(3R,4R)-欧洲榆小蠹聚集信息素的合成

欧洲榆小蠹原产欧洲榆树生长区,美国、加拿大及非洲北部也有分布,其成虫及幼虫蛀食榆树皮,并能传播榆疫病,从而影响榆树生长．Ｐｅａｒｃｅ等分离出其聚集信息素并鉴定其分子结构为（—）４甲基３庚醇（１）［１］,Ｍｏｒｉ等研究结果确定出其天然产物构型为...     

Chemoenzymatic synthesis of (3R,4S)- and (3S,4R)-3-methoxy-4-methylaminopyrrolidine

An efficient and a convenient enantioselective synthesis of (3R,4S)-3-methoxy-4-methylaminopyrrolidine has been carried out by a lipase-mediated resolution protocol. This method describes the preparation of (±)-1-Cbz-cis-3-azido-4-hydroxypyrrolidine starting from commercially available diallylamine followed by ring-closing metathesis (RCM) via S_N2 displacement reactions. Pseudomonas cepacia lipase immobilized on diatomaceous earth (Amano PS-D) provides (3R,4S)-11 and (3S,4R)-12 in an excellent enantiomeric excess.     

A practical synthesis of (3R,4R)-N-tert-butoxycarbonyl-4-hydroxymethylpyrrolidin-3-ol

The title compound (+)-, required for production of transition state analogue inhibitors of enzymes involved in T-cell-dependent disorders, was synthesized in five steps. A 1,3-dipolar cycloaddition of the nitrone formed from formaldehyde and N-benzylhydroxylamine to diethyl maleate gave the racemic cis-isoxazolidine (+/-)-. Reduction of the N-O bond of this compound gave pyrrolidone (+/-)- in excellent yield. A very efficient enzymic resolution of this racemic product led to the title enantiomer (+)-. This route employs only one chromatographic purification.     

Synthesis of enantiomerically pure (3R,4R,5R)-4-hydroxy isoleucine lactone

A short four-step synthesis of (3R,4R,5R)-4-hydroxyisoleucine lactone with total control of stereochemistry is reported, the key intermediate being the didehydroamino acid derivative arising from an aldol dehydration reaction between a glycine anion equivalent and butan-2,3-dione.     

Novel,short, stereospecific synthesis of lyxo-(2R,3R,4R)-phytosphingosine and erythro-(2R,3S)-sphingosine

Lyxo-phytosphingosine and erythro-sphingosine have been elaborated from a common intermediate. The key step in the reaction sequence involves stereo- and regiospecific functionalization of an olefin by intramolecular nucleophilic sulfinyl group participation.     

Full stereochemical understanding in a new (2R,3R,4R)-4-hydroxyisoleucine synthesis

We present the crystal and molecular structures of 2,3,6,7,8,8a-hexa­hydro-6,8-methano-7,7,8a-tri­methyl-3-(1-methyl-2-oxo­propyl­idene)-5H-1,4-benzoxazin-2-one, C₁₆H₂₁NO₃, (III), and 2,3,6,7,8,8a-hexa­hydro-3-(2-hydroxy-1-methyl­propyl)-6,8-methano-7,7,8a-tri­methyl-5H-1,4-benzoxazin-2-one, C₁₆H₂₅NO₃, (V). These compounds are two of the four key intermediates in our synthetic route to (2R,3R,4R)-4-hydroxy­isoleucine. The two structures provide a full understanding of the stereochemistry in successive steps. This synthesis was based on a new optically pure chiral oxazinone auxiliary derived from (1R,2R,5R)-2-hydroxy­pinan-3-one.     

Asymmetric synthesis of (2S,3R,4R)-ethoxycarbonylcyclopropyl phosphonoglycine

The synthesis of enantiomerically pure (2S,3R,4R)-ethoxycarbonylcyclopropyl phosphonoglycine is described, the key-step involving 1,4-addition of a chiral enolate to ethyl 4-bromo-crotonate.     

Asymmetric syntheses of (1r,3R,4S)- and (1s,3R,4S)-(3,4-difluorocyclopentyl)-alanine derivatives

By employing a sequence of epoxide opening, asymmetric alkylation, and fluorination, polyfluorinated cyclopentylamino acids with defined stereochemistries were prepared.     

Stereoselective Synthesis of (3R, 4S)-N-Boc-Statine

A stereoselective synthesis of (3R, 4S)-N-BOC-Statine was achieved through an aldol condensation of N-BOC-L-Leucinal with a boron enolate of an appropriate chiral auxiliary described by Evans.     

Synthesis of (3S,4R)-bengamide E

（3S,4R）-Bengamide E（2） was synthesized starting from D-glucono-δ-lactone（3） and the key deoxygenation step from 13 to 15 was achieved by the application of NaBH₃CN and ZnI₂.Compared with natural bengamide E（1）,the synthetic compound（35,4R）-bengamide E（2） was inactive against the cell growth of HUVEC and cancer cells.These data represent the significance of the stereochemistry at C-3 and C-4 of bengamides for structural recognition and binding with the target（s）.     

