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Published online: 12th December, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)58
Mechanistic Insight into Catalytic Aerobic Chemoselective α-Oxidation of Acylpyrazoles

Seiya Taninokuchi, Ryo Yazaki,* and Takashi Ohshima*

*Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan

Abstract

Mechanistic studies on catalytic aerobic chemoselective α-oxidation of acylpyrazoles, including control experiments, kinetic isotope effect experiments, and radical clock experiments, are described. The key to promoting the reaction was the in-situ generation of a copper(II) peroxo complex, which serves as a Lewis acid/Brønsted base cooperative catalyst for efficient enolization. The present catalysis was applicable to late-stage α-oxidation of functionalized acylpyrazoles. A preliminary diastereoselective reaction using readily available chiral acylpyrazoles demonstrated that the present catalysis provided access to optically active α-hydroxy acid derivatives.

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Published online: 12th December, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)14
Exploration of Moderate Conditions and Substrate Variation in the Direct Condensation between Phthalide and Primary Amine Catalyzed by GaCl3. Are Aliphatic Amines Less Reactive than Aromatic Ones?

Ichiro Takahashi,* Yoshinori Nishiwaki, Kenta Saitoh, Takatoshi Matsunaga, Akihiro Aratake, Toshio Morita, and Shinzo Hosoi

*Department of Applied Chemistry and Biotechnology, Faculty of Engineering, University of Fukui, 9-1 Bunkyo 3-chome, Fukui-shi, 910-8507, Japan

Abstract

Direct condensation between phthalide and a primary amine in the presence of Lewis acid was achieved for the first time in organic solvent-diluted reaction systems catalyzed by GaCl3. The peripheral aspects of this reaction is discussed.

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Published online: 12th December, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)73
Asymmetric Synthesis of 2,3-Dimethoxy-8-oxoberbine, Precursor of O-Methylbharatamine

Maria Chrzanowska,* Agnieszka Dreas, and Zofia Meissner

*Faculty of Chemistry, Adam Mickiewicz University, Umultowska 89b, 61-614 Poznań, Poland

Abstract

The enantiospecific and enantioselective syntheses of 2,3-dimethoxy-8-oxoberbine were performed using the lateral metallation methodology. In the enantiospecific synthesis (4S)-2,2,4-trimethyl-3-(o-toluoyl)oxazolidine incorporating (S)-alaninol as the chiral auxiliary was applied. The addition reaction of benzylic anion generated in situ from chiral oxazolidine into 6,7-dimethoxy-3,4-dihydroisoquinoline led to the protoberberine with high enantiomeric excess. Enantioselective synthesis of 2,3-dimethoxy-8-oxoberbine was performed with achiral 2,2-dimethyl-3-(o-toluoyl)oxazolidine in the presence of chiral ligands. Among them (–)-sparteine and (+)-sparteine surrogate turned out to be the most efficient ones.

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Published online: 11th December, 2018

Short Paper | Regular issue | Prepress
DOI: 10.3987/COM-18-14001
Three New Chromone Derivatives from Cassia pumila and Their Anti-Tobacco Mosaic Virus Activity

Guang-Hui Kong, Yu-Ping Wu, Yin-Ke Li, Jing Li, Wei-Song Kong, Xin Liu, Yong Xu, Guang-Yu Yang, Qiu-Fen Hu,* and Wan-Li Zeng*

*Key Laboratory of Chemistry in Ethnic Medicinal Resources, State Ethnic Affairs Commission & Ministry of Education, Yunnan Minzu University, Kunming 650031, China

Abstract

Three new (1-3), together with four known chromone derivatives (4-7), were isolated from Cassia pumila. Their structures were elucidated by spectroscopic methods, including extensive 1D- and 2D NMR techniques. Compounds 1-3 were evaluated for their anti-tobacco mosaic virus (Anti-TMV) activity. The results showed that compounds 1-3 showed potential anti-TMV activities with inhibition rates of 28.3%, 31.2%, and 34.8%, at the concentration of 20 µM, respectively. These rates are close to that of positive control.

