Total synthesis of (±)-tangutorine and chiral HPLC separation of enantiomers

The first total synthesis of racemic tangutorine, a novel indole alkaloid, was performed in 7 steps. The key reactions, dithionite reduction and acidic cyclization provided easy access with good yields to the tangutorine skeleton. Comprehensive NMR spectroscopic data of new compounds are given. Chiral HPLC separation of enantiomers is reported.     

A new route to eremophilanes: synthesis of (±)-eremophilenolide, (±)-eremophiledinone, and (±)-deoxyeremopetasidione

A new and efficient route to the family of eremophilanes is reported. Key steps are the highly stereocontrolled Diels-Alder reaction and aldol condensation to furnish a cis-decalin system with the desired stereochemistry present in the eremophilane family of natural products. This approach is general and was utilized for the synthesis of (±)-eremophilenolide, (±)-eremophiledinone, and (±)-deoxyeremopetasidione.     

Fast analysis of nicotine related alkaloids in tobacco and cigarette smoke by megabore capillary gas chromatography

A novel fast megabore capillary gas chromatographic (MCGC) method for analysis of 7 nicotine related alkaloids in tobacco and cigarette smoke, including nicotine, nornicotine, myosmine, nicotyrine, anabasine, anatabine and 2,3-dipyridyl, was developed. The use of megabore capillary column GC methodology, equipped with flame ionization detector (FID), provided rapid, unambiguous nicotine related alkaloids analysis. One gram flue-cured tobacco (or Cambridge filter pad), 20 ml ether, and 5 ml 10% sodium hydroxide solution, added with n-heptadecane as the internal standard, were placed in a flask, and the flask was capped and placed in an ultrasonic bath for 15 min. A 1 microl volume was analyzed by capillary GC operating in split-injection mode on a mega bore Simplicity-5 column. This simple procedure was compared with the previously reported packed column GC method and the Griffith still-colorimetric method. The application of the method for analysis of various flue-cured tobaccos and cigarette smoke was discussed.     

Analyses of tobacco alkaloids by cation-selective exhaustive injection sweeping microemulsion electrokinetic chromatography

In this study, an on-line concentration method which coupled cation-selective exhaustive injection (CSEI) sweeping technology with microemulsion electrokinetic chromatography (MEEKC) was used to detect and analyze several tobacco alkaloids (nornicotine, anabasine, anatabine, nicotine, myosmine and cotinine) that are commonly found in various tobacco products. First, the effects of microemulsion compositions (oil, cosurfactant and solution pH) were examined in order to optimize the alkaloid separations in conventional MEEKC. The pH value and the injection length of basic plug were found to be the predominant influences on the alkaloid stacking. This optimal CSEI sweeping MEEKC method provided approximately 180- to 540-fold increase in detection sensitivity in terms of peak height without any loss in separation efficiency when compared to normal MEEKC separation. Furthermore, this proposed CSEI sweeping MEEKC method was applied successfully for the detection of the minor alkaloids nornicotine, anabasine and anatabine in tobacco products.     

全扫描-选择离子数据采集技术应用于烟草中生物碱的快速测定

建立了应用气相色谱-质谱(GC-MS)全扫描-选择离子监测(Scan-SIM)数据采集方式同时测定烟草中8种含量相差较大的生物碱的方法,采用Scan模式分析烟碱、降烟碱、新烟碱、去氢新烟碱,同时采用SIM模式分析麦斯明、二烯烟碱、2,3′-联吡啶、可铁宁。结果表明,烟草中各生物碱的回收率为94.8%～98.8%,5次测定的相对标准偏差均小于6%。该方法具有简单、快速、准确的特点,应用于烟草样品测定,结果令人满意。     

Formal synthesis of (±)-brazilin and total synthesis of (±)-brazilane

A convergent synthesis towards (±)-brazilin and (±)-brazilane has been reported from 3,4-dimethoxy benzaldehyde in <15 reaction steps. Palladium(II)-catalysed intramolecular Friedel–Crafts cyclisation and Lewis acid supported intermolecular Friedel–Crafts alkylation reactions have been demonstrated. A tetracyclic substituted indane common key intermediate is employed to furnish the desired two molecules in good to excellent yield. Pd(OH)₂ has played a crucial role in the total synthesis of (±)-brazilane.     

