Synthesis of sialic acid derivatives based on chiral substrate-controlled stereoselective aldol reactions using pyruvic acid oxabicyclo[2.2.2]octyl orthoester
accomplished based on substrate-controlled asymmetric aldol reactions between sterically complicated aldehydes easily prepared from commercially available carbohydrates and a novel pyruvic acid oxabicyclo[2.2.2]octyl orthoester. Systematic aldol reactionstudies using chiral aldehydes revealed that α,β,γ-benzyloxy-substituted aldehydes with an α,β-anti relative configuration preferentially provided the
唾液酸及其类似物的合成是基于易于从市售碳水化合物制备的空间复杂醛与新型丙酮酸草酸双环[2.2.2]辛基原酸酯之间的受底物控制的不对称醛醇缩合反应完成的。使用手性醛的系统羟醛反应研究表明,具有α,β-反相对构型的α,β,γ-苄氧基取代的醛优先为Felkin产物提供具有高非对映选择性的4,5-抗构型。具有α,β-顺式排列的α,β,γ-苄氧基取代的醛中的相对β,γ构型对醛醇缩合反应中形成的立构中心的非对映选择性具有次要作用。syn - β ,γ-抗苄氧基醛显示出比α,β- syn - β ,γ- syn苄氧基醛更高的非对映选择性,从而生成Felkin产物。
Practical Synthesis of Methyl Z-2-(N-Acetylamino) but-2-Enoate. An Intermediate to D- and L-2-Aminobutyric Acid
作者:William A. Nugent、John E. Feaster
DOI:10.1080/00397919808006866
日期:1998.5
Abstract Treatment of inexpensive L- or DL-threonine methyl ester with acetic anhydride and either pyridine or anhydrous sodium acetate at reflux results in dehydration yielding the N,N-diacetamide of the title compound in >80% yield. Monodeacetylation of the diacetamide with 0.1 equiv of triethylamine in methanol affords the title monoacetamido derivative 1 in nearly quantitative yield.
Asymmetric synthesis. Practical production of D and L threonine. Dynamic kinetic resolution in rhodium and ruthenium catalyzed hydrogenation of 2-acylamino-3-oxobutyrates.
Enantioselective syntheses of D and L threonine are described. Racemic methyl and ethyl 2-acylamino-3-oxobutyrate 1 were synthesized from the corresponding acetoacetates 6 and then hydrogenated stereoselectively via dynamic kinetic resolution with various chiral P * P Rh (I) 8 and Ru (II) 10 catalysts to give syn optically active alcohols which could be converted by hydrolysis and treatment with propylene oxide into threonine. The best results were obtained using (-) CHIRAPHOS Ru and (+) BINAP Ru as catalysts, in the hydrogenation step leading respectively to D threonine (ee: 99 %) and L threonine (ee: 94 %) in 26-34 % overall yields.
Structure Elucidation of Sch 20562, a Glucosidic Cyclic Dehydropeptide Lactone. The Major Component of W-10 Antifungal Antibiotic.
作者:ADRIANO AFONSO、FRANK HON、RAY BRAMBILLA
DOI:10.7164/antibiotics.52.383
日期:——
glucosidic cyclic dehydrononapeptide lactone 1 are: an N-terminal (D)-beta-hydroxymyristyl unit, three D-amino acid units, two (E)-alpha-aminocrotonyl units, and an O-alpha-D-glucosyl-N-methyl-L-allo-threonine unit. The structure determination of 1 utilized the selective cleavage of the dehydropeptide units by ozonolysis to form fragments that were sequenced by mass spectrometry. The stereochemistry of the
Total Synthesis of a Structurally Complex Tetrasaccharide Repeating Unit of <i>Vibrio cholerae</i> O43
作者:Ankita Paul、Diksha Rai、Kabita Pradhan、Preeti Balhara、Amar Kumar Mishra、Suvarn S. Kulkarni
DOI:10.1021/acs.orglett.3c02430
日期:2023.9.1
Herein we report the first total synthesis of a densely functionalized tetrasaccharide repeatingunit of Vibrio cholerae O43, which contains rare deoxy amino sugars d-quinovosamine and d-viosamine attached with the rare amino acid N-acetyl-l-allothreonine. Synthesis of orthogonally protected rare sugars and unnatural amino acid building blocks, stereoselective construction of three consecutive 1,2-cis