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Published online: 10th December, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)68
β-Trichloroacetylation of Cyclic Amines: Application to Synthesis of Chiral Azabicyclo-N-oxyls

Masami Kuriyama, Satoshi Kamogawa, Kosuke Yamamoto, and Osamu Onomura*

*Graduate School of Biomedical Sciences, Nagasaki University, Bunkyo-machi, Nagasaki 852-8521, Japan

Abstract

β-Trichloroacetylation of cyclic amines was developed under mild reaction conditions, and the desired trichloroacetylated products were obtained in good yields. This method was applied to the preparation of optically active azabicyclo compounds, which were converted to chiral azabicyclo-N-oxyls.

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Published online: 7th December, 2018

Short Paper | Regular issue | Prepress
DOI: 10.3987/COM-18-13978
Facile and Solvent-Free Synthesis of Quinazolin-4(3H)-ones under Microwave Condition Promoted by SbCL3

Jun Li, Weili Wang,* Xinglin Su, Xiaoling Zhang, Yan Zhang, Xuewen Zhang, Mengmeng Cai, Yuqian Cao, Juan Jin, and Yanbin Xu*

*School of chemistry and material science, Ludong University, No. 186 Hongqi Middle Road, Zhifu District, 264025, China

Abstract

Antimony trichloride (SbCl3) was found to be an effective catalyst (1 mol%) for one-pot synthesis of quinazolin-4(3H)-ones in good to excellent yields using anthranilamide and acyl chlorides under microwave irradiation. This method has the advantages of simplicity, mild reaction conditions, highly tolerant to several functional groups, as well as the avoidance of hazardous solvents.

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Published online: 7th December, 2018

Short Paper | Regular issue | Prepress
DOI: 10.3987/COM-18-14003
Three New Limonoids from the Fruits of Melia toosendan

Qiong Zhang,* Min Li, Qing-Hong Zheng, and Zhi-Da Min

*Department of Pharmaceutical Science, Shanxi Medical University, 56 Xinjian South Road, Taiyuan, Shanxi Province 030001, China

Abstract

Three new limonoids, 12-ethoxynimbolinins I-K (1-3), were isolated from the fruits of Melia toosendan. Their structures were established on the basis of spectroscopic methods. In addition, Compounds 1-3 were evaluated for their antibacterial activities.

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Published online: 7th December, 2018

Paper | Regular issue | Prepress
DOI: 10.3987/COM-18-14014
Brevisulcenal-G, -H, and –I, Polycyclic Ether Marine Toxins from the Dinoflagellate Karenia brevisulcata

Masayuki Satake,* Raku Irie, Yuka Hamamoto, Kazuo Tachibana, Patrick T. Holland, D. Tim Harwood, Feng Shi, Veronica Beuzenberg, Yoshiyuki Itoh, Fumiaki Hayashi, and Huiping Zhang

*Department of Chemistry, Graduate School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan

Abstract

Members of two classes of marine polycyclic ether compounds, brevisulcenals (KBTs) and brevisulcatic acids (BSXs), were isolated as causative toxins from a red tide (Karenia brevisulcata) bloom event in New Zealand in 1998. The new analogues, brevisulcenals (KBTs)-G, -H, and -I, were isolated from neutral lipophilic extracts of bulk dinoflagellate culture extracts, and the molecular structures of these compounds were elucidated by detailed analyses of NMR and matrix-assisted laser desorption/ionization tandem mass spectrometry spectra, and by comparison with the spectra of KBT-F. All the analogues have the same size and arrangement of 24 ether rings, but differ in their backbone substitution patterns and degree of terminal oxidation. The cytotoxicity of these new KBT analogues was greater than that of the co-isolated, KBT-F.

