Diels-Alder Cycloaddition: Kalihinol C (Shenvi), Lepadin B (Chen), Stachyflin (Magauer), Antrocin (Su/Yang), Wickerol A (Trauner), Morphine (Chen)
The isocyanoterpenes, represented by kalihinol C (4), show remarkable activity against Plasmodium falciparum. Ryan A. Shenvi of Scripps/La Jolla described a synthesis of 4 centered on the next chapter in his development of dendralene sequential Diels-Alder cycloadditions, assembling 3 by combining 1 with 2 (J. Am. Chem. Soc. 2017, 139, 3647. ).
The alkaloid (-)-lepadin B (8) is a potent blocker of certain nicotinic acetylcholine receptors. En route to 8, Xiaochuan Chen of Sichuan University observed remarkable diastereoselectivity in the Diels-Alder cycloaddition of 5 with 6 to give 7 (Org. Lett. 2017, 19, 5372. ).
The meroterpenoids, represented by (-)-stachyflin (12), show significant activity against methicillin-resistant Staphylococcus aureus. Thomas Magauer of the University of Innsbruck developed a general route to this class of natural products, preparing the key intermediate 11 by combining the chirons 9 and 10 (Nature Commun. 2017, 8, 2083. ).
(-)-Antrocin, isolated from a fungus that grows on the Niu-Zarng tree, shows activity against MDA-MB-231 breast cancer cells. In the course of a synthesis of (+)-antrocin (15), Ming-Der Su of the National Chiayi University and Te-Fang Yang of the National Chi Nan University achieved remarkable diastereoselectivity in the cyclization of the camphanate 13 to 14 (J. Org. Chem. 2017, 82, 9576. ).
Wickerol A (19), isolated from the fungus Trichoderma atroviride FK1-3849, shows potent activity against type A/H1N1 influenza virus. Dirk Trauner of the Ludwig-Maximilian University Munich found that the Diels-Alder cyclization of 16 with the sensitive diene 17 to give 18 was best promoted by the catalyst combination developed by Jung (J. Am. Chem. Soc. 2017, 139, 9491. ).
David Y.-K. Chen of Seoul National University oxidized the phenol 20 to a triene, that cyclized to 21. The alkene bridge of 21 was then oxidized, leading to the morphinans, including morphine (22) (Chem. Sci. 2017, 8, 7031. ).