Enzymes, which catalyze a variety of reactions in living systems, have many specific features, such as regiospecificity, stereospecificity and substrate specificity. Furthermore, such reactions can be carried out under very mild conditions. Immobilization of biocatalysts (enzymes, and enzymecontaining organelles, microbial cells and other living systems) is attracting worldwide attention, because immobilized biocatalysts catalyze biochemical reactions under more stabilized conditions than their free counterparts and, moreover, they can be reused economically. At present, applications of immobilized biocatalysts include (a) production of useful compounds by stereospecific and/ or regiospecific reactions under mild conditions, (b) production of energy by biological processes, (c) analyses of various compounds with high sensitivity and high specificity, and (d) utilization in medical fields such as new types of drugs and artificial organs etc. This review deals with the several examples of immobilized biocatalysts applied to biosynthesis and bioconversion of organic compounds. Utilization of immobilized biocatalysts in the presence of organic solvents is also described.
This article describes diverse and versatile reactions of trichloroacetic acid and its anhydride involving decarboxylation of trichloroacetate ion. The reactions are characterized by the behaviors of trichloromethyl anion generated by the decarboxylation, i. e. trichloromethylation and abstraction of chlorine cation. Attention has been made, in the main, to a description of authors' works in the reactions with Schiff bases, enamines and conjugated olefins, and the reactions of α-trichloromethylated amines.
This article describes our recent synthetic studies on some kinds of alkaloids, which possess various carbon substituted piperidine parts in their structures, starting from a common synthon, N-substituted 1, 6-dihydro-3(2H)-pyridinone. Syntheses of catharanthine, ibogamine, epiibogamine, tabersonine, cleavamine, eburnamonine, corynantheidol, quinine, and tecomanine are involved.
Convergent and enantiospecific syntheses of compactin (1 a) and mevinolin (1 b), potent competitive inhibitor of HMG-CoA reductase, have been achieved via asymmetric intramolecular Diels-Alder reaction of acyclic (E, E, E) -trienone 4 leading to trans-octalone 3, a common intermediate for congeners. Chirality of C13 in 4 was designed to induce the four asymmetric centers with desired configuration by this reaction : the chirality controlled the approach of the dienophile from a single diastereotopic face. Trienone 4 was expeditiously constructed by the combination of two segments 5 and 6. Enantio- and stereo-specific synthesis of 6, a chiral 1, 3, 5- triol derivative, rested on the two novel methodologies, i.e, the convenient asymmetric reduction of β-keto carboxylate 19 d with baker's yeast and the regio- and stereo-selective iodofunctionalization (1, 3-asymmetric induction) of homoallylic carbamate. Preparation of 5 in its optically active form was accomplished by the elaboration of readily available γ-lactone 12.
A number of “Grignard-type” reactions of organic fluorine compounds were achieved by treating perfluoroalkyl iodides and substrates with zinc under the irradiation of ultrasound. The reactions include 1) Direct carboxylation of perfluoroalkyl iodides, 2) Perfluoroalkylation of carbonyl compounds, 3) Perfluoroalkylation of allyl, vinyl and aryl halides, and 4) Hydroperfluoroalkylation of alkynes and dienes.
Various organic compounds for conventional color photography by chromogenic development are reviewed. Compounds concerned with the dynamic processes of color development, i.e., color forming coupler, colored coupler, development inhibitor releasing (DIR) compounds and quinone-diimine scavenger, and with the static properties of color image such as hue and dye stability, are briefly described.
Asymmetric reduction of prochiral cyclic imines with chiral sodium acyloxyborohydrides (5 a-i), which are easily prepared by the reaction of NaBH4 with various N-acyl α-amino acids, has been investigated. Of these new reducing agents, triacyloxyborohydrides (5 c-f), derived from NaBH4 (1 eq.) and (S)-N-acylproline (3 eq.), were found to reduce 3, 4-dihydropapaverine (1) in tetrahydrofuran to (S)-norlaudanosine (2) in 60 % optical yield. The N-benzyloxycarbonyl derivative (5 c) could be isolated as a powder and characterized. The effect of solvents on this asymmetric reduction has been examined by the use of the isolated reagent (5 c) halogenated alkane solvents such as CH2Cl2 or CHCl2CH3 gave a better optical yield of compound (2) (70 % e. e.). The reagent (5 c); also reduced other cyclic imines (6 a-c) and (8) to the corresponding alkaloids (7 a-c) and (9) in excellent optical yields (70-86 % e. e.), providing an effective route to the asymmetric synthesis of these alkaloids. The asymmetric reduction of the imines (10 and 13) also proceeded smoothly to furnish the compounds (11 and 14), the precursors of TMQ and TA-073 (bronchodilating agents), in high optical yields. A possible reaction path for this reduction is also presented.