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Published online: 5th December, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)56
Synthetic Studies on Pyrroloindolizidine Skeleton Based on Gold–Catalyzed Hydroamination–Enamine Cyclization–Ring–Closing Metathesis Strategy

Kenji Sugimoto,* Natsumi Matsuo, Daisuke Tominaga, and Yuji Matsuya*

*Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, 2630 Sugitani, Toyama 930-0194, Japan

Abstract

A pyrroloindolizidine skeleton, which is observed in myrmicarin alkaloids isolated from African ant, is highly unique, oligocyclic indolizidine derivative. We describe here an attempt on a synthesis of a pyrroloindolizidine skeleton with our originally developed gold–catalyzed cascade reaction and a newly developed synthetic route for the skeleton via gold–catalyzed hydroamination–enamine cyclization–ring–closing metathesis.

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Published online: 5th December, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)59
Rapid Stereoselective Syntheses of Heteroarene-Fused Azacycles via Diastereoselective Conjugate Addition of Heteroaryl Substituted Lithium Amides

Stephen G. Davies,* Ai M. Fletcher, Katherine E. Holder, Paul M. Roberts, James E. Thomson, and David Zimmer

*Department of Chemistry, Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford, OX1 3TA, U.K.

Abstract

Conjugate addition of heteroaryl substituted lithium amides to a range of α,β-unsaturated esters followed by in situ enolate oxidation with (–)-(camphorsulfonyl)oxaziridine gave the corresponding α-hydroxy-β-amino esters. Subsequent Friedel-Crafts type cyclisation of these α-hydroxy-β-amino esters gave a range of heteroarene-fused azacycles in good yields and high diastereoselectivities.

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Published online: 3rd December, 2018

Short Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)76
Divergent Synthesis of Photoaffinity Probe Candidates by Click Reactions of Azido-Substituted Aryltrifluoromethyldiazirines

Kenji Watanabe, Junpei Tsuda, Hidenori Ochiai, Takashi Niwa, and Takamitsu Hosoya*

*Laboratory of Chemical Bioscience, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University (TMDU), 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan

Abstract

Two types of azido-substituted aryltrifluoromethyldiazirine units have been designed and prepared for the divergent synthesis of photoaffinity probe (PAP) candidates. Using these azides, various aryltrifluoromethyldiazirine derivatives have been rendered easily synthesizable by several click reactions, as well as the Staudinger reduction affording the corresponding aniline. The triazole-conjugated aryltrifluoromethyldiazirine derivatives prepared in this study showed normal photoreactivity compared with those reported previously. These results indicate the utility of these azido-substituted aryltrifluoromethyldiazirine units for development of PAPs for target identification of bioactive compounds.

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Published online: 30th November, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)72
Synthesis of Diverse 3-Azido-5-(azidomethyl)benzene Derivatives via Formal C–H Azidation and Functional Group-Selective Transformations

Yoshitake Nishiyama, Yoshihiro Misawa, Yuki Hazama, Kazuhiro Oya, Suguru Yoshida,* and Takamitsu Hosoya*

*Laboratory of Chemical Bioscience, Institute of Biomaterials and Bioengineering, Tokyo Medical and Dental University (TMDU), 2-3-10 Kanda-Surugadai, Chiyoda-ku, Tokyo 101-0062, Japan

Abstract

3-Azido-5-(azidomethyl)benzene derivatives are useful compounds for preparing diverse bistriazole compounds and photoaffinity probes for target identification of bioactive compounds. To more easily synthesize a diverse range of diazido compounds, a facile method for synthesizing diazido compounds bearing a transformable functional group, such as iodo, bromo, methoxycarbonyl, or cyano group, was developed. This method is based on formal C–H azidation of 1,3-disubstituted benzenes via regioselective borylation followed by deborylative azidation, with subsequent transformations, such as that of a one-carbon unit on the benzene ring to an azidomethyl group. The functional groups of the diazido compounds were efficiently transformed to various connecting groups, including carboxy, (succinimidyloxy)carbonyl, hydroxymethyl, formyl, bromomethyl, tosylthiomethyl, ethynyl, diazoacetyl, bromoacetyl, boryl, hydroxy, aminocarbonyl, amino, and isothiocyanato groups, leaving the azido groups untouched. Several diazido building blocks were used to prepare diazido compounds by forming amide, thiourea, and sulfide bonds via conjugation at the connecting groups. These results show that the method described here would facilitate diazido probe syntheses and bistriazole library construction.

