (125 mg, 0.5 mmol) in dichloromethane (4 mL), with stirring and at RT.…”

Recent Developments in the Preparation of Carbohydrate Derivatives from Achiral Building Blocks by using Aldolases

“…FSA has been demonstrated as a synthetically useful biocatalyst for the preparation of biologically relevant thiosugar scaffolds as well: condensation of DHA with 2‐haloacetaldehyde derivatives followed by halogen substitution with NaSH gave d ‐ threo ‐thiosugars in a straightforward manner (Scheme ) . Complementary l ‐ erythro ‐thiosugars not accessible under FSA catalysis can be obtained by l ‐proline organocatalyzed C−C bond formation between masked DHA and 2‐thio‐acetaldehyde derivatives.…”