Baker's yeast mediated reduction of substituted acenaphthenequinones: Regio-and enantioselective preparation of mono-hydroxyacenaphthenones

Baker's yeast mediated reduction of acenaphthenequinone within 4-10 h afforded mono-hydroxyacenaphthenone mainly with low enantioselectivity, the substrate and mono-hydroxyacenaphthenone product almost converted to dihydroxyacenaphthene after 48 h. By control of the reaction time and in the presence of DMF as co-solvent, the reduction of 6-substituted acenaphthenequinones under vigorous agitation afforded the corresponding 2-hydroxyacenaphthenones in 24-84% yields with 10-93% ee.

Highly Efficient Regio- and Stereoselective Synthesis of β-（1 →6）-Branched β-（1 →3）-Linked Glucohexaose and Its Analogue

A β-（1→）6）-branched β-（1→）3）-linked glucohexaose （1） and its lauryl glycoside （2）, present in many biologically active polysaccharides from traditional herbal medicines such as Ganoderma lucidum, Schizophyllum commune and Lentinus edodes, were highly efficiently synthesized. Coupling of 2,3,4,6-tetra-O-benzoyl-β-D-glucopyranosyl- （1--）3）-2-O-benzoyl-4,6-O-benzylidene-a-D-glucopyranosyl trichloroacetimidate （7） with 3,6-branched acceptors 8 and 12 gave β-（1→）3）-linked pentasaccharides （9） and （13）, then via simple chemical transformation 4＇,6＇-OH pentasaccharide acceptors 10 and 14 were obtained. Regio- and stereoselective coupling of 3 with 10 and 14 gave β-（1→）3）-linked hexasaccharides （11） and （15） as the major products. Deprotection of 11 and 15 provided the target sugar 1 and 2. Thus, a new method for the preparation of this kind of compounds was developed.

Regio-and Stereo-selective Bioreduction of Diketo-n-butylphosphonate by Baker's Yeast

A regio- and stereo-selective reduction of diketo-n-butylphosphonates by baker's yeast was reported. The chemical yield and ee value of these reactions are highly dependent on the structure of substrates. The resulting optical active hydroxy^alkanephosphonates can be used as chirons for the synthesis of polyfunctional organophosphorus compounds. As useful building block, a series of α,β-unsaturated ketones bearing chiral hydroxy group in addition to trifluoromethyl moiety was prepared via the Horner-Wadsworth-Emmons (HWE) reaction of the biotransformation products.

不对称三烯胺催化的发展

手性胺可以与多不饱和羰基化合物原位生成三烯胺中间体,其给电子效应根据插烯规则可通过共轭不饱和体系传递,进而提高三烯胺体系的HOMO能量,并能够在远端β,ε-或δ,ε-位与多种缺电子烯烃发生Diels-Alder环加成反应。采用这种合成策略,可以制备许多结构多样和复杂的环状手性化合物。这种策略除了能够高效地在羰基化合物远端直接实现官能团化,更重要的是ε-反应位点即使距离催化剂手性中心达七个键之远,仍能获得优秀的立体选择性控制,这在不对称合成中具有重要的研究价值。本文将总结近年来不对称三烯胺催化机制的发现及发展,重点介绍2,4-二烯醛、多种二烯酮、含羰基芳香化合物经由三烯胺、交叉共轭三烯胺或形式三烯胺进行的不对称反应,并对手性胺催化的进一步应用进行展望。

Synthesis of Analogues of the Antitumor (1→6)-Branched (1→3)-Glucohexaose

b-D-Glcp-(13)-[b-D-Glcp-(16)-]a-D-Manp-(13)-b-D-Glcp-(13)-[b-D-Glcp-(16)-]D-Glcp (18) and b-D-Glcp-(13)-[b-D-Glcp-(16)-]a-D-Manp-(13)-b-D-Glcp-(13)-[b-D-Glcp-(16)-]b-D-Glcp-D-(13)-Glcp-1OMe (29) were synthesized as the analogues of the immunomodulator b-D-Glcp-(13)-[b-D-Glcp- (16)-]a-D-Glcp-(13)-b-D-Glcp-(13)-[b-D-Glcp-(16)-]D-Glcp through coupling of trisaccharide donors 9 with trisaccharide acceptor 16 and tetrasaccharide acceptor 27 followed by deprotection, respectively.

A New and Practical Procedure for the Preparation of the Glucohexatose Phytoalexin Elicitor

The phytoalexin elicitor β-(1→3)-branched β-(1→6)-linked glucohexatose has been regie- and stereospeciflcally synthesized by coupling of the 3, 6-branched gluco-trisaccharide Schmidt reagent 10 with a mixture of multiol 3,6-branched gluco-trisac-charides 13 which consists of free 5,6'-OH trisaccharide, free 5,2' ,6'-OH trisaccharide, free 5,3' ,6'-OH trisaccharide and so on. The compounds 10 and 13 were prepared from 1,2:5,6-di-O-isopropylidene-α-D-glucofuranose, 2, 3, 4, 6-tetra-O-ben-zoyl-α-D-glucopyranosyl trichloroacetimidate, and 2,3,4,6-te-tra-O-acetyl-α-D-glucopyranosyl trichloroacetimidate through re-gio- and stereoselective manners.

Facile and Effective Synthesis of Glucopyranosyl Oligosacchardes with Alternative (1→3)-α- and -β-Linkages in the Presence of C-2 Ester Capable of Neighboring Group Participation

Coupling of acetylated α-(1→3)-linked glucobiosyl trichloro-acetimidate with acetylated α-(1→3)-linked glucobioside acceptor gave a β-linked tetrasaccharide, while coupling of acetylated β-(1→3)-linked glucobiosyl trichloroacetimidate with acetylated β-(1→3)-linked glucobioside acceptor gave an α-linked tetrasaccharide in spite of the C-2 neighboring group participation. Two hexasaccharides with alternative (1→3)-α- and -β-linkges were synthesized by these reactions via remote control exerted by the glycosylation bond in either donor or acceptor.