Synthesis of the tricyclic core of alkaloid securinol B using a cascade of Vilsmeier-Haack and Mannich cyclizations

Iminium ions generated upon amide activation were trapped sequentially with tethered nucleophiles. This cascade of cyclizations constitutes a new synthetic strategy that was applied to the construction of the tricyclic core of alkaloid securinol B.     

Enantioselective Synthesis of Glutarimide Alkaloids Cordiarimides A,B, Crotonimides A,B, and Julocrotine

Five glutarimide alkaloids cordiarimide A ( 5 ), cordiarimide B ( 6 ), crotonimide A ( 3 ), crotonimide B ( 4 ), and julocrotine ( 2 ) have been synthesized starting from Boc‐L‐glutamine ( 7 ). The benzylic alcohol chiral centre of cordiarimides B ( 6 ) has been established in 6:1 diastereoselectivity by catalytic asymmetric hydrogenation using Zhou's catalytic system Pd(CF₃CO₂)₂/(R,R)‐Me‐DuPhos.     

A flexible and unified strategy for syntheses of cladospolides A, B, C, and iso-cladospolide B

A simple, efficient and flexible strategy for the syntheses of cladospolides A-C and iso-cladospolide B is reported here. This strategy involves Julia-Kocienski olefination and Yamaguchi macrolactonization as key steps, starting from either d-ribose or suitable tartaric acid esters. Although our initial efforts towards cladospolide A involving a ring closing metathetic approach were not successful, changing the mode of ring closure and the use of Julia-Kocienski olefination for the construction of the key intermediate solved this issue and paved the way for the completion of total syntheses of this class of natural products.     

Total synthesis and stereochemical confirmation of manassantin A, B, and B1

Stereocontrolled total syntheses of manassantins A, B, and B1 and saucerneol are described for the first time based on a novel cycloetherification of end-differentiated benzylic alcohols as a common intermediate. [structure: see text].     

Concise, asymmetric, stereocontrolled total synthesis of stephacidins A, B and notoamide B

Concise asymmetric total syntheses of the fungal metabolites (-)-stephacidin A, (+)-stephacidin B, and (+)-notoamide B are described. Key features of these total syntheses include (1) a facile synthesis of (R)-allyl proline methyl ester, (2) a revised route toward the pyranoindole ring system, (3) a novel cross-metathesis strategy for the introduction of important functional groups, and (4) an SN2' cyclization to form the [2.2.2] bridged bicyclic ring system. Furthermore, our synthesis has taken advantage of microwave heating to shorten reaction times as well as increase yields for the preparation of vital intermediates.     

Synthesis of slagenins A, B, and C

[structure: see text] A short synthesis of the marine sponge metabolites slagenins A (1), B (2), and C (3) is described. The synthetic route features the preparation of beta-hydroxyimidazolone 4 from ornithine and its subsequent oxidative cyclization to the slagenin core.     

Structures of neopolyoxins A,B, and C

The absolute structures of fungal chitin synthetase inhibitors, neopolyoxins A, B, and C were determined as 1, 2, and 3 respectively on the basis of chemical and spectroscopic evidence.     

Photoactive liquid crystalline polymers: A comprehensive study of linear and hyperbranched polymers synthesized by A2B2, A2B3, A3B2, and A3B3 approaches

