Synthesis of Ethyl (2RS,3SR)-1-Tosyl-3-Vinylazetidine-2-carboxylate and ethyl (2RS,E)-3-ethylidene-1-tosylazetidine-2-carboxylate (=rac-ethyl N-tosylpolyximate)

The synthesis of 3-ethylideneazetidine-2-carboxylic acid (=polyoximic acid; 3 ) is a approached in two different ways leading to potential precursors of 3 . The first way involved a ring closure to a vinyl-subsatituted azetidin. Thus, Ireland-Claisen rearrangement of the Boc-glycinates 6 and 10 of (Z)- and (E)-2-butene-1,4-diol afforded, after exchange of the N-protecting groups, the isomeric 2-(tosylamino)-3-vinylbutanolides 13 and 14 with high stereoselectivity. Only the cis-isomer 14 could be further transformed to 3-(bromomethyl)-2-(tosylamino)-4-pentenoate 17 , and in a smoth cyclization with K₂CO₃, to trans-3-vinylazetidtene-2-carboxylaze 18 (Scheme 2). In the second approach, the 3-ethylidene isomer 19 of 18 was obtained more directly by a [2+2] cycloaddition, together with the two isomers 23 and 24 , from methlallene 20 and (tosyliminno)acetate 21 (Scheme 3). The main product of this reaction was, however, 2-(tosylamino)-4-hexinoate 22 , the product of an ene reaction.     

New route to (3RS) (5R) (5-2H)- and (3RS) (5S) (5-2H)-mevalonolactones

The synthesis of mevalonolactone stereospecifically labeled at carbon 5 is described combining chemical reactions with an enzymatic reduction step.     

Enantioselective transesterification of (RS)-1-chloro-3-(3,4-difluorophenoxy)-2-propanol using Pseudomonas aeruginosa lipases

Lipases from the bacterial strain, Pseudomonas aeruginosa, isolated from the soil by enrichment techniques, are assessed for the enantioselective transesterification of (RS)-1-chloro-3-(3,4-difluorophenoxy)-2-propanol (rac-CDPP) to (R)-1-chloro-3-(3,4-difluorophenoxy)-2-propanol, a key intermediate in the synthesis of the chiral drug (S)-Lubeluzole. The lipases produced by the organism yielded the (S)-ester and the (R)-alcohol as the remaining substrate with an excellent yield (>49.9%) and almost complete enantioselectivity (ee >99.9%) in the presence of vinyl butyrate as an acyl donor in an organic medium. In contrast, purified and expensive commercially available lipases of Candida rugosa and porcine pancreas achieved much lower conversion with enantioselectivities of 15% and 5%, respectively. A well-mixed (∼1000 rev min⁻¹) batch reactor having the aqueous phase finally dispersed in hexane was used in these studies. The parameters of the transesterification reaction were optimized and the optimal concentrations of rac-CDPP and vinyl butyrate were found to be 5 and 150 mM at 30 °C. A preparative-scale reaction yielded the (S)-ester at 42% conversion and ee >99%.     

Extraction of palladium(II) with (RS)-1-[2-(2,4-dichlorophenyl)pentyl]-1H-1,2,4-triazole from nitric acid solutions

Russian Journal of General Chemistry - Palladium(II) is efficiently extracted with (RS)-1-[2-(2,4-dichlorophenyl)pentyl]-1H-1,2,4-triazole from 0.2–5.0 M HNO3 solutions and can be selectively...     

RS－联萘酚膦酰胺晶体结构及与其SS体分子力学计算结果的比较

测定了Ｏ，Ｏ（２，２′－联萘基）－Ｎ－（α－苯基乙基）膦酰胺（简称联萘酚膦酰胺，ＤＮＰＡ）ＲＳ体与乙醇形成的分子化合物晶体结构。晶体学数据为：Ｃ＿（２８）Ｈ＿（２２）ＮＯ＿３Ｐ·Ｃ＿２Ｈ＿５ＯＨ，Ｍｒ＝４９７．５，单斜晶系，Ｐ２＿１空间群，α＝９．３５９（２），ｂ＝１２．８０６（３），ｃ＝１１．６４１（Ａ），β＝１１１．６２（３）°，Ｚ＝２，Ｖ＝１２９４．０（５）（Ａ）３，Ｄｃ＝１．２７７ｇ／ｃｍ￣３，ＭｏＫａ（λ＝０．７１０７３Ａ）射线，μ＝０．１３６ｍｍ￣（－１），可观测数据３８７１个，Ｆ（０００）＝５２４，Ｒ＝０．０３５，Ｒｗ＝０．０４２。分子间以氢键相连接。ＲＳ体晶体结构与分子力学方法计算得到的ＳＳ体构象比较，发现这一对非对映体构象的差别由联萘基一边的构型决定。     

Preparation of (RS)-5-Amino-3-carboxypentanoic Acid (1)

(RS)-5-Amino-3-carboxypentanoic acid (1) was prepared by a Wittig reaction of N-benzoylglycinal (3) with the phosphorane (4), followed by catalytic hydrogenation and acid hydrolysis.