有机立体化学中手性构型教学方法的探讨

用R/S构型命名法描述手性分子的构型教学是有机化学教学的一个重点和难点。针对伞形式、锯架式、纽曼式、费歇尔投影式这四种典型的立体表达式中的手性碳构型的确定方法进行探讨并提出了简便的判定方法。     

四种投影式中手性碳原子的R/S构型判断

手性碳原子的R/S构型判断,是立体化学中非常基础和重要的教学内容之一。文章就手性碳的四种投影式的R/S构型判断方法进行归纳和总结。     

手性碳R/S构型判断的教学设计

本文研究设计了两种巧妙判断手性碳R/S构型的简便方法,方便记忆,显著地节省了学生的判断时间,判断结果准确率高,解决了教学难点问题,教学效果好。     

2-吗啉醇盐酸盐的手性合成及晶体结构

以单一手性纯试剂与外消旋体化合物反应,合成了4对手性纯化合物(2R,3R,5S)-2-吗啉醇盐酸盐及其对映体(2S,3S,5R)-2-吗啉醇盐酸盐。其结构经IR、1HNMR、13CNMR及ESI-MS表征,利用X-射线单晶衍射法测定了其中一对对映体的空间构型。利用吗啉六元环椅式构象比船式构象稳定的特性,系统探讨了以构象稳定性促进目标化合物构型形成的手性化合物合成机制及规律,为手性化合物合成方法提供了新启示。     

手模型在有机立体化学教学中的应用

介绍了手模型在有机分子构象表示和构型判断方面的应用。在构象表示方面,采用手模型表示环己烷构象,能够快速掌握环己烷稳定构象的结构特征。在构型判断方面,提出了“右手定则”,可快速判断手性分子透视式和Fischer投影式的R/S构型。对手模型辅助判断Diels-Alder反应等顺式加成反应产物构型进行了详细讨论;并提出了判断电环化反应及其逆反应产物构型的“双手旋转定则”。     

新的手性膦配体的合成及其在苯乙烯不对称氢甲酰化反应中的应用

以甘露醇为原料合成了两个新的手性膦配体,并用这些新的手性膦配体和醋酸钯原位生成的催化剂体系催化苯乙烯的不对称氢甲酰化反应,当配体为手性膦氧配体(DDPPIO)时得到S构型的2-苯基丙醛的e.e.为21.9％,用手性膦硫配体(DDPPIS)作配体时得到S构型的2-苯基丙醛的e.e.11.2％。     

确定手性分子构型的新方法

目前,用R/S法确定手性中心化合物的构型时,可以通过三度空间的透视图或费雪投影图,当然也可以用纽曼投影图。但是,不论用哪一种都需要有一定的空间概念。我们这里介绍一种新的、快速、简便的方法,即“±1,2,5规则”。采用这种方法,即使没有建立起空间概念的人,也可以确定含有手性中心化合物的R/S构型。由于费雪投影式是研究立体化学时广泛应用的表达式,因此在下面的讨论中,都采用费雪投影式。该方法的要点如下: 1.将手性中心(即手性碳原子)所连的四个原子或基团,按原子或基团数由大到小的次序用阿拉伯数字1,2,3,4进行编号;     

手性7-氨基脱氢松香酸乙酯的合成及表征

以脱氢松香酸为起始原料,通过酯化、氧化、手性辅剂亚胺化、还原以及酸解脱除手性辅剂等反应获得光学纯的 7 -（S）- 氨基脱氢松香酸乙酯 6a 和 7 -（R）- 氨基脱氢松香酸乙酯 6b。产物结构通过 1H NMR、13C NMR、MS 和 HRMS 进行表征,绝对构型经 X-ray 单晶衍射确定。     

对映体R/S构型的手指表示法

立体化学中具有手性C~*原子化合物的R/S构型,是通过三维空间的表示方法即透视法表示的。这种式子直观、容易确定原子团按由大到小的顺序的旋转方向,但书写麻烦,尤其对于结构复杂的化合物,在无模型时更难确定其构型。所以常采用E.Fischer     

金属卟啉在手性识别中的应用

从结构上分析了金属卟啉作为手性分子识别受体的优点,阐述了判断化合物绝对构型的激子手性方法机理,按照单卟啉体系和多卟啉体系介绍了金属卟啉与手性客体分子的识别机理和相关研究成果。初步系统化地对金属卟啉在手性识别中的应用进行综述,意为在相关领域工作的研究者提供参考。     