A series of linear and hyperbranched polyester epoxies, with varied structural parameters such as kinked structure and different dendritic architectures, were synthesized by A₂ + B₂, A₂ + B₃, A₃ + B₂, and A₃ + B₃ approaches. The structures of synthesized monomers and polymers were confirmed by Fourier transform infrared, ¹H NMR, and ¹³C NMR spectroscopic techniques. The effect of varied structural parameters on phase behavior and photoresponsive properties was investigated by using differential scanning calorimeter, thermal optical polarized microscope, UV–visible spectroscopy, photoviscosity, and refractive index studies. The transition temperatures of hyperbranched polymers were higher than that of the corresponding linear analogues. All the polymers showed nematic phase (nematic droplets) over a broad temperature range. The effect of kinked structural unit on photoresponsive property is less in both linear and hyperbranched architectures. Although the effect of architectural nature is highly considerable within the hyperbranched architectures, the polymer (HPE–33) synthesized by A₃ + B₃ approach showed highest rate of photocrosslinking, followed by HPE–I 32; HPE–T 32, and HPE–23, which were synthesized by A₃ + B₂ and A₂ + B₃ approaches, respectively. The findings in photoresponsive properties were further supported by molecular modeling studies. Substantial variation of refractive index (0.015–0.024) indicates that these polymers could be used for optical recording. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Stereochemistry of pteriatoxins A, B, and C

The C34 and C2' stereochemistry of pteriatoxins A-C has been established. The availability of all the stereoisomers via total synthesis has played an indispensable role.     

五味子素A、B和五味子丙素的密度泛函研究

采用密度泛函B3LYP方法在6-31G基组水平上对五味子素A、B及五味子丙素3种五味子提取物进行了优化计算,并从平衡几何构型、前线分子轨道、净电荷分布等方面对计算结果做了比较.计算结果表明分子中的二氧五环对分子的药物活性具有较大影响.随着分子中二氧五环数目的增加,分子中联苯环扭转角减小,前线轨道能级和能级差都减小,联苯环上正电荷增加,由此可判断3种分子活性顺序应为五味子丙素>五味子素B>五味子素A.     

Collective Synthesis of Schilancidilactones A,B and Schilancitrilactones A,B, C, 20‐epi‐Schilancitrilactone A

Schisandraceae triterpenoids are novel natural products that contain highly fused ring systems bearing multiple chiral centers surrounding. Some of them exhibit promising bioactivities, such as antitumor, anti‐HIV, etc. In this article, we describe our efforts to the collective total synthesis of schilancidilactones A, B, schilancitrilactones A, B, C, and 20‐epi‐schilancitrilactone A from common precursors. An intramolecular radical cyclization, late‐stage halogenation and AIBN‐mediated or Ni‐catalyzed intermolecular radical cross coupling reaction were employed as the key steps.     

First enantioselective total synthesis of penicimarin B,aspergillumarins A and B

A convergent enantioselective synthesis of penicimarin B, aspergillumarin A and B has been reported using Brown’s allylation, DeBrabander–Bhattacharjee lactonization and Grubbs cross coupling metathesis. During this synthesis we have standardized the conditions for DeBrabande–Bhattacharjee lactonization to obtain excellent yield (>90%).     

Solid-phase synthesis of cyclic hexapeptides wollamides A,B and desotamide B

Solid-phase synthesis of antibacterial cyclohexapeptides including wollamides A, B and desotamide B has been developed. Briefly, the protected linear hexapeptides were assembled on 2-chlorotrityl chloride resin using standard Fmoc chemistry and diisopropylcarbodiimide/hydroxybenzotriazole coupling reagents, cleaved off-resin with hexafluoroisopropanol/dichloromethane to keep side-chain protecting groups intact, and cyclized in solution. Final global removal of all protecting groups using a cocktail of trifluoroacetic acid/triisopropylsilane/dichloromethane afforded the desired cyclic hexapeptides, which were characterized by ¹H, ¹³C NMR, and HRMS. Subsequent investigation of macrocyclization parameters such as terminal residues, coupling reagents, and cyclization concentration revealed the optimized conditions for the synthesis of this class of cyclic hexapeptides.     

Bioinspired synthesis of hirsutellones A, B, and C

The total synthesis of hirsutellones A (1), B (2), and C (3) has been achieved through a bioinspired late-stage sequence starting from advanced intermediate 6. The sequence proceeded via labile intermediate 17,1'-dehydrohirsutellone B (5) and delivered, in addition to the natural products (1-3), hirsutellone analogue 1',2',17-epi-hirsutellone C (1',2',17-epi-3).     