Total synthesis and structural confirmation of (±)-cuevaene A

The total synthesis and structural reassignment of cuevaene A have been completed. The key synthetic steps in the total synthesis included a base-promoted double conjugate addition and further elaboration to generate the tricyclic core structure, followed by construction of the trienoic acid side chain. Detailed comparison of proton and carbon NMR data with published values enabled the connectivity of the natural product, which had been debated in earlier publications, to be confirmed.     

Optimization study for the reversed-phase ion-pair liquid chromatographic determination of nicotine in commercial tobacco products.

The availability of published methods for the determination of nicotine in commercial tobacco products based on state-of-the-art chromatographic methods is limited. Nicotine is a diprotic base with pKa's of 3.12 (pyridine ring) and 8.02 (pyrrolidine ring). Other monoprotic and diprotic bases are also present in commercial tobacco including anatabine, nornicotine, anabasine, and cotinine. In this paper, the chromatography of nicotine and the minor tobacco alkaloids under reversed-phase ion-pairing conditions is thoroughly studied. The results of this study are used to understand the retention mechanisms of the tobacco alkaloids, to examine their observed elution order with respect to fundamental analyte properties (size, functionality, and acid-base strength), and to select optimum chromatographic conditions for the determination of nicotine in commercial tobacco products.     

First total syntheses of (±)-3-aza-11-selena and (±)-3-aza-11-tellura steroids

An efficient synthesis of 11-selena and 11-tellura steroids bearing a pyridine as an A ring was achieved via an intramolecular Diels-Alder cycloaddition of o-quinodimethanes, which were generated from a 3-azabicyclo[4.2.0]octa-1,3,5-trien-7-one ketal. The major isomer matches the trans-anti-trans ring configuration of natural products. Finally, the vinyl groups of the synthesized 11-hetero steroids have been oxidized by the Wacker process in good yields. The characteristic ¹H and ¹³C NMR spectroscopic features of the synthesized compounds are reported.     

Synthesis of (±)-coerulescine and a formal synthesis of (±)-horsfiline

A straightforward synthesis of (±)-coerulescine and (±)-horsfiline has been established from 3-formyl-3-phenylpyrrolidine employing 4-hydroxypiperidine as the starting material. There are two remarkable steps for the synthesis of (±)-coerulescine and (±)-horsfiline. One is the rapid access to produce 3-formyl-3-phenylpyrrolidine by Lewis acid-catalyzed rearrangement of 3,4-dihydroxy-4-phenylpiperidine. The other key step is an intramolecular electrophilic cyclization from 3-benzylcarbamoyl-3-phenylpyrrolidine to the 3,3-spirocyclic 2-oxindole ring skeleton.     

Concise syntheses of (±)-dichroanone, (±)-dichroanal B, (±)-taiwaniaquinol B, and (±)-taiwaniaquinone D

The total syntheses of dichroanone and dichroanal B, as well as the formal syntheses of taiwaniaquinol B and taiwaniaquinone D, are reported.     

Determination of tobacco alkaloids using solid phase microextraction and GC-NPD

Summary The sampling approaches using solid phase microextraction (SPME) were evaluated for the analysis of tobacco alkaloids. Because of their low volatility and ionic nature, sampling alkaloids from the headspace of dry or wet tobacco samples often required more effort to improve extraction efficiency. Directly dipping the SPME fiber coated with polydimethylsiloxane film into the tobacco extract was proved to be a simple, effective tool for sampling alkaloids from tobacco. When combined with the practice of fast GC and nitrogen-phosphorus detection, nicotine and a group of selected minor alkaloids (i.e., nornicotines, myosmine, anabasine and anatabine) were separated with baseline resolution within 3 min. The detection limits for these alkaloids are below 0.1 μg mL⁻¹. In addition, the carry-over problem frequently occurred in alkaloids analysis was eliminated. The influence of tobacco matrix and fiber aging on the partition of alkaloids, as well as the use of an internal standard to compensate these deviations, were also studied.     