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Published online: 29th November, 2018

Short Paper | Regular issue | Prepress
DOI: 10.3987/COM-18-13993
Synthesis of Imidazolium Salts Bearing Two Cyclodextrins

Susumu Tsuda,* Yohei Minami, Ryoji Ueda, Takanori Iwasaki, Shin-ichi Fujiwara, Hitoshi Kuniyasu, and Nobuaki Kambe*

*Depertment of Chemistry, Faculty of Dentistry, Osaka Dental University, 8-1 Kuzuhahanazono-cho, Hirakata, Osaka 573-1121, Japan

Abstract

Cyclodextrin (CD) homo and hetero dimers including an imidazolium salt were prepared from imidazolyl CDs and the corresponding CD monotosylates. The CD dimer imidazolium salts were characterized by MALDI-TOF mass and NMR spectroscopies.

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Published online: 28th November, 2018

Communication | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)50
Acetal Elimination Reaction Accompanied with Regioselective Ring Opening of 1,4-Bisacetal-1,4-epoxy-1,4-dihydronaphthalenes

Yoshinari Sawama,* Takahiro Kawajiri, Yuta Yamamoto, Yuko Shishido, Ryota Goto, and Hironao Sajiki*

*Laboratory of Organic Chemistry, Gifu Pharmaceutical University 1-25-4 Daigaku-nishi, Gifu 501-1196, Japan

Abstract

1,4-Epoxy-1,4-dihydronaphthalenes are useful precursors to synthesize 1-naphthols by an acid-catalyzed ring opening of their 1,4-epoxy moieties. 1-Acetal-substituted 1,4-epoxy-1,4-dihydronaphthalene was also converted to 1-naphthol via the unique iron-catalyzed ring opening of the 1,4-epoxy moiety followed by the elimination of the acetal moiety. The present method could be applied to the regioselective syntheses of highly-functionalized 4-formyl-1-naphthols from the unsymmetrical 1,4-bisacetal-substituted 1,4-epoxy-1,4-dihydronaphthalenes.

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Published online: 28th November, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)85
Synthesis and Properties of a Tricyclic Hexaketone Monohydrate with Hexabutyl Side Chain

Mio Ishita, Masanori Ohkoshi, Yoshiyuki Kuwatani, Hiroyuki Otani, Tohru Nishinaga, and Masahiko Iyoda*

*Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, Hachioji, Tokyo 192-0397, Japan

Abstract

A tricyclic hexaketone monohydrate with a hemiacetal structure was synthesized by the ruthenium-catalyzed oxidation of butyl-substituted tribenzotetradehydro[12]annulene-1,2-dione. The oxidation of the annulenedione afforded unique [12]annulene-1,2,5,6,9,10-hexaone, followed by the cyclization to produce corresponding tricyclic hydrate containing two dihydrobenzopyranone rings. The tricyclic hexaketone hydrate weakly interacts with methanol and ethylene glycol to form 1:1 complexes in solution.

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Published online: 22nd November, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)65
The Practical Synthesis of Dissymmetrical 1,3,5-Trioxazatriquinane Derivatives Comprised of Three Distinct Carbonyl Compounds

Shigeto Hirayama, Koji Obayashi, Naohisa Wada, Kousuke Ohyama, Shizuho Fuku, Koji Koyano, Fumika Karaki, Kennosuke Itoh, Hiroshi Nagase, and Hideaki Fujii*

*Laboratory of Medicinal Chemistry, School of Pharmacy, Kitasato University, 5-9-1, Shirokane, Minato-ku, Tokyo 108-8641, Japan

Abstract

We have previously synthesized various 1,3,5-trioxazatriquinane derivatives consisting of not only three identical carbonyl compounds but also two identical carbonyl moieties as well as another type of carbonyl compound. However, dissymmetrical derivatives prepared from three distinct carbonyl compounds have not yet been selectively synthesized. Herein, we developed a selective synthetic method of such dissymmetrical derivatives: free α-hydroxyaldehydes were slowly added to a solution of protected α-hydroxyaldehydes, ammonium chloride, and sodium acetate to selectively provide key intermediate oxazolines, which were successfully converted into the objective dissymmetrical derivatives.