Total syntheses of furaquinocin A, B, and E

A modular approach to the total synthesis of furaquinocins culminated in the total syntheses of furaquinocin A, B, and E. A Pd-catalyzed dynamic kinetic asymmetric transformation (DYKAT) on carbonates derived from Baylis-Hillman adducts, followed by a reductive Heck cyclization allows the enantio- and diastereoselective construction of dihydrobenzofuran 32. Introduction of a double unsatured side chain via Horner-Wadsworth-Emmons reaction and assembly of the naphthoquinone with squaric acid based methodology leads to furaquinocin E. The use of differentially substituted squaric acid derivatives allows the synthesis of three analogues of furaquinocin E. The additional stereocenters in furaquinocin A and B can be introduced with a diastereoselective Sakurai allylation. The stereoselective elongation of the side chain is possible using cross metathesis or ring closing metathesis. The obtained late-stage intermediates were successfully transformed to furaquinocin A and B.     

Concerning Venturicidin B, Botrycidin and the sugar components of Venturicidins A and B

The known antibiotic Venturicidin A and two new antifungal compounds, Venturicidin B and Botrycidin, have been isolated from a strain of Streptomyces aureofaciens DUGGAR . Venturicidin B gave on methanolysis the methyl glycoside of 2-deoxy-D -rhamnose, Venturicidin A the corresponding 3-O-carbamate.     

Structure and stability of B6, B,and B clusters

We investigated various isomers of B₆, B, and B clusters with ab initio [Hartree–Fock (HF), MP2)] and density functional theory (DFT) methods. Ten B₆ isomers, 6 B isomers, and 6 B isomers are determined to be local minima on their potential energy hypersurfaces by the HF, B3LYP, B3PW91, and MP2 methods. Fourteen of these structures are first reported. The most stable neutral B₆ cluster is the capped pentagonal pyramid (C_5v), in agreement with the results reported previously. Hexagon B (C_2h) isomer and fan‐shaped B (C_2v) isomer are found to be the most stable on the cationic and anionic energy hypersurfaces, respectively. Natural bond orbital analysis suggests that there are three‐centered bonds in the most stable B₆ neutral and ionic clusters. The multicentered bonds are responsible for the special stability of the lowest‐energy isomer. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem 94: 269–278, 2003     

Stereoselective synthesis of musclides A1, A2 and B

An expedient method for the stereoselective preparation of musclide A1, A2 and B, cardiotonic-potentiating principles from musk, has been achieved. The key step is the addition of the O-benzyl ethers of prop-2-yn-1-ol and (R)-but-3-yn-2-ol to aldehydes mediated by zinc triflate, Et₃N, and (+)- or (−)-N-methylephedrine. In some cases, the partial reduction of the resulting alkynols to Z-olefins has allowed us to remove the minor stereoisomer easily by chromatography to afford highly stereoenriched precursors of musclides.     

五脂酮A, B和Butyryl Binankadsurin A的分离与结构

从采自广西柳州地区融水县的一种南五味子(Kadsurasp.)种子中分得三个已知化合物---binankadsurinA(1),acetylbinankadsurinA(2),angeloylbinankadsurinA(3)及三个新化合物---五脂酮(schisanlignone)A(4),B(5),butyrylbinankadsurinA(6)。它们的结构由光谱分析和化学转化而阐明。1系首次从自然界分得。在抗癌药理筛选中,4与5在体外都对白血病P-388细胞有抑制作用。其IC~5~0分别为10和40μg/mL。     

Total Synthesis of Neuroprotective Dictyoquinazol A,B, and C

A new protective compound, dictyoquinazol A, was synthesized starting from 5‐methoxy‐2‐nitrobenzoic acid in six‐steps in 36% overall yield. Two derivatives B and C, isolated from the mushroom Dictyophora indusiata, were also synthesized from Dictyoquinazole A.