Threo-(±)-开环异落叶松脂醇二阿魏酸酯的全合成

报道了双木脂素threo-(±)-开环异落叶松脂醇二阿魏酸酯的全合成. 以香草醛为原料, 经过两步Stobbe反应构建木脂素骨架, 然后再用LiAlH₄还原、加氢后, 产物经柱层析分离, 得到2个异构体meso-和threo-(±)-开环落叶松脂素; 根据其NMR, IR和HRMS等谱图确认发现, 极性较小的产物threo-(±)-开环落叶松脂素为合成的关键中间体. threo-(±)-开环落叶松脂素与甲氧甲基(MOM)保护的阿魏酸缩合得到目标产物threo-(±)-开环异落叶松脂醇二阿魏酸酯. 合成采用汇聚法, 经11步, 以约8%的总产率得到了目标产物. 该合成方法具有原料价廉易得及操作简便的优点, 并具有一定的实用价值.     

First total synthesis of (±)-puyanin and (±)- 4′-O-methylbonannione

A facile approach for the first total synthesis of two naturally occurring geranylated flavonoids, (±)-puyanin 1 and (±)-4′-O-methylbonannione 2 have been obtained with total yield 27% and 21%, respectively. The key steps were regioselective cyclization of geranylated tetrahydroxychalcone and regioselective geranylation of 2, 4, 6-trihydroxy- acetophenone.     

Total synthesis of (±)-antofine

An efficient preparation of (±)-antofine is described. The main steps involved in this synthesis are the Horner–Wadsworth–Emmons reaction, the intramolecular Schmidt reaction of an azido aldehyde, and the one-pot deprotection of the N-formyl group, followed by Pictet–Spengler cyclization. The asymmetric hydrogenation of the trisubstituted α,β-unsaturated ester is also explored, however only moderate enantio-control (55% ee) is obtained. Finally, (±)-antofine is prepared in six steps from the phenanthryl aldehyde 5 with an overall yield of 35%.     

The first total syntheses of (±)-Preussomerins K and L using 2-arylacetal anion technology

The first syntheses of newly isolated members of the Preussomerin family, Preussomerins K and L, are reported. Key steps include the functionalisation of a 2-arylacetal anion, one-pot Friedel-Crafts cyclisation-deprotection and reductive opening of epoxides.     

Protecting group free syntheses of (±)-columbianetin and (±)-angelmarin

A five-step and protecting group free synthesis of (±)-columbianetin from cyclohexane-1,3-dione is reported. The former compound was converted into its p-hydroxycinnamate derivative, (±)-angelmarin, using Coster’s esterification procedure. Efforts to modify the synthesis so as to prepare angelmarin and columbianetin in an enantioselective manner are described.     

The first total synthesis of (±)-zenkequinone B

The first total synthesis of tetrahydrobenzo[a]anthraquinone natural product (±)-zenkequinone B (1) is reported. The key step involves the TiCl₄-promoted intramolecular cyclization of 4-aryl-2-hydroxybutanal diethyl acetal 4 to give compound 3. The total synthesis of (±)-zenekequinone B (1) has been accomplished in five steps from readily available 2-(chloromethyl)-9,10-dimethoxyanthracene (5) in 40.3% overall yield.     

One-pot total syntheses of natural products containing a THP-ring backbone: (±)-centrolobine and (±)-civet cat secretion

A one-pot strategy is devised and applied to the total syntheses of natural products with a THP-ring backbone. A special feature of this one-pot synthesis is the recyclability of the indium complex byproduct generated from the indium-mediated allylation reaction for concurrent catalysis in subsequent steps. Centrolobine and civet cat secretion are synthesized via this new method in overall yields of 58% and 23%, respectively.     

Total syntheses of lindenane-type sesquiterpenoids: (±)-chloranthalactones A, B, F, (±)-9-hydroxy heterogorgiolide, and (±)-shizukanolide E

Chloranthalactones A, B, F, 9-hydroxy heterogorgiolide, and shizukanolide E are a family of natural lindenane-type sesquiterpenoids isolated mainly from chloranthaceae. A general synthetic strategy was accomplished by us for the racemic total syntheses of the five natural products. The key steps included substrate-controlled Matteson epoxidation of ketone and highly diastereoselective intramolecular Hodgson cyclopropanation to construct the challenging cis, trans-3/5/6 tricyclic skeleton, along with a methodology developed for the γ-alkylidenebutenolide ring formation.