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Published online: 22nd November, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)43
[Bis(trifluoroacetoxy)iodo]p-nitrobenzene and [Bis(trifluoroacetoxy)iodo]pentafluorobenzene as Lead Reagents for the Direct Ring Contraction of Lactams to Pyrrolidines

Samuel Aubert-Nicol, Nora Heinrich, Jean Lessard, and Claude Spino*

*Chemistry Department, University of Sherbrooke, 2500 Boul. Université, Sherbrooke, QC, J1K 2R1, Canada

Abstract

Two λ3iodanes, namely [bis(trifluoroacetoxy)iodo]p-nitrobenzene and [bis(trifluoroacetoxy)iodo]pentafluorobenzene, were used to effect the direct ring-contraction of lactams to pyrrolidines. Intense reaction optimization was necessary but only α,α-disubstituted lactams succumbed to our efforts thus far.

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Published online: 22nd November, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)63
Enantioselective Synthesis of 2,4,5-Trisubstituted Tetrahydropyrans via Peptide-Catalyzed Michael Addition Followed by Kishi’s Reductive Cyclization

Atsushi Ueda,* Mei Higuchi, Tomohiro Umeno, and Masakazu Tanaka*

*Graduate School of Biomedical Sciences, Nagasaki University, 1-14 Bunkyo-machi, Nagasaki 852-8521, Japan

Abstract

An enantioselective synthesis of 2,4,5-trisubstituted tetrahydropyrans has been achieved in four steps from α,β-unsaturated ketones and dimethyl malonate by peptide-catalyzed asymmetric Michael addition and diastereoselective construction of tetrahydropyran rings by Kishi’s reductive cyclization as key steps. A variety of α,β-unsaturated ketones were converted to the 1,4-products with high enantioselectivities (83–98% ee).

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Published online: 21st November, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)42
A [3,3] Sigmatropic and Novel Ipso [3,3] Sigmatropic Rearrangement of 1-Hydroxyindole Chemistry

Yoshikazu Fukui, Tetsuya Kobayashi, Toshiya Kawasaki, Fumio Yamada, and Masanori Somei*

*Faculty of Pharmaceutical Sciences, Graduate School of Natural Science and Technology, Kanazawa University, Kakuma-machi, Kanazawa, 920-1192, Japan

Abstract

Utilizing 1-aryloxyindole derivatives, we found a new type of [3,3] sigmatropic rearrangement reaction. We named it as ipso [3,3] sigmatropic rearrangement. The product structures are strictly determined by X-ray crystallographic analysis. Normal [3,3] sigmatropic rearrangement of 1-hydroxyindole derivative was found to be a useful synthetic method for 2H-pyrazino[1',2':1,5]pyrrolo[2,3-b]indole-1,4-dione derivative.

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Published online: 20th November, 2018

Review | Special issue | Prepress
DOI: 10.3987/REV-18-SR(F)3
Renovation of Glycomolecules for Molecular Imaging Studies: Low-Affinity Glycan Ligands can be Used for Selective Cell Imaging?

Shogo Nomura and Katsunori Tanaka*

*Biofunctional Synthetic Chemistry Laboratory, Cluster for Pioneering Research, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan

Abstract

Since the interaction of single molecule of glycans is very weak to the lectins, in most cases they have been formed into clusters for binding studies. Then, a glycan molecule cannot be used for efficient cell imaging or targeting? We established a new strategy to selectively image the cells by using synergistic interaction of peptide and glycan ligands on cell surface. Namely, the peptide ligand with high affinity to the target surface receptor was pretargeted, and then the low-affinity glycan ligand with fluorescent label was interacted to the same cell; Bioorthogonal reaction between them can anchor the label on the target cells when both receptors are expressed and close in space on the surface. When the lectin is not expressed on the target or two receptors are separated, the weakly interacting glycan ligands are washed away the cells, hence the target cells are selectively imaged. While new idea and proof-of-concept data were exemplified based on our previous research, using this strategy, we would like to report the new data to visualize cell surface dynamics in response to the treatment with bioactive compounds.

