C-O Ring Construction: Tanikolide (Yakura), Siladenoserinol (Doi), Hongkonoid D (Yue), Catunaregin (Abe/Ito), Chromodorolide B (Overman), Biselyngbyolide B (Goswami/Maier)
Takayuki Yakura of the University of Toyama observed high diastereoselectivity in the rearrangement of the diazo ketone 1 to the ester 2. This established the oxygenated cyclic quaternary center of tanikolide (3) (Tetrahedron 2018, 74, 1059. DOI: 10.1016/j.tet.2018.01.035).
The extract of a tunicate of the family Didemnidae collected in Indonesia showed inhibitory activity against the p53-Hdm2 interaction. Siladenoserinol A (6) was a major contributor to that activity. A key step in the synthesis of 6 developed by Takayuki Doi of Tohoku University was the Au-catalyzed cyclization of 4 to 5 (Angew. Chem. Int. Ed. 2018, 57, 5147. DOI: 10.1002/anie.201801659).
Jian-Min Yue of the Shanghai Institute of Materia Medica achieved substantial diastereoselectivity in the Claisen rearrangement of 7. On deprotection the product readily cyclized to 8, that was carried on to hongkonoid D (9) (J. Am. Chem. Soc. 2018, 140, 2485. DOI: 10.1021/jacs.7b10135).
Hideki Abe and Hisanaka Ito of the Tokyo University of Pharmacy and Life Sciences found that methanesulfonic acid was particularly effective for the cyclization of 10 to 11. Deprotection completed the synthesis of catunaregin (12) (Eur. J. Org. Chem. 2018, 1655. DOI: 10.1002/ejoc.201800219).
The chromodorolides, represented by chromodorolide B (16), resemble natural products that are known to have significant effects on the Golgi apparatus. En route to 16, Larry E. Overman of the University of California, Irvine developed the radical cascade coupling of 13 with 14 (J. Am. Chem. Soc. 2018, 140, 3091. DOI: 10.1021/jacs.7b13799).
Rajib Kumar Goswami of the Indian Association for the Cultivation of Science assembled the cytotoxic macrolide biselyngbyolide B (19) by the intramolecular Heck cyclization of 17 to 18 (Org. Lett. 2016, 18, 1908. DOI: 10.1021/acs.orglett.6b00713). Martin E. Maier of the Eberhard Karls Universität Tübingen reported an improved preparation of 17 (J. Org. Chem. 2018, 83, 4554. DOI: 10.1021/acs.joc.8b00298).