Regioselective carbon-chain extension at 5'-position of nucleosides and 2-or 3-position of methyl 4, 6-Ο-benzylidene-D-hexopyranosides are described. Ο2-Methyluridine, N3-methyluridine, 4-triazoyl-1- (β-D-ribofuranosyl) -2 (1H) -pyrimidinone, and N1, N6, 2', 3'-Ο-tetrabenzoyladenosine reacted with 2, 6-di-t-butyl-4-nitrophenol, diethyl azodicarboxylate, and triphenylphosphine to give the corresponding 4- (nucleoside-5'-aci-nitro) -2, 6-di-t-butylcyclohexa-2, 5-dienones (aci-nitroester of nucleosides) without any detectable formation of products derived from the reaction at the 2'-and/or 3'-hydroxyl groups. The reaction of aci-nitroesters with stabilized Wittig reagents afforded carbon-chain extended nucleosides having 5'-6'-double bond. When the sequence of the reactions was carried out in one-pot procedure, the yields of 5-eno-furanosyl-pyrimidines and-purines were markedly increased. Methyl 2, 3-anhydro-4, 6-Ο-benzylidene-α-D-allopyranoside and-gulopyranoside reacted with allylic Grignard reagents giving the corresponding 2-deoxy-2-propenyl-α-D-hexopyranosides, while methyl 2, 3-anhydro-4, 6-Ο-benzylidene-α-D-mannopyranoside afforded 3-deoxy-3-propenyl-altropyranosides. The regioselectivity could be explained by diaxial opening of fixed epoxide ring. The reaction of 4, 6-Ο-benzylidene-1, 2-dideoxy-3-Ο-mesyl-D-ribo-hex-1-enopyranose and-xylo-hex-1-enopyranose with alkylmagnesium halides resulted in the formation of 1-C-and/or 3-C-substituted enopyranoses. On the other hand, allylic Grignard reagents selectively attack the 1-position of the 3-Ο-mesyl-glycals from β-side to afford 1-C-prop-2-enyl-β-D-hex-2-enitols.
Four synthetic routes to steroid CD-ring synthons possessing various side chains, and two methods for stereospecific introduction of steroid side chains at C (20) are presented. In the first approach, (-) - (R) - [3 (R) -hydroxy-5-methyl-1 (Z) -hexenyl] - (7aR) -methyl-4-hydroinden-5-one (4) and (+) - (1R) -acetyl- (7aR) -methyl-4-hydroinden-5-one (32) were synthesized by highly enantioselective double Michael addition of a chiral alkenyl copper-phosphine complex to 2-methyl-2-cyclopentenone in which C (23R) -allylic alcohol moiety served to control the cis stereochemistry at C (17) and C (13) as a key reaction. In the second approach, (±) -De-AB-cholestan-9-one (50) was synthesized by highly stereoselective double Claisen rearrangements of allylic alcohol 54, the first one to introduce the acyl chain at C (14) and the second to introduce the chain at C (13) with the right trans stereochemistry between 18-methyl and C (14) hydrogen, as well as the geometry of the [17 (20) E] -olefin. The C-ring was constructed by the cyclization of acyl carbanion and the side chain was introduced by the alkylation of the secondary tosylate 51 with acyl carbanion 70. (±) -De-AB-cholest-8 (14), 22-diene-9-one (74) and its optically active form were synthesized, in the third and fourth approaches, by double Claisen rearrangements of (±) -triol 78 and the palladium-catalyzed cyclization of (+) -1, 3-diene monoepoxide 122, respectively. In both approaches, the cis relative stereochemistry between 18-methyl and side chain at C (17) was introduced by the product development controlled methylation of 2-butenyl-3-alkylvalerolactone. In the syntheses of side chains, the 20 (R) -and 20 (S) -configurations were introduced by the alkylation of 20-tosyloxy steroids with the protected cyanohydrin 131 and by the palladium-catalyzed 1, 4-addition of nucleophiles to 15, 16-epoxy-E-17 (20) -alkylidene steroids.