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Published online: 20th November, 2018

Short Paper | Regular issue | Prepress
DOI: 10.3987/COM-18-13955
Synhesis, Molecular Docking Studies and in vitro Antimicrobial Evaluation of Novel Pyrimido[1,2-a]quinoxaline and Triazino[4,3-a]quinoxaline Derivatives

Rania B. Bakr,* Nadia A. A. Elkanzi , Amira A. Ghoneim, and Shaima M. N. Moustafa

*Department of Pharmaceutical Organic Chemistry, Faculty of Pharmacy, Beni-Suef University, Beni-Suef 62514, Egypt

Abstract

A series of 3-substituted-2,6-dihydro-1H-pyrimido[1,2-a]quinoxaline- 5-carboxylates (4a,b), (8c,d) and (13a,b) were prepared by treating ethyl 3-amino-1,4-dihydroquinoxaline-2-carboxylate (1) with alkylidenemalononitrile derivatives. Moreover, 8H-benzo[5,6][1,2,4]triazino[4,3-a]quinoxaline-7-carboxylate derivatives (18, 20, 22, 24) were synthesized from condensation reaction between diazonium salts 16 with resorcinol, 1-naphthol, malononitrile and ethyl acetoacetate respectively. Some of the newly synthesized compounds were screened for their antimicrobial activity studies. Furthermore, molecular docking were performed on the active compounds 1, 4a and 8c to predict the mode of action of these novel compounds.

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Published online: 20th November, 2018

Short Paper | Regular issue | Prepress
DOI: 10.3987/COM-18-13990
An Efficient Synthesis and Evaluation of Antitumor Activities of Functionalized Pyrano[2,3-b]quinolines

Wei Lin, Mengye Zhang, Ning Wang, Wentao Xu, and Daqing Shi*

*Key Laboratory of Organic Synthesis of Jiangsu Province, College of Chemistry, Chemical Engineering and Materials Science, Soochow University, Suzhou 215123, Jiangsu, China

Abstract

An efficient synthesis of novel functionalized pyrano[2,3-b]quinoline derivatives via a three-component reaction of 2-chloroquinoline-3-carbaldehydes, malononitrile and 1,3-dicarbonyl compounds under microwave irradiation is described. This protocol has the advantages of high efficiency, mild reaction conditions, a one-pot procedure, and convenient operation. All of these compounds were evaluated for their antiproliferative properties in vitro against hepatic carcinoma cells and several compounds were found to have good activities.

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Published online: 19th November, 2018

Communication | Regular issue | Prepress
DOI: 10.3987/COM-18-13988
New Facile Synthesis of 3-Substituted 7,8-Dihydroquinolin-5(6H)-ones and [1]Benzopyrano[4,3-b]pyridin-5-ones Using 2-(Hetero)arylvinamidinium Salts

Yiyi Weng, Chen Sun, Qingwei Cao, Hantao Chen, Nanhui Li, Zhuo Chen, and Weike Su*

*Collaborative Innovation Center of Yangtze River Delta Region Green of Pharmaceuticals, Zhejiang University of Technology, Hangzhou 310014, China

Abstract

The method of cyclocondensation of 3-amino-2-cyclohexen-1-ones 2 or 4-aminocoumarin 3 with symmetrical 2-(hetero)aryl-vinamidinium salts 1 has been developed, providing an efficient synthetic pathway to access novel functionalized 3-substituted 7,8-dihydroquinolin-5(6H)-ones 4 or [1]benzopyrano[4,3-b]pyridin-5-ones 5 in good to excellent yields. All the aryl-substituted and heterocyclic-substituted vinamidinium salts undergo a facile electrocyclic ring closure to form pyridine ring with α,β-unsaturated ketones. A possible mechanism for the formation of pyridine ring is proposed.

