Noriyuki Nakajima

Synthetic studies of proanthocyanidins. Part 2: Stereoselective gram-scale synthesis of procyanidin-B3 ☆

Abstract A stereoselective synthesis of procyanidin-B3, a condensed catechin dimer, is described. Condensation of benzylated catechin with various 4-O-alkylated flavan-3,4-diol derivatives as an electrophile in the presence of a Lewis acid led to protected procyanidin-B3 and its diastereomer. In particular, the reaction using (2R,3S,4S)-3-acetoxy-5,7,3′,4′-tetrabenzyloxy-4-(2″-ethoxyethoxy)flavan as an electrophile in the presence of TMSOTf at −78°C afforded octa-O-benzylated procyanidin-B3 with high levels of stereoselectivity and in excellent isolation yields. Furthermore, we succeeded in a stereoselective gram-scale synthesis of protected procyanidin-B3.

PREPARATION OF NITRILES FROM PRIMARY AMIDES UNDER SWERN OXIDATION CONDITIONS

Abstract In order to establish a mild conversion method of primary amides to nitriles, various types of carboxamides were treated under Swern oxidation conditions, (COCl) 2 -DMSO and Et 3 N, as a dehydrating agent to obtain desired nitriles in 75–96% yields.

Heteronuclear single-quantum coherence nuclear magnetic resonance (HSQC NMR) characterization of acetylated fir (Abies sachallnensis MAST) wood regenerated from ionic liquid.

An ionic liquid, 1-butyl-3-methylimidazolium chloride ([Bmim]Cl), was used to dissolve Japanese fir (Abies sachallnensis MAST) wood. Milled woods prepared by planetary ball-milling for 8 h dissolved completely in [Bmim]Cl at 100 °C in 2 h. The dissolved woods were then subjected to in situ acetylation, and the fully acetylated woods were regenerated from [Bmim]Cl. (1)H-(13)C correlation heteronuclear single-quantum coherence (HSQC) nuclear magnetic resonance (NMR) experiments were successfully conducted with the acetylated woods in dimethyl sulfoxide (DMSO)-d(6). The acetylated lignin and polysaccharide signals dispersed reasonably well on the 2D spectra. Characterization of the NMR signals for the whole cell-wall components, including lignin, cellulose, and hemicelluloses, was achieved by comparison with isolated lignin and commercial cellulose and hemicelluloses (arabinoxylan, galactomannan, and glucomannan). The procedure used here is applicable for the characterization of cell-wall components in various plant biomasses.

Activated dimethyl sulfoxide dehydration of amide and its application to one-pot preparation of benzyl-type perfluoroimidates

Abstract Various types of primary amides were treated under an activated dimethyl sulfoxide (DMSO) species, (COCl)2–DMSO and Et3N, as a dehydrating agent to obtain nitriles in excellent yield. This dehydration system was extended to a one-pot preparation of perfluoroimidates via volatile perfluoronitriles from perfluoroamides. Fifteen benzyl-type perfluoroimidates can be prepared in 70–90% yield as more stable imidates than the trichloro analogue. MPM- and DMPM-perfluoroimidates can be used to protect alcohols in place of the trichloroacetimidate with excellent chemical properties and in comparable yields.

Synthetic studies of proanthocyanidins. Part 3: Stereoselective 3,4-cis catechin and catechin condensation by TMSOTf-catalyzed intramolecular coupling method

Abstract TMSOTf-catalyzed intramolecular condensation for catechin and epicatechin units are described. A potential electrophile and a nucleophile were connected with diester linkers and TMSOTf-catalyzed condensation was examined. In comparison with intermolecular catechin and catechin condensation, the intramolecular condensation required high reaction temperature and reversed 3,4-cis product was obtained. The condensed product was transformed into the natural 3,4-cis (+)-catechin-(4β→8)-(+)-catechin dimer.

Synthetic studies of proanthocyanidins. Highly stereoselective synthesis of the catechin dimer, procyanidin-B3.

A stereoselective synthesis of benzylated procyanidin-B3, a condensed catechin dimer, is described. Condensation of 5,7,3′,4′-tetrabenzylcatechin with (2R,3S,4S)-5,7,3′,4′-tetrabenzyloxy-3-acetoxy-4-methoxyflavan as an electrophile in the presence of TiCl4 led to octabenzylated procyanidin-B3 stereoselectively.

Synthetic Studies of Proanthocyanidins. Part 5. Highly Stereoselective Synthesis and Inhibitory Activity of Maillard Reaction of 3,4-trans Catechin and Epicatechin Dimers, Procyanidin B1, B2, B3, B4 and Their Acetates

TMSOTf-catalyzed condensation of a potential electrophile with a nucleophile was achieved with a high level of 3,4-trans condensation, and we succeeded in the stereoselective synthesis of procyanidin B2 and its peracetate. Studies on the inhibitory activity of the Maillard reaction of four 3,4-trans series of catechin and epicatechin dimers, procyanidin Bl, B2, B3 and B4, and their peracetates were also carried out.

Novel synthesis of (+)-hydantocidin based on the plausible biosynthetic pathway

Abstract The title synthesis was examined by employing two synthetic schemes which feature N,O-spiroketal formation as a key step. Although the stepwise synthesis starting with D-fructose and proceeding through the D-psicose derivatives successfully produced a mixture of (+)-hydantocidin (1) and its C5-epimer [(−)-5-epihydantocidin (2)] the one-step synthesis utilizing D-isoascorbic acid and urea as starting materials was found to give 2 more selectively than 1. Studies on the key N,O-spiroketal formation and epimerization between 1 and 2 were also carried out to explore some novel aspects of the obtained results.

Toward the Assignment of Liposidomycin Stereochemistry: Synthesis of 1,4-Diazepan-3-one Analogues by Reductive Amination Approach

Toward the assignment of liposidomycin stereochemistry, a stereocontrolled synthesis of the liposidomycin diazepanone ring system and two precursors, has been achieved. The NMR coupling constants of a 5-phenyl model compound closely related to the liposidomycin diazepanone degradation product.

Synthetic studies of proanthocyanidins. Part 4. The synthesis of procyanidin B1 and B4: Tmsotf-catalyzed cyclization of catechin and epicatechin condensation

Highly stereoselective synthesis of 3,4-trans series of (+)-catechin and (-)-epicatechin dimers under intramolecular condensation is described. Intramolecular condensation achieved an equimolar amount of coupling with 3,4-trans stereoselectivity and we succeeded in the synthesis of two 3,4-trans natural procyanidins, procyanidin-B1and B4.