We have shown that the enantioselective total synthesis of some useful antibiotics can be efficiently achieved by reasonable combination of enzymatic and non-enzymatic procedures. Our synthetic strategy for such optically active natural products is designed by the following principle. (1) Symmetrization : retrosynthesis is performed to generate, from the target molecule, a simplified symmetric diester in the prochiral or meso form as shown in Figure 1. (2) Asymmetrization : the symmetric diester is subjected to asymmetric hydrolysis with pig liver esterase (PLE) to generate the corresponding chiral half-ester (Enzymatic conversion of σ-symmetry substrate to C1-symmetry intermediate) (3) Non-enzymatic procedures : the chiral half-ester is converted to the target molecule and related molecules by means of usual organic synthesis, including some new method developed by us. Thus, various types of carbapenem antibiotics, negamycin, showdomycin, 6-azapseudouridine, cordycepin, aristeromycin, neplanocin A, and aminocyclitol-derivatives of fortimicin were efficiently synthesized with the desired absolute configurations.
With the use of cyclodextrins as catalysts, 4-hydroxybenzaldehydes, 4-hydroxybenzoic acids, 4-dichloromethyl-2, 5-cyclohexadienones, and indole-3-aldehyde are synthesized in virtually 100 % selectivities and in high yields. 4-Allyl-2, 5-cyclohexadienone is obtained also in 100 % selectivity using a modified cyclodextrin, in which all the primary hydroxyl groups are replaced by N-methyl-formamido groups. In addition, one-pot syntheses are successfully carried out with cyclodextrin as catalyst, yielding chalcones and β-nitrostyrenes in 100 % selectivity and in high yields. In the absence of cyclodextrins, however, both the yields and the selectivities for the desired products in all the reactions are quite low. The selective catalyses by cyclodextrins involve, a) regulation of mutual orientation of reactants, b) regulation of molecular size of intermediates and products, c) protection of unstable intermediates and products, and/or d) solubilization of reactants with poor solubilities. The mechanisms of selective catalyses are clarified using the conformations of the molecular complexes, formed from cyclodextrins and reactants in the reaction mixtures, which are determined by 1H-and 13C-NMR spectroscopy. Furthermore, 4-hydroxybenzoic acid and 4-hydroxybenzaldehyde are synthesized in almost 100 % selectivity using cyclodextrins, immobilized with epichlorohydrin as crosslinking agent, as catalysts. The immobilized catalysts are easily separated from the reaction mixtures, and are successfully used many times without measurable decrease in catalytic activities.
Selective synthesis of high octane value gasoline from light olefins was investigated by developing novel shape-selective metallosilicates. The metallosilicates were synthesized by replacing the Al ingredient of ZSM-5 zeolite with various metal at the stage of gel formation in the rapid crystallization method. Among various metallosilicates, iron-group metal silicates were found to exhibit the highest selectivity to light olefins from methanol. Therefore, preparation method of the Fe-silicate was studied more extensively. It was proved that the Fe ingredient is concentrated in the core part of the crystal particles, especially in Fe-silicates having high Si/Fe atomic ratios, and the particles are covered by Fe-poor silica layer. Light olefins were exclusively converted to gasoline on these Fe-silicates ; e. g. 95.6 % propylene fed was converted to a high octane value (95) gasoline with a very high space-time yield (8.09kg/l·h) at 295°C and a space velocity of 4, 500h-1. The catalytic activity of the Fe-silicate for propylene conversion and the selectivity to gasoline was consistently maintained at least 100h on stream under the corresponding condition of SV 1, 000h-1.
Tin (II) =trifluoromethanesulfonate (triflate), easily prepared from tin (II) chloride and trifluoromethanesulfonic acid, is employed for the generation of tin (II) enolates from the corresponding ketones and 3-acylthiazolidine-2-thiones. The tin (II) enolates thus formed react smoothly with aldehydes or ketones to afford the corresponding aldol products in highly stereoselective manner. According to this procedure, various kinds of synthetically useful polyoxygenated compounds are obtained stereoselectfirely. The most characteristic property of tin (II) enolates is that high asymmetric induction is realized only by the addition of chiral diamines derived from (L) -proline as ligands to the center tin (II) metal. Thus, highly optically active aldols are obtained starting from two different achiral carbonyl compounds. It should be noted that, in some cases, relative stereochemistry of aldols can be controlled by the addition of a diamine as a ligand to the intermediate tin (II) enolates.