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Published online: 16th November, 2018

Short Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)54
Bimetallic Lewis Acid Template-Mediated Enantioselective Hetero-Diels-Alder Reactions of 4-Siloxy-2,4-pentadienols

Jun Ishihara,* Yuka Ohzono, Kengo Oka, Yasuhiro Urayama, and Susumi Hatakeyama

*Graduate School of Biomedical Sciences, Nagasaki University, Nagasaki, 852-8521, Japan

Abstract

Enantioselective hetero-Diels-Alder reactions catalyzed by a bimetallic Lewis acid template are described. The hetero-Diels-Alder reactions of 4-siloxy-2,4-pentadienols and various dienophiles by the chiral H8-BINOL template provide a general entry into the substituted dihydropyrans with good enantioselectivities. This protocol is also applicable to a dihydropirazine formation.

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Published online: 15th November, 2018

Paper | Regular issue | Prepress
DOI: 10.3987/COM-18-13969
Synthesis, Characterization and Antimicrobial Evaluation of Some Novel Fused Pyrimido[1,2-b][1,2,4]triazine, Triazino[2,3-a]quinazoline and Imidazo[1,2-b][1,2,4]triazine Derivatives

Khaled S. Mohamed* and Elsherbiny H. El-Sayed

*Engineering Chemistry Department, Higher Institute for Engineering and Technology, New Damietta, Egypt

Abstract

A novel pyrimido[1,2-b][1,2,4]triazine derivatives were synthesized by allowing 3-amino-1,2,4-triazine (1) to react with different reagents such as enaminone, enaminonitriles, 3-bromopropanenitile, 2-(2,5-dimethoxybenzylidene)malononitrile and 1,3-dicarbonyl compounds. Moreover, triazino[2,3-a]quinazoline derivatives were synthesized by reaction of 1 with 2-((dimethylamino)methylene)-5,5-dimethylcyclohexane-1,3-dione (18) and 2,6-bis(pyridin-3-ylmethylene)cyclohexan-1-one (20). On the other hand, treatment of 1 with 2-bromo-1-(naphtho[2,1-b]furan-2-yl)ethan-1-one (22) afforded imidazo[1,2-b][1,2,4]triazine derivative (23). The newly synthesized compounds were evaluated for their antimicrobial activities based on inhibition diameter zone against Gram positive and Gram negative bacteria.

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Published online: 15th November, 2018

Short Paper | Regular issue | Prepress
DOI: 10.3987/COM-18-13991
A Pair of New Non-glycosidic Iridoid Epimers from Scrophularia ningpoensis

Wei Zhang, Peng Liu, Xin-Yu Ji, Xiang-Yang Chen, Yan-Yan Jiang, and Bin Liu*

*School of Chinese Materia Medica, Beijing University of Chinese Medicine, Beijing 102488, China

Abstract

A pair of new non-glycosidic iridoid epimers, ningpogenins A and B (1a/1b), together with eighteen known ones (2-19) were isolated from the roots of Scrophularia ningpoensis. Their structures were elucidated by spectroscopic analyses, including 1D-, 2D-NMR, and HR-ESI-MS. Compound 1 is an unusual example of natural ningpogenin—L-pyroglutamic adducts. In addition, the cytotoxic effects of the new compound against HepG2, U251 and SH-SY5Y cell lines were evaluated.

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Published online: 14th November, 2018

Communication | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)48
One-Step Synthesis of 4H-3,1-Benzoxazin-4-ones from Weinreb Amides and 1,4,2-Dioxazol-5-ones via Cobalt-Catalyzed C–H Bond Activation

Iku Tanimoto, Kentaro Kawai, Akane Sato, Tatsuhiko Yoshino,* and Shigeki Matsunaga*

*Faculty of Pharmaceutical Sciences, Hokkaido University, Kiat12, Nishi 6, Kita-ku, Sapporo, Hokkaido, 060-0812, Japan

Abstract

A one-step synthesis of 4H-3,1-benzoxazin-4-ones from readily available Weinreb amides and 1,4,2-dioxazol-5-ones under Cp*Co(III) catalysis is described. The reactions proceeded in moderate to good yields with high functional group compatibility.

