C-O Ring Construction: Ramariolide B (Sieber), (-)-Hedycoropyran A (Tong), (+)-Colomitide A (Jiao/Xie), (+)-Laurencin (West), (+)-Laurencin (Widenhoefer/Hong), Chivosazole F (Paterson)
Stephan A. Sieber of the Technische Universität München assembled (Chem. Commun. 2017, 53, 107. DOI: 10.1039/C6CC08365J) the spirocyclic lactone ramariolide B (2), isolated from the coral mushroom Ramaria cystidiflora, by stereoselective reduction of 1 followed by acid-catalyzed rearrangement of the resulting alcohol. He observed that synthetic 2 inhibited Mycobacterium tuberculosis (25 μM).
Hedycoropyran A (6) was isolated from the Asian herb Hedychium coronarium. Rongbiao Tong of the Hong Kong University of Science and Technology prepared (J. Org. Chem. 2017, 82, 1127. DOI: 10.1021/acs.joc.6b02738) 6 by the diastereoselective Heck coupling of 4 with 3, leading to 5.
Colomitide A (9), isolated from an aquatic fungus YMF 1.2076, showed significant animicrobial activity. En route to 9, Xiaozhen Jiao and Ping Xie of the Institute of Materia Medica, Beijing cyclized (Org. Biomol. Chem. 2017, 15, 3728. DOI: 10.1039/C7OB00539C) the triol 7 to the spirocycle 8.
Laurencin (12) was the first medium-ring ether isolated from Laurencia. F. G. West of the University of Alberta established (Org. Lett. 2017, 19, 552. DOI: 10.1021/acs.orglett.6b03719) the oxocene core of 12 by Stevens rearrangement to 11 of the ylide derived from 10.
In a complementary approach, Ross A. Widenhoefer and Jiyong Hong of Duke University prepared (Chem. Eur. J. 2017, 23, 7180. DOI: 10.1002/chem.201700499) the oxocene 14 by gold-catalyzed cyclization of 13 to 14. Both methods appear to be robust for medium-ring ether synthesis.
Chivosazole F (16), isolated from the myxobacterium Sorangium cellulosum, shows potent antiproliferative activity toward cancer cell lines, apparently by binding to G-actin. Ian Paterson of the University of Cambridge completed (Angew. Chem. Int. Ed. 2017, 56, 645. DOI: 10.1002/anie.201610636) the synthesis of 17 by stereoselective conversion of the aldehyde 15 to the (Z)-alkenyl iodide, followed by Stille coupling and deprotection. Remarkably, the carefully-assembled geometry of the polyenes of 15 was not affected by the Pd catalysis.