Stereoelective polymerization of β-butyrolactone

Racemic β-butyrolactone was polymerized using chiral initiators obtained from the reaction of organometallic derivatives (ZnEt₂, CdMe₂, AlEt₃) with R(−) 3,3 dimethyl-1,2 butanediol. With the zinc initiator, R(+) enantiomer is preferentially incorporated in the polymer chain with a stereoelectivity ratio r_R equal to 1.6. Crude polymer was fractionated into a crystalline, predominantly isotactic, part and an amorphous heterotactic part, both optically active. Sites of different stereospecificities, present in the initiator, are all active for the stereoelective polymerization. With the cadmium initiator, S(−) enantiomer is preferentially polymerized (r_s = 1.01), extending homosteric-antisteric rules previously established for thiiranes. Aluminium initiator leads to an homosteric process (r_R = 1.1). Chiroptical properties (o.r.d. and c.d.) of polymers prepared with zinc initiator show a predominance of R-configurational units, indicating that ring-opening occurs by O-acyl cleavage with retention of configuration.     

HPCE法手性拆分(R)-和(S)-3-羟基戊二酸乙酯

以β-环糊精(β-CD)为手性选择剂,采用毛细管区带电泳(CZE)对(R)-和(S)-3-羟基戊二酸乙酯进行手性拆分。通过考察手性选择剂浓度、电泳缓冲液pH、柱温以及分离电压对分离的影响,建立了比较理想的毛细管电泳手性拆分方法。在30 mmol/Lβ-CD、pH 5.0、柱温25℃以及分离电压20 kV分离条件下,(R)-和(S)-3-羟基戊二酸乙酯得到了完全分离。该分离方法具有较好的重复性和稳定性。     

Enantiocomplementary enzymatic resolution of the chiral auxiliary: cis,cis-6-(2,2-dimethylpropanamido)spiro[4.4]nonan-1-ol and the molecular basis for the high enantioselectivity of subtilisin Carlsberg

cis,cis-(+/-)-6-(2,2-Dimethylpropanamido)spiro[4.4]nonan-1-ol, 1, a chiral auxiliary for Diels-Alder additions, was resolved by enzyme-catalyzed hydrolysis of the corresponding butyrate and acrylate esters. Subtilisin Carlsberg protease and bovine cholesterol esterase both showed high enantioselectivity in this process, but favored opposite enantiomers. Subtilisin Carlsberg favored esters of (1S,5S,6S)-1, while bovine cholesterol esterase favored esters of (1R,5R,6R)-1, consistent with the approximately mirror-image arrangement of the active sites of subtilisins and lipases/esterases. A gram-scale resolution of 1-acrylate with subtilisin Carlsberg yielded (1S,5S,6S)-1 (1.1 g, 46 % yield, 99 % ee) and (1R,5R,6R)-1-acrylate (1.3 g, 44 % yield, 99 % ee) although the reaction was slow. The high enantioselectivity combined with the conformational rigidity of the substrate made this an ideal example to identify the molecular basis of the enantioselectivity of subtilisin Carlsberg toward secondary alcohols. When modeled, the favored (1S,5S,6S) enantiomer adopted a catalytically productive conformation with two longer-than-expected hydrogen bonds, consistent with the slow reaction rate. The unfavored (1R,5R,6R) enantiomer encountered severe steric interactions with catalytically essential residues in the model. It either distorted the catalytic histidine position or encountered severe steric strain with Asn155, an oxyanion-stabilizing residue.     

具有特定官能团化合物的手性传感研究进展

手性化合物在生命活动中起着重要作用,在医药学领域备受关注,建立快速高效的手性分析方法刻不容缓.手性传感方法具有专属性强、灵敏性高、操作简便、样品用量少等优点,能够快速确定对映体的绝对构型及对映体过量值.氨基、羟基和羧基是手性化合物中常出现的基团,也是手性传感器研究的重要对象.聚焦于纳米粒、量子点类手性传感材料和可用于手...     

