Both enantiomers of carvone are versatile starting materials for total syntheses of a number of natural products such as sesquiterpenoids, diterpenoids, alkaloids and so on, taking advantage of a variety of transformations of enone and isopropenyl moieties along with easy availability of both enantiomers. In this review article, total syntheses of cyclic sesquiterpenoids starting from carvone since 2000 have been compiled according to structural types, hydrindane-, decalin-, guaian-, spiro- and bridged-sesquiterpenoids.
Glycoproteins, naturally occurring hybrid macromolecules composed of a protein and oligosaccharide chains, show various important biological activities in medical and pharmaceutical sciences. In spite of strong demand for glycoproteins having a definite structure, its specific preparation is still an unsolved problem in the field of synthetic organic chemistry. Here we propose an efficient strategy for synthesis of glycoproteins via 1,2-oxazoline derivatives as glycosyl donors for enzymatic transglycosylation. We developed a facile method for synthesis of sugar oxazoline derivatives by the intramolecular dehydration reaction of the corresponding unprotected 2-acetamido-sugars in water using 2-chloro-1,3-dimethylimidazolinium chloride (DMC) as a dehydrating agent. According to this method, disialo-oligosaccharides can be converted to the corresponding 1,2-oxazoline derivatives in high yields without protecting the hydroxy groups. A transglycosylation of the resulting oxazoline derivative to the GlcNAc moiety on a protein has successfully been demonstrated catalyzed by a mutant of N-acetylglucosaminidase-M, giving rise to a monodispersed disialo-type glycoprotein.
Dipeptidyl peptidase IV (DPP-4) inhibitors have built trust through both efficacy and safety in the treatment of type 2 diabetes and have increased the prescription both in Japan and overseas. Among them, teneligliptin has potent and selective DPP-4 inhibitory activity, has an elimination half-life of 24.2 h in human plasma, and is eliminated via excretion from the kidney and metabolism involving some metabolizing enzymes. Therefore, teneligliptin provides postprandial blood glucose-lowering effects that are sustained throughout the day by once-daily treatment and has unnecessary dosage regulation in patients with renal impairment. In this article, discovery and preferable profiles of a novel DPP-4 inhibitor, teneligliptin, discovered first in Japan, are described. By comparative studies of the binding modes of launched DPP-4 inhibitors in the active site, the unique binding mode of teneligliptin in DPP-4 has been revealed.
Dendralenes, acyclic cross-conjugated polyenes having a nonplanar structure, containing 1,3-dithiole (DT) rings are of considerable interest as novel multi-stage redox systems for potential application to electrical conducting, magnetic, electrochromic, and nonlinear optical materials. In the present review, we focus on the electronic structures of DT[n]dendralenes and their π-extended compounds in which phenylene, thienylene, furylene, or tetrathiapenthalene (TTP) moieties are inserted. DT[n]dendralenes (n=3 and 4) employ a non-planar structure due to the steric effect, and cyclic voltammetry (CV) suggested multi-redox behavior of extended vinylogues. Their electronic structure and conjugation pathway in cationic states are strongly affected by the aromaticity of the inserted aryl groups. As for dication of DTdendralenes with two thiophene spacers, the electronic structures depend on their substituents. In the cationic states of DTdendralenes with two thiophene spacers, the positive charges are mainly located on the outer TTF moieties. On the other hand, cationic species of DTdendralene having two TTP moieties, the positive charges are distributed mainly in the outer branching vinylogues.
In this paper, molecular activation of sulfur functional groups, including the γ-sulfur-stabilization effect on propargyl cations generated from the corresponding alcohols and sulfur-activated cyclizations of oxygen- and nitrogen-tethered 1,6-diynes triggered by some useful transformations, is described. With respect to propargylation, Lewis acid-catalyzed C-C, C-O and C-N bond formations in nitromethane or nitromethane—H2O have been developed. Moreover, C-N bond formation for the synthesis of pyrazoles via intra- and intermolecular cyclizations is investigated. Thioamides underwent cycloaddition with allenyl cation intermediates, while this reaction did not occur with propargyl cations. In sulfur-activated cyclizations, nucleophile-triggered cyclization provided alkoxymethyl-, aryloxymethylfurans and tanshinon derivatives. Furthermore, the alkynylation- and amination-triggered cyclizations of 1,6-diynes are also described.
Borate complexes that contain tridentate ligands tris(o-oxyaryl)methanes and -silanes were synthesized. These complexes had a cage-shaped structure around a boron center. The geometry of the structure determined the properties of the borates in which ligands were consistently bound to the metal center by chelation. Theoretical calculations suggested that the cage-shaped borates had a large dihedral angle (Cipso-O-B-O) compared with open-shaped borates. The large angle leads to a greater Lewis acidity for cage-shaped borates. Substitution of a bridgehead Si for a bridgehead C decreased the Lewis acidity due to its smaller dihedral angle. The introduction of electron-withdrawing groups on the aryl moieties in the cage-shaped framework increased the Lewis acidity. The cage-shaped borates effectively catalyzed some organic transformations more than the open-shaped borate B(OPh)3. Selective recognition of aromatic aldehyde over aliphatic aldehyde was accomplished in a catalytic manner by using cage-shaped borates with a π-pocket.
One of the important research topics in the synthesis of pharmaceuticals and fine chemicals is to convert homogeneous reactions to heterogeneous versions by immobilization of metal species on polymer or inorganic supports. The oxidation state of the metal species can affect the character and reactivity of the catalyst. Recently, chemists have gained excellent techniques to control particle size and oxidation state of metal species, which has led to the development of new heterogeneous catalysts for organic reactions.
Although alcohols and phenols are among the most important fundamental chemicals, their synthetic methods are limited. Those starting from hydrocarbons are attractive in view of green chemistry. Herein reviewed is the progress in catalytic hydroxylation at inert C-H bonds with metal complexes or upon photo-irradiation.
In the prebiotic era, information-coding nucleic acids, RNAs, are assumed as key players for the origin of life. How did RNA components, ribonucleotides, emerge in the prebiotic era? Recently, a plausible synthetic pathway of pyrimidine ribonucleotides has been reported. In this review, the brief history and recent progress in this field are introduced.