HETEROCYCLES

■ Contents

■ Survey of Briarane-Type Diterpenoids – Part VII

Yu-Hsin Chen, Hsien-Kuo Chin, Bo-Rong Peng, You-Ying Chen, Chiung-Chin Hu, Li-Guo Zheng, Thanh-Hao Huynh, Tung-Pin Su, Yi-Lin Zhang, Zhi-Hong Wen, Tsong-Long Hwang,* Yang-Chang Wu,* and Ping-Jyun Sung*

*National Museum of Marine Biology and Aquarium, Pingtung 94450, Taiwan

Abstract

The structures, names, bioactivities, and references of 78 briarane-type natural products, including 56 new metabolites, isolated between 2017 and 2019 are summarized in this review article. All the briarane diterpenoids mentioned in this review were isolated from the octocorals Alcyonacea belonging to genus Briareum; the Gorgonacea belonging to genus Junceella and Subergorgia; and the Pennatulacea belonging to genus Anthoptilum. Some of these compounds exhibited potentially biomedical activities, including anti- inflammatory activity, antiviral activity, and cytotoxicity.

■ Sulfamic Acid-Catalyzed Conversion of o-Aminothiophenol and Aromatic Aldehydes to 2-Arylbenzothiazoles

Xiaofeng Yu,* Renyuan Song, Chunjie Shi, and Guangrong Wang

*School of Materials and Chemical Engineering, Bengbu University, Bengbu, Anhui 233030, P. R. China

Abstract

Non-metallic, non-toxic, and cheap sulfamic acid was used as a catalyst for the synthesis of 2-arylbenzothiazole from o-aminothiophenol and aromatic aldehydes bearing electron-donating or electron-withdrawing groups. The sulfamic acid catalyst can be reused without any change in catalytic effect. The drug GW610 was successfully synthesized on a hundred-gram scale using this synthetic route.

■ Convenient Synthesis of 2,3-Dihydro-1,2,4-thiadiazoles, 4,5-Dihydro-1,3-thiazoles, and 1,3-Thiazoles through a [4+1]-Type Oxidative Ring Closure of 1,3-Thiaza-1,3-butadienes

Kazuaki Shimada,* Megumi Isogami, Kitami Maeda, Rei Nishinomiya, and Toshinobu Korenaga

*Department of Chemistry and Biosciences, Faculty of Science and Engineering, Iwate University, Morioka, Iwate 020-8551, Japan

Abstract

1,3-Thiaza-1,3-butadienes bearing an N,N-dimethylamino group at the C-2 position were efficiently converted into 5H-1,2,4-oxathiazoles, 2,3-dihydro-1,2,4-thiadiazoles, 4,5-dihydro-1,3-thiazoles, and 1,3-thiazoles through an oxidative ring closure by treating with mCPBA, chloramine-T, metal carbenoids, or dichlorocarbene, respectively, via the ring closure of in situ generated heterocumulene-type reactive species involving thione S-oxides, thione S-imides, and thiocarbonyl ylides.

■ Facile and Convenient Synthesis of New Isoxazolo[5,4-b]pyridine, Pyrrolo[3,2-d]isoxazole, Isoxazolo[5,4-b]azepine-4,7-dione and Isoxazole Derivatives with Potential Anticancer Activity

Ahmed El-Mekabaty* and Mona E. Ibrahim

*Chemistry Department, Faculty of Science, Mansoura University, El-Gomhoria Street, ET-35516 Mansoura, Egypt

Abstract

The readily available 3-methylisoxazol-5-amine (1) has been used as a key intermediate for the synthesis of isoxazolo[5,4-b]pyridine, pyrrolo[3,2-d]isoxazole, isoxazolo[5,4-b]azepine-4,7-dione and isoxazole derivatives via its reactions with some chemical reagents. Sixteen compounds were designed to study their cytotoxic properties against three human cell lines: colorectal carcinoma (HCT-116), prostate cancer (PC3) and normal lung fibroblast (WI-38), using the MTT colorimetric assay. 5-Fluorouracil, a well-known anticancer drug, was used for comparison. Among the tested candidates, pyrrolo[3,2-d]isoxazole 5 and isoxazole derivatives 11-14 showed the highest activity against the tested cancer cell lines with good selectivity by their lower toxicity against normal cells.