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Published online: 14th November, 2018

Short Paper | Regular issue | Prepress
DOI: 10.3987/COM-18-13981
New Prenylated Bibenzyls from Bornean Liverwort Acrobolbus saccatus

Shean-Yeaw Ng, Takashi Kamada, Chin-Soon Phan, Monica Suleiman, and Charles S. Vairappan*

*Laboratory of Natural Products Chemistry, Institute for Tropical Biology and Conservation, Universiti Malaysia Sabah, 88400 Kota Kinabalu, Sabah, Malaysia

Abstract

Liverworts are the most primitive terrestrial plant which known to produce unique and wide variety of compounds. Ethyl acetate crude extract was subjected to several chromatographic techniques for purification. Three new compounds, saccatenes A-C (1-3) were isolated together with two known prenyl bibenzyl derivative, 2,2-dimethyl-5-hydroxy-6-carboxy-7-(2-phenylethyl) chromene (4) and radulanin A-5-one (5) from the Bornean liverwort Acrobolbus saccatus (Hook.) Trevis collected from Mountain Trus Madi, Sabah, Malaysia. The structures of the three new metabolites were established by analyses of the spectroscopic data (1D NMR, 2D NMR, HRESIMS and IR), and the antibacterial activity against eight selected human pathogenic species of bacteria were tested.

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Published online: 14th November, 2018

Paper | Regular issue | Prepress
DOI: 10.3987/COM-18-13984
Utilization of Chlobenthiazone and Benazolin-ethyl as 4-Substituted 2(3H)-Benzothiazol-2-one Scaffolds

Masatoshi Kakuno, Shotaro Izawa, Taichi Takemoto, and Yoo Tanabe*

*Department of Chemistry, School of Scienece and Technology, Kwansei Gakuin University, Sanda, Hyogo 669-1337, Japan

Abstract

N(3)-Substituted 4-aryl (or heteroaryl)-2(3H)-benzothiazol-2-ones were synthesized from readily accessible chlobenthiazone and benazolin-ethyl, a couple of N(3)-substituted 4-chloro-2(3H)-benzothiazol-2-one pesticides, utilizing Suzuki-Miyaura cross-coupling reactions (9 examples; 44–98% yield), although with less reactive stereocongested 4-chloro pendant substituent. In a similar fashion, N(3)-substituted 4-anilino (or BocNH)-2(3H)-benzothiazol-2-ones were synthesized from the 4-bromo analogues of the chlobenthiazone-utilizing Buchwald-Hartwig cross-coupling reactions (3 examples; 50–89% yield). In addition, a short synthesis of the key chloro-type quinone segment in natural mevashuntin with a unique 2(3H)-benzothiazol-2-one skeleton, was performed in three short steps with 61% overall yield. The obtained quinone segment functioned as a Diels-Alder reaction dienophile toward the Danishefsky-Kitahara diene as the model experiment. All schemes utilized a common cyclo-condensation using chlorocarbonylsulfenyl chloride for the construction of 4(ortho)-substituted 2(3H)-benzothiazol-2-one substrates.

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Published online: 12th November, 2018

Paper | Special issue | Prepress
DOI: 10.3987/COM-18-S(F)78
Consice Synthesis of TAN1251C

Yosuke Nagasaka, Tomohiro Asakawa, Sayaka Shintaku, Akitaka Masuda, Kosuke Matsumura, Makoto Inai, Yoshinobu Ishikawa, Masahiro Egi, Yoshitaka Hamashima, and Toshiyuki Kan*

*School of Pharmaceutical Sciences, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka-shi, 422-8526, Japan

Abstract

An efficient total synthesis of TAN1251C was accomplished by employing Ugi four-component condensation reaction and Dieckmann condensation to construct the spiro-fused cyclohexanone and γ-lactam ring structure. Diastereoselective reduction by side-chain-controlled hydrogenation of enamide 37 or Zn reduction of oxime 48 enabled construction of the amino group with the desired stereochemistry.

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