Stereoselective synthesis of (R)-(+)-1-methoxyspirobrassinin, (2R,3R)-(−)-1-methoxyspirobrassinol methyl ether and their enantiomers or diastereoisomers

Stereoselective synthesis of cruciferous indole phytoalexin (R)-(+)-1-methoxyspirobrassinin and its unnatural (S)-(−)-enantiomer was achieved by spirocyclization of 1-methoxybrassinin in the presence of (+)- and (−)-menthol and subsequent oxidation of the obtained menthyl ethers. Methanolysis of menthyl ethers in the presence of TFA afforded (2R,3R)-(−)-1-methoxyspirobrassinol methyl ether as well its unnatural (2S,3S)-, (2R,3S)-, and (2S,3R)-isomers.     

Menthol

The biosynthesis of menthol comprises eight steps, starting from isopentenyl‐ and dimethylallyl diphosphate. On technical scale it is produced from cresol by the Haarmann‐Reimer‐process. The enantiomers are separated by crystallization. The Takasago‐Menthol‐process is one of the most famous enantioselective industrial processes. The key step is a rhodium‐catalyzed double‐bond migration. BASF's new menthol process, which is based on citral, includes an enantioselective hydrogenation.     

毛细管柱气相色谱法测定角膜接触镜护理液中薄荷脑

角膜接触镜护理液样品以乙酸乙酯超声提取,提取液经离心后供气相色谱测定。采用DB-Wax毛细管柱(30m×0.32mm,0.5μm)分离样品,氢火焰离子化检测器检测,内标法定量。薄荷脑线性范围为3.74～187.2mg.L-1,方法的检出限(3S/N)为0.15mg.L-1。方法用于护理液中薄荷脑的测定,回收率在98.3%～99.3%之间;相对标准偏差(n=6)在0.72%～1.95%之间。     

用GC-MS法分析春、秋季薄荷油成分

用毛细管气相色谱－质变法对同一种薄荷春季、秋季茎叶中挥发油的精细成分进行了分析测试,分离出春季薄荷油中20个组分、秋季薄荷油中16个组分,通过计算机库存质谱图和标准谱图册检索鉴定出各个组分对应的化合物,用峰面积归一化方法计算出各组分的相对含量,其中春季薄荷以（cis)－薄荷酮(3.70%）、（2R－cis）－薄荷酮（1.25%）、（1α,2α,5β）－薄荷醇（16.88％）、（1α,2β,5β）－薄荷醇(74.98%)为主,秋季薄荷以(cis)-薄荷酮(3.88%)、(2R-cis)-薄荷酮(1.24%)、（1α,2α,5β）－薄荷醇(15.76%)、（1α,2α,5β）－薄荷醇(69.97%)、α-蒎烯(2.68%)、β－蒎烯(2.07%)和拧檬烯(1.71%)为主。     

配合Pd催化剂薄荷醇与异丁烯羰基合成Validol

用PdCL2(PPh3)2/PPh3/P-CH3C6H4SO3H复合催化体系,在间歇高压釡中,以二甲苯为溶剂,在一定的反应温度、CO/H2压力和薄荷醇与异丁烯浓度下,研究了主催化剂浓度和各种助催化剂的配比对薄荷醇转化率和反应速度的影响.在适宜的催化体系和反应体系中,进行了反应物的转化率、Validol的选择性和收率与反应时间关系实验.对98%以上Validol产物进行了FT-TR、MS、13C NMR和1H NMR鉴别.最后,完成了反应温度、CO压力和薄荷醇、异丁烯浓度对羰基合成Validol反应速度的影响实验,提出了该反应的反应机理和催化循环过程.     

Release kinetics of (−)-menthol from chewing gum

The release kinetics of (−)-menthol from chewing gum was investigated using various encapsulated powder of (−)-menthol. The apparatus of flavor release of chewing gum was made with a glass container of mashing homogenizer. Flavor release behavior could be correlated with Avrami’s equation. Chewing gum containing (−)-menthol/γ-CD complex powder had longer retention of (−)-menthol compared with the β-CD complex powder and the (−)-menthol encapsulated in modified starches. The activation energies of (−)-menthol release from chewing gum were 106 kJ/mol for γ-CD complex and 74 kJ/mol for (−)-menthol/β-CD complex powder and emulsified (−)-menthol encapsulated in HI-CAP, respectively.     

Enantioselective room temperature phosphorescence detection of non-phosphorescent analytes based on interaction with beta-cyclodextrin/1-bromonaphthalene complexes

Menthol (MT) induces strong room temperature phosphorescence (RTP) of 1-bromonaphthalene (1BrN) in aqueous β-cyclodextrin (β-CD) suspensions, even under non-deoxygenated conditions. Interestingly, (−)-MT and (+)-MT enantiomers give rise to different phosphorescence intensities, the difference being 19 ± 3%. It is argued that the signal can be mainly ascribed to the formation of ternary complexes β-CD/1BrN/MT which show different RTP lifetimes, i.e. 4.28 ± 0.06 and 3.71 ± 0.06 ms for (−)-MT and (+)-MT, respectively. Most probably, the stereochemical structure of (−)-MT provides a better protection of 1BrN against quenching by oxygen than (+)-MT. This interpretation is in line with the observation that under deoxygenated conditions the phosphorescence intensity difference for the two complexes becomes very small, i.e. only about 4%.The lifetime difference under aerated conditions enables the direct determination of the MT stereochemistry. For mixtures, in view of the 0.06 ms uncertainty in the lifetime, enantiomeric purity can be determined down to 10%. Furthermore, in the case of MT the concentration of the least abundant enantiomer should be at least 3 × 10⁻⁴ M, since otherwise complex dissociation would obscure the lifetime difference.     

A stereoselective route to 6-substituted pyrrolo-1,5-benzoxazepinones and their analogues

We developed a novel and convenient stereoselective path for the preparation of pyrrolo-1,5-benzoxazepinones (PBOs). This innovative route envisaged the employment of (−)-menthol as convenient chiral auxiliary and a key S_NAr for the stereoselective preparation of a tertiary aryl–alkyl ether. As a further advancement, we exploited this newly conceived synthetic route for the preparation of 2-substituted PBO analogues to either undergo biological evaluation themselves or give access to a variety of further functionalization options.