Research On Bioreduction Of Saturated Aliphatic Aldehydes With α-chiral Carbon Centre

Biocatalysis has already become a profound tool in organic asymmetric synthesis, barker's yeast mediated reduction of carbonyl compounds, especially, has been a powerful tool for the synthesis of chiral alcohols. However, most researches nowadays focus on the reduction of carbonyl compounds and alkenes, while relatively less attention is paid to aldehydes, majority of which areα,β-unsaturated aldehydes. For baker's yeast mediated reduction of the saturated aldehydes withα-chiral center, few literatures can be referred to.In this thesis, research on bioreduction of saturated aliphatic aldehydes withα-chiral carbon centre was partially completed. Baker's yeast mediated reduction of 2-phenyl propanal is studied thoroughly, especially the effects of strains of baker's yeast, pH of the buffer, concentration of the substrate , the additives on the reduction and the solution system. It is found that (S)-2-phenylpronan-1-ol with relatively high e.e. value (64%) and a conversion of 65% can be reached when the reduction of 2-phenylpropanal is obtained in aqueous solution, pH8, with cultured baker's yeast as the catalyst, and a certain amount of ethyl 2-chloroacetate as addition.Furthermore, in this thesis, researches about the synthesis of someα-chloro aldehydes andα- bromo- aldehydes were carried out. Experiments ofα-chlorination/α- bromization of butyraldehyde, 3-methylbutanal, heptanal, 2-phenylacetaldehyde and 3-phenylpropanal were performed with L-proline, prolinamide and piperidine as catalysts, N-chloro- succinimide (NCS) or N-bromosuccinimide (NBS)as halogen sources. It was found that excellent yields and large scales ofα-chloro aldehydes andα- bromo- aldehydes can be attained when using L-proline as catalyst. Also, studies about the reduction of 2-chloro- butanal and 2-chloro-2-phenylacetaldehyde by baker's yeast were performed, but the efficiency of which were not so promising.In addition, the oxidation of alcohols to aldehydes with hetero- atoms like oxygen, nitrogen and sulfur was attempted here. With PCC, NaIO₄, and CrO₃, etc as oxidants, we investigated respectively the oxidation of 2-ethoxyethanol, 3-methoxypropane- 1,2-diol, 3-phenoxypropane -1,2-diol, 3-(benzyloxy)propane -1,2-diol and primary alcohols with nitrogen and sulfur.