Total synthesis of (3R, 4S)-4-hydroxylasiodiplodin

Abstract

An alternative and concise total synthesis of (3?R, 4S)-4-Hydroxylasiodiplodin has been reported from inexpensive and commercially available 6-heptenal and Orsellinic acid starting materials. The key steps involved in the synthesis are Wittig reaction, Sharpless epoxidation, Yamaguchi esterification and ring-closing metathesis (RCM).     

Studies on the transformation of nitrosugars into iminosugars III: synthesis of (2R,3R,4R,5R,6R)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol and (2R,3R,4R,5R,6S)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol

A divergent synthesis of the two novel polyhydroxylated azepanes (2R,3R,4R,5R,6R)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol and (2R,3R,4R,5R,6S)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol from d-mannose is described. The method involves a Henry reaction between dimethyl-tert-butylsilyl 2,3-O-isopropylidene-α-d-lyxo-pentodialdo-1,4-furanoside and 2-nitroethanol followed by a reductive ring closure of the resulting epimeric nitro aldols. Glycosidase inhibition tests showed that (2R,3R,4R,5R,6S)-2-(hydroxymethyl)azepane-3,4,5,6-tetraol exhibits a weak but selective inhibition against α-l-fucosides.     

(2R，3R)-和(2S，3S)-2-(4-羟基-3-甲氧基)-3-羟甲基-1，4-苯并二氧六环-6-醛的对映选择性合成

1,4-苯并二氧六环木脂素类天然产物多数具有增加胆碱乙酰化酶和抗肝毒等活性 ,其活性主要源于 1 ,4-苯并二氧六环官能团 [1] . 1 ,4-苯并二氧六环木脂素的消旋全合成已有报道 [2 ] ,但其不对称合成还是空白[3] .我们发展了一条对映选择性合成 1 ,4-苯并二氧六环木脂素的简捷有效的路线 .基于前面的工作 [4 ] ,我们发现 1 ,4-苯并二氧六环醛类衍生物是合成此类天然产物的关键中间体 ,选择 2 - (4-羟基- 3-甲氧基 ) - 3-羟甲基 - 1 ,4-苯并二氧六环 - 6-醛 (1 )作为目标分子 ,其合成路线如下 :Reagents and conditions:( ) Me OH,H2 SO4,9…     

Preparation of (2R, 3R, 4R)-3-hydroxy-2,4,6-trimethylheptanoic acid via enzymatic desymmertization

Synthesis of a unique fatty acyl unit to build the N-terminus of callipeltin A and homophymine B is described. Our approach to access (2R, 3R, 4R)-3-hydroxy-2,4,6-trimethylheptanoic acid uses enzymatic hydrolysis for the desymmetrization of achiral acetate, followed by diastereoselective Roush crotylboration and Wittig olefination for the backbone construction.     

Convenient synthesis of （2S,3R,4R,5S,6R）-2-（3-（4-ethylbenzyl）-4- chlorophenyl）-6-（hydroxymethyl）-tetrahydro- 2H-pyran-3,4,5-triol

A convenient approach for the preparation of （2S,3R,4R,5S,6R）-2-（3-（4-ethylbenzyl）-4-chlorophenyl）-6-（hydroxymethyl）- tetrahydro-2H-pyran-3,4,5-triol I is developed. The target compound via four steps is synthesized from 4-bromo-2-（bromomethyl）- 1-chlorobenzene and the isomers of undesired ortho-products were avoided during the preparation.     

Stereoselective synthesis of (2R,3S,4S,5R)-trans-3,4-dihydroxy-5-(4-fluorophenoxymethyl)-2-(1-N-hydroxyureidyl-3-butyn-4-yl)tetrahydrofuran and (2R,3S,4S,5R)-trans-5-ethynyl-2-(4-fluorophenoxymethyl)-3,4-O-isopropylidene tetrahydrofuran from mannose diacetonide

Stereoselective synthesis of pharmaceutically interesting chiral tetrahydrofurans starting from mannose diacetonide is reported. A 1,4-diol system derived from mannose diacetonide, through a Mitsunobu reaction was stereospecifically cyclized to give chiral tetrahydrofurans. Both the C-1 and C-4 centers of d-mannose are successfully exploited to install the requisite side chains.     

An asymmetric synthesis of the novel H3 agonist (+)-(3R,4R)-3-(4-imidazolyl)-4-methylpyrrolidine dihydrochloride (Sch 50971)

A short, high yielding, enantioselective synthesis of the novel H₃ agonist Sch 50971 1 is described. The key enantiodifferentiating step is the 1,4-addition of a chiral N-propionyloxazolidinone to a nitroolefin.