Kazunobu Kira

Mechanistic studies on the hydrosilylation of an acetylene cobalt complex; trapping an active catalyst Co2(CO)6 causing olefin-isomerization and O-silylation

Abstract We have recently reported a hydrosilylation reaction of acetylene cobalt complexes to produce the corresponding vinylsilanes. It has become clear that olefin-isomerization and O-silylation occurred under some hydrosilylation conditions. To avoid these side reactions, we found that hydrosilylation should be carried out in the presence of bis(trimethylsilyl)acetylene. The Co2(CO)6, which would cause side reactions, migrates to bis(trimethylsilyl)acetylene to form an acetylene cobalt complex. Mechanisms of olefin-isomerization and O-silylation are also discussed.

Synthesis of the BCDE rings of ciguatoxin 1B via an acetylene biscobalthexacarbonyl–vinylsilane strategy

Abstract A synthetic route to the BCDE rings of ciguatoxin 1B has been explored through acetylene biscobalthexacarbonyl complex and vinylsilane strategy. The key issues in the current synthesis are (i) ether ring cyclization by means of the acetylene cobalt complex and (ii) reductive decomplexation of the product endo -complexes into the corresponding vinylsilanes. A sequential cyclization route is also described along this line.

Synthesis of the BCD-ring of ciguatoxin 1B using an acetylene cobalt complex and vinylsilane strategy

Synthesis of the tricyclic BCD-ring segment with high stereoselectivity has been achieved starting from a sugar derivative directed toward the synthesis of the left part of ciguatoxin 1B. The central reactions in the synthesis are (i) ether ring formation mediated by an acetylene cobalt complex, (ii) decomplexation of the endo-acetylene cobalt complex to the vinylsilane, and (iii) ring-opening reaction of the epoxysilane into the allylic alcohol.

Acetylene cobalt complex and vinylsilane strategy in the synthesis of ciguatoxin (D)EF analog

Abstract A synthetic route to the (D)EF analog of ciguatoxin has been explored through acetylene cobalt complex and vinylsilane strategy. The central reactions in the synthesis are: (i) ether ring formation mediated by acetylene cobalt complex and (ii) decomplexation of the endo -acetylene cobalt complexes to vinylsilanes or olefins. Unusual rearrangement of epoxy-silane to allylic alcohol is also described.

Total Synthesis of 6-Deoxypladienolide D and Assessment of Splicing Inhibitory Activity in a Mutant SF3B1 Cancer Cell Line

A total synthesis of the natural product 6-deoxypladienolide D (1) has been achieved. Two noteworthy attributes of the synthesis are (1) a late-stage allylic oxidation which proceeds with full chemo-, regio-, and diastereoselectivity and (2) the development of a scalable and cost-effective synthetic route to support drug discovery efforts. 6-Deoxypladienolide D (1) demonstrates potent growth inhibition in a mutant SF3B1 cancer cell line, high binding affinity to the SF3b complex, and inhibition of pre-mRNA splicing.

Abstract 5564: Total synthesis of 6-deoxypladienolide D and assessment of splicing inhibitory activity in a mutant SF3B1 cancer cell line

Hotspot mutations in several components of the spliceosome have been reported in various hematological (CLL, MDS, etc.) and solid tumor (melanoma, pancreatic, etc.) malignancies. SF3B1 is a component of the U2 snRNP complex of the spliceosome and is involved in the recognition of 3′-splice sites during early spliceosomal assembly. We and others have demonstrated that mutations in SF3B1 result in neomorphic activity and trigger the production of aberrantly spliced transcripts. Thus, the discovery of small molecule modulators of SF3B1 splicing activity may have therapeutic potential in cancers harboring SF3B1 mutations. Members of the pladienolide family of natural products have been shown to affect RNA splicing through interaction with SF3B1. We have found that one particular natural product in this family, 6-deoxypladienolide D, demonstrates potent growth inhibition and cellular lethality in Panc 05.04 cells (a hotspot mutant SF3B1 cancer cell line). Due to the limited natural supply of 6-deoxypladienolide D and our interest in identifying chemical matter able to modulate splicing in these newly-identified mutant SF3B1 cancers, a total synthesis of 6-deoxypladienolide D using versatile and modular fragments was initiated. We will describe the first total synthesis of the natural product 6-deoxypladienolide D. Two noteworthy synthetic attributes are: 1) a late-stage allylic oxidation which proceeds with full chemo-, regio-, and diastereoselectivity and 2) the use of cost-effective starting materials and reagents to enable access to 6-deoxypladienolide D and its analogs for biological evaluation. We will show that 6-deoxypladienolide D demonstrates: 1) high binding affinity to the SF3b complex, 2) ability to modulate canonical pre-mRNA splicing, and 3) modulation of aberrant splicing induced by mutant SF3B1. Citation Format: Kenzo Arai, Silvia Buonamici, Betty Chan, Laura Corson, Atsushi Endo, Baudouin Gerard, Ming-Hong Hao, Craig Karr, Kazunobu Kira, Linda Lee, Xiang Liu, Jason T. Lowe, Tuoping Luo, Lisa A. Marcaurelle, Yoshiharu Mizui, Marta Nevalainen, Morgan Welzel O9Shea, Eun Sun Park, Samantha A. Perino, Sudeep Prajapati, Mingde Shan, Peter G. Smith, Parcharee Tivitmahaisoon, John Yuan Wang, Markus Warmuth, Kuo-Ming Wu, Lihua Yu, Huiming Zhang, Guo Zhu Zheng, Gregg F. Keaney. Total synthesis of 6-deoxypladienolide D and assessment of splicing inhibitory activity in a mutant SF3B1 cancer cell line. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5564. doi:10.1158/1538-7445.AM2015-5564