Kazunobu Toshima

Glycosyl fluorides in glycosidations.

This short review deals with the recent progress in chemical O-glycosidation and C-glycosylation methods using glycosyl fluorides as glycosyl donors. Pyranosyl and furanosyl fluorides were effectively activated by fluorophilic reagents such as SnCl2-AgClO4, SnCl2-TrClO4, SnCl2-AgOTf, TMSOTf, SiF4, BF3 x Et2O, TiF4, SnF4, Cp2MCl2-AgClO4 (M = Zr or Hf), Cp2ZrCl2-AgBF4, Cp2HfCl2-AgOTf, Bu2Sn(ClO4)2, Me2GaCl, Tf2O, LiClO4, Yb(OTf)3, La(ClO4)3 x nH2O, La(ClO4)3 x nH2O-Sn(OTf)2, Yb-Amberlyst 15, SO4/ZrO2, Nafion-H, montmorillonite K-10, and TrB(C6F5)4 to react with alcohols to give the corresponding O-glycosides in high yields. Furthermore, several types of C-glycosyl compounds, such as aryl, allyl and alkyl C-glycosyl derivatives, were also obtained by the glycosylation using glycosyl fluorides and the corresponding nucleophile with or without a Lewis acid.

Novel lipase-catalyzed ring-opening copolymerization of lactide and trimethylene carbonate forming poly(ester carbonate)s.

Poly(lactide-co-trimethylene carbonate)s were prepared by the lipase-catalyzed ring-opening copolymerization of lactide and trimethylene carbonate having carbonate content from 0 to 100%. Their thermal properties and enzymatic degradability were measured. The L,L-, D,D- and D,L-lactides were copolymerized with trimethylene carbonate by porcine pancreatic lipase to produce random copolymers having molecular weights of up to 21000. The glass transition temperature (Tg of the copolymer was dependent on the carbonate content and the Tg values linearly decreased from 35 degrees C (polylactide) to -8 degrees C [poly(trimethylene carbonate)]. Among the lipases tested, the porcine pancreatic lipase and proteinase K showed biodegradability towards poly(ester-carbonate)s.

Enantiospecific Total Synthesis of a β-Glucosidase Inhibitor, Cyclophellitol

Abstract Cyclophellitol has been synthesized from L-glucose through an intramolecular cycloaddition of a nitrile oxide derived from an oxime.

Perspectives for synthesis and production of polyurethanes and related polymers by enzymes directed toward green and sustainable chemistry

Enzyme-catalyzed polymerization and degradation will play an important role in both the synthesis and chemical recycling of green and sustainable polyurethane. This minireview covers the new synthetic routes to polyurethane without using diisocyanate, the biodegradation of polyurethane, and the enzymatic synthesis and the chemical recycling of poly(ester-urethane) (PEU) and poly(carbonate-urethane) (PCU). The lipase-catalyzed polymerization of low molecular weight and biodegradable urethanediols with short-chain dialkyl carbonate and alkanedioates produced PCU and PEU, respectively. They were readily degraded in an organic solvent into the repolymerizable cyclic oligomers by lipase as a novel chemical recycling. These results will be applicable for the production strategies of green and sustainable polyurethanes.

Target-selective photo-degradation of HIV-1 protease by a fullerene-sugar hybrid

A designed fullerene-sugar hybrid effectively and selectively degraded the target protein, HIV-1 protease, which has high affinity for the fullerene moiety; degradation was achieved using long-wavelength UV or visible photo-irradiation, in the absence of any additives and under neutral conditions.

High-Molecular-Weight Polycarbonates Synthesized by Enzymatic ROP of a Cyclic Carbonate as a Green Process

High-molecular-weight PTeMC and PHMC were prepared by the lipase-catalyzed polymerization of butane-1,4-diol or hexane-1,6-diol and diphenyl carbonate via the formation of a cyclic dimer by a green process. Cyclic carbonate dimers were prepared by the lipase-catalyzed condensation of diphenyl carbonate with butane-1,4-diol or hexane-1,6-diol in dilute toluene solution using an immobilized lipase from Candida antarctica, and was followed by the ring-opening polymerization of the cyclic dimer in bulk with the same lipase to produce PTeMC with M(w) = 119 000 g . mol(-1) and PHMC with M(w) = 399 000 g . mol(-1), respectively. Additionally, enzymatic polymerization of cyclic carbonate dimer was analyzed with respect to the K(m) and V(max) for the lipase.

Direct Enzymatic Synthesis of a Polyester with Free Pendant Mercapto Groups

An aliphatic polyester with free pendant mercapto groups was prepared by direct lipase-catalyzed polycondensation of hexane-1,6-diol and dimethyl 2-mercaptosuccinate. The polycondensation reaction using immobilized lipase from Candida antarctica (lipase CA) was carried out in bulk at 70 degrees C without any formation of disulfide or thioester linkages to produce the corresponding polyester with Mw = 14000 g/mol in high yield. The content of free mercapto groups in the polyester could be controlled by copolymerization with other monomers. The obtained polyester was easily cross-linked to form gels by the air oxidation of the pendant thiols to disulfides in dimethyl sulfoxide.

A novel greener glycosidation using an acid–ionic liquid containing a protic acid

Abstract The glycosidations of glucopyranosyl diethyl phosphite and alcohols using an ionic liquid, 1- n -hexyl-3-methylimidazolium trifluoromethanesulfonimidide (C 6 mim[NTf 2 ]) containing a protic acid, trifluoromethanesulfonimide (HNTf 2 ), as a novel solvent-catalyst system, effectively proceeded under mild conditions to give the corresponding glycosides in good to high yields. Furthermore, this acid–ionic liquid combination could be reused many times for the glycosidations without any loss in efficiency.

Total synthesis of elaiophylin (azalomycin B)

Antibiotic elaiophylin 1a has been first synthesized by a convergent route involving aldol condensation between (5R,6R,7R)-5-0-[2′-deoxy-3′,4′-di-0-(dimethylisopropylsilyl)-α-L-fucopyranosyl]-6-ethyl-7-0-(diethylisopropylsilyl)-5,7-dihydroxy-3-octanone 3a and (7S,8S,15S, 16S) - (3E, 5E, 11E, 13E) -8,16-bis [ (1 ′R) -1′ -formylethyl] -7,15-dimethyl-1, 9-dioxacyclohexadeca-3,5, 11,13-tetraene-2,10-dione 4, followed by desilylation. The segments, 3a and 4, were synthesized from D-glucose and 2-deoxy-L-fucose.

A new strategy for sustainable polymer recycling using an enzyme: poly(ε-caprolactone)

Enzymatic degradation and polymerization using an enzyme were analyzed with respect to the establishment of a sustainable chemical recycling system for poly(e-caprolactone) (PCL) which is a typical biodegradable synthetic plastic. As the typical example, the enzymatic degradation of PCL having an M n of 110 000 using lipase CA in toluene containing water at 70°C for 6 h afforded a unimodal oligomer having an M n of about 1000 quantitatively consisting of linear and cyclic oligomers. This was again polymerized by lipase CA in toluene under restricted water concentration to produce PCL having an M n of greater than 70 000.