■ Highly Regioselective Synthesis of 1-Acyl-5-hydroxypyrazolines or Synthesis of 3,5-Disubstituted Pyrazoles from (E)-β-Chlorovinyl Ketones and Benzohydrazides or Hydrazine Hydrate

Haotian Wu, Rongrong Hou, Ye Yuan, Jingli Zhang,* Bifeng Chen, and Taolei Sun*

*School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, 122 Luoshi Road,Wuhan,Hubei 430070, China

Abstract

Highly regioselective synthesis of 1-acyl-5-hydroxypyrazolines or synthesis of 3,5-disubstituted pyrazoles have been achieved through the cyclocondensation of (E)-β-chlorovinyl ketones with benzohydrazides/hydrazine hydrate under extremely mild reaction conditions. The mechanistic studies showed that diverse electrophilic pathways of (E)-β-chlorovinyl ketones could be observed by using different nucelophilic species. Moreover, the utility of the tandem reaction is further illustrated by the concise synthesis of 1-acyl-pyrazole and 3-pentyl-5-phenyl-1H-pyrazole.

■ Ruthenium(II)-Catalyzed Regioselective C-H Hydroxymethylation of N-Aryl-azaindoles with Paraformaldehyde

Siqi Li, Yang Yu,* Yaxi Yang, and Bing Zhou*

*Department of Medicinal Chemistry, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, 555 Zu Chong Zhi Road, Shanghai 201203, PR, China

Abstract

A facile synthesis of hydroxymethylated N-aryl-azaindoles was developed via a Ru(II)-catalyzed regioselective C-H addition to paraformaldehyde. The reaction is compatible with air, shows high functional group tolerance and regioselectivity, and is an environmentally benign method without any undesired byproduct.

■ Facile Synthesis of 2-Aryl(guaiazulen-1-yl)methylkojic Acid Derivatives via Benzylation

Xin-Shuang Xiong, Dao-Lin Wang,* Si-Tong Guo, and Xiao-Liang Zhang

*College of Chemistry and Chemical Engineering, Bohai University, 19, Keji Rd., New Songshan District, Jinzhou City, Liaoning Province 121001, China

Abstract

A facile and efficient one-pot procedure for the preparation of 2-aryl(guaiazulen-1-yl)methylkojic acid derivatives by a catalyst-free, benzylation of guaiazulene with kojic acid-substituted benzylic alcohols under mild conditions in good yield is reported.

■ Convenient Methods for the Synthesis of Novel Thiadiazoles and Polythiadiazoles

Abedlwahed R. Sayed* and Yasair S. Al-Faiyz

*Department of Chemistry, Faculty of Science, King Faisal University, Hofuf 31982, Saudi Arabia

Abstract

In this study, the novel thiadiazoles were formed via the reaction of hydrazonoyl halides with methyl 2-(adamantan-2-ylidene)hydrazinecarbodithioate. Also, the reaction of 2,5-dihydrazinyl-1,3,4-thiadiazoles with 2-adamantanone or acetylferrocene produced the 2,5-bis(2-(adamantan-2-ylidene)hydrazinyl)-1,3,4-thiadiazole or 2,5-bis(2-(1-(ferrocenylidene)hydrazinyl)-1,3,4-thiadiazole, respectively. Analogously, treatment of terephthalaldehyde with 2,5-dihydrazinyl-1,3,4-thiadiazole afforded new poly(benzylidenehydrazinyl-1,3,4-thiadiazole). Finally, the reaction of bishydrazonoyl halides with 2,5-dihydrazinyl-1,3,4-thiadiazole afforded new poly(1,3,4-thiadiazolo[2,3-c][1,2,4]triazine). The synthetic structures for the final products are suggested and discussed. The compound structures of the products were recognized by different spectroscopic analyses.