This article deals with design and synthesis of functional polymers having amino acid moieties in the main and side chains. The first half overviews peptides, polyamides, polyesters, polyurethanes, polysulfides, along with dendrimers consisting of amino acid repeating units in the polymer main chain synthesized by ring-opening polymerization, polycondensation, and polyaddition. The second half overviews polymers having amino acid and peptide moieties in the side chain mainly synthesized by radical polymerization of the corresponding vinyl monomers, some of which show unique properties concerning specific rotation, solubility, glass transition behavior, higher order structure, and drug-releasing function.
Biocatalyst has been attracted increasing attention for asymmetric synthesis due to the high enantioselectivities and environmentally friendliness. We have been developing methods using a fungus, Geotrichum candidum, which has many enzymes catalyzing the enantioselective oxidation and reduction reactions of non-natural substrates. These enzymes in the resting or dried cells were used in an organic solvent, supercritical carbon dioxide, or aqueous media for oxidation, reduction or deracemization reactions. The usefulness of these methods was also demonstrated in the preparation, on a multi-gram scale, of optically pure alcohols. The effect of fluorine substituents on the enantioselectivity of the reduction using the dried cell was also investigated thoroughly, and it was found that the reduction of trifluoromethyl ketones affords (S) -trifluoromethyl carbinols in excellent ee, whereas the reduction of methyl ketones gives the corresponding alcohols of the opposite configuration in excellent ee. The enzymes in the cells were separated to investigate the origin of different enantioselectivities between the methyl and trifluoromethyl ketones.
In order to gain insight into molecular basis for the sequence selective guanine alkylation by natural products aflatoxin B1 oxide and kapurimycin A3 we have synthesized epoxides with napthopyranone and anthrapyranone rings. Alkylation of guanine in DNA by these models proceeds with sequence selectivity similar to those of natural products. Absolute configuration of the epoxide side chain is significantly effective for the efficiency of guanine alkylation. Guanine alkylation most effectively proceeded at Gs in GG sequence, but G in the GC sequence was the least reactive site for the alkylation. The order of calculated energy levels of highest occupied molecular orbital (HOMO) for dinucleotide base pairs were in a good agreement with the G alkylation susceptibility experimentally obtained by our synthetic models. With these data we concluded that interaction of HOMO of DNA and LUMO of drugs is responsible for the sequence selectivity of guanine alkylation.
N-Substituted anilide derivatives bearing a large substitutent such as a tent-Bu group at the ortho-position have atropisomerism due to the high rotation barrier of the N-Ar bond and resist racemization. We have succeeded in the synthesis of such atropisomeric N-Ar amides, imides and lactams with high optically purity and definite absolute configuration, and the development of various asymmetric reactions using them. Furthermore, catalytic asymmetric reaction with such atropisomeric anilide as a chiral ligand is also described.
Photochemical cyclization of substituted o-alkylphenyl ketones and the thermal and acid-catalyzed reactions of the resulting benzocyclobutenols are described. The selective thermal ring opening of the benzocyclobutenol to the E-dienol was elucidated using the deuterated benzocyclobutenol and by thermal interconversion between two diastereomeric benzocyclobutenols. The 2, 2-dimethylbenzocyclobutenols having a hydroxy group on the β-carbon of the quaternary C1-alkyl group underwent stereospecific thermal isomerization by a 1, 5-sigmatropic hydrogen shift to give the 2-isopropenylphenyl alcohol through a twisted E-dienol. The benzocyclobutenols having a keto group on the β-carbon of the quaternary C1-alkyl group underwent thermal retro-aldol cleavage to give benzocyclobutenones. Acid-catalyzed reaction of benzocyclobutenols having α, α-dimethyl and β-hydroxy or β-acetoxy groups in their C1-alkyl chain gave isopropylidenebenzocyclobutene.
Highly coordinated organotin (IV) enolates were generated by the coordination of appropriate ligands to four-coordinated tin (IV) enolates. NMR studies revealed formation of five-coordinate O-stannyl enolates in the presence of hexamethylphosphoric triamide (HMPA) or tetrabutylammonium bromide (Bu4NBr). The highly coordinated enolates, which attained a marked change in chemoselectivity, have higher nucleophilicity to organic halides and lower reactivity to carbonyl compounds than four-coordinated reagents. The effective control of chemoselectivity in the intermolecularly competitive reaction between organic halides and carbonyl compounds was demonstrated using two types of tin enolates, a four-coordinated enolate and a highly coordinated one. An ab initio computational study uncovered the mechanism of the selective reaction of tin enolates in both cases with or without a ligand. It suggests that the coordination by a bromide anion causes an increase of nucleophilicity and a decrease of Lewis acidity of tin enolates. Michael addition of organotin (IV) ketone enolates to α, β-unsaturated esters took place with a catalytic amount of tetrabutylammonium bromide (Bu4NBr) to give δ-keto esters.