手性氨基烷基酚的合成及其绝对构型的确定

合成了新型催化剂（1S，2R）-1-[[（1R）-1-（2-羟基-5-甲基苯基）乙基]氨基}-2-茚满醇，其结构通过IR、1H NMR和元素分析得到证实。绝对构型通过对其单晶的x-射线衍射结果分析，确定了新化合物的绝对构型为（S，R，R）。     

Chemoenzymatic synthesis of chiral carboxylic acids via nitriles

BACKGROUND: Enantiomerically pure 1,4‐benzodioxane‐2‐carboxylic acid derivatives are useful building blocks for the synthesis of pharmaceuticals and biologically active compounds whose interaction with their biological target (enzyme, receptor) depends very much on the absolute configuration of the chiral carbon at the 2‐position. The aim of the present work is to investigate the route to racemic nitriles and the subsequent selective enzymatic hydrolysis by nitrilase to optically active 1,4‐benzodioxane‐2‐carboxylic acid and 6‐formyl‐1,4‐benzodioxane‐2‐carboxylic acid. RESULTS: A range of microbial nitrilases from Rhodococcus, Alcaligenes and Pseudomonas strains have been prepared and screened for the desired biotransformations using a chiral high performance liquid chromatography (HPLC) analytical method. The nitrilase from Alcaligenes faecalis ATCC 8750 showed the highest and the nitrilase from Rhodococcus rhodochrous NCIMB 11216 the lowest activity towards 2‐cyano‐6‐formyl‐1,4‐benzodioxane. Lyophilised cells of Rhodococcus R 312 gave the (R)‐1,4‐benzodioxane‐2‐carboxylic acid with high enantioselectivity after 25% conversion. Excellent enantioselectivities for the hydrolysis of both 2‐cyano‐1,4‐benzodioxane as well as 2‐cyano‐6‐formyl‐1,4‐benzodioxane have been achieved and the absolute configuration of 1,4‐benzodioxane‐2‐carboxylic acid was determined to be R by comparison with the specific rotation of commercially available (R)‐1,4‐benzodioxane‐2‐carboxylic acid. CONCLUSIONS: This new nitrilase‐catalysed kinetic resolution of 2‐cyano‐ and 2‐cyano‐6‐formyl‐1,4‐benzodioxane opens a mild route to optically active 1,4‐benzodioxane‐2‐carboxylic acids. As the formyl functional group would be damaged in chemical nitrile hydrolysis, nitrilase‐catalysed hydrolysis solves this synthetic bottleneck and advances nitrilase biocatalytic tools for the preparation of more complex 1,4‐benzodioxane‐2‐carboxylic acids. Copyright © 2007 Society of Chemical Industry     

Preparation and characterization of novel optically active polyurethanes containing 1,1′‐binaphthol

Novel optically active polyurethanes (BPUs) based on chiral 1,1′‐binaphthol were synthesized via direct hydrogen transfer addition polymerization. The polymers were analyzed by FTIR, ¹H NMR, DSC‐TGA, CD spectra.The results showed that the specific rotation [α]²⁵_D were ?78.0° and +54.6° for the S‐BPU and R‐BPU respectively, and these polymers showed better thermal stability. The circular dichroism spectra of the chiral polymers were almost identical except that they gave opposite signals at each wavelength, and the infrared emissivity values of the S‐BPU and R‐BPU were 0.618 and 0.682, they displayed low infrared emissivity. Meantime the polymers implanted with PEG group exhibit better solubility, however thermal stability reduced to some extent. Some properties of the new optically active polyurethanes were reported. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

An Exploration of Induced Supramolecular Chirality Through Association of Chiral Ammonium Ions and Tartrates with the Achiral Host Cucurbit[7]uril

The chiral amines (R,R and S,S)-1-amino-2-benzyloxycyclopentane and (R and S)-α-methylbenzylamine were converted to ammonium (D and L) hydrogen tartrate salts and induced chiroptic effects were investigated following encapsulation in Q[7]. Significant chiroptic differences were observed in ORD and CD spectra for the two amines. The optical spectra were performed as a precursor study to a potential method for enantiomer separation, utilising Q[7] encapsulation in conjunction with enantio-pure hydrogen tartrates. An enantiomeric excess was achieved for the two antipodes of 1-amino-2-benzyoxycyclopentane but not for those of α-methylbenzylamine. However, material differences of crystallinity or the formation of a glass were observed for the latter amine induced by the different antipodes of hydrogen tartrate. ¹H NMR spectra of aminobenzyloxycyclopentane showed back-folding of the two rings with complete encapsulation in Q[7], leading to a secondary helical structure observed in CD spectra.