Studies on the synthesis of the "northern" and "southern" segments of boromycin and aplasmomycin

Graduation date: 1984The stereocontrolled synthesis of the southern lactone 17 of\ud boromycin and of the northern segments of both boromycin and aplasmomycin\ud are described. The syntheses begin with enantioselective\ud epoxidation of 3-buten-2-ol (42) to provide the optically active\ud 2(S),3(R) epoxy alcohol 43. The absolute configuration was confirmed\ud by preparing 43 from (-)-2,3-dihydroxybutyric acid (45). 2,5-Dide-\ud __\ud oxyribonofuranose (54) and 2,5-dideoxyribono-y-lactone (55) were\ud synthesized from 43.\ud Segments 61 and 39, corresponding to the southeast quadrant of\ud boromycin, and 100 and 107, representing northwest quadrants of\ud aplasmomycin and boromycin, were also prepared from 43. The northeast\ud and southwest quadrants of boromycin and aplasmomycin, 74, were synthesized\ud in optically active form from isobutyraldehyde. Coupling\ud of 74 with 61, followed by modification of functionalities, provided\ud the southern lactone 17 of boromycin. In an intramolecular oxyselenation\ud study for the formation of the tetrahydrofuran ring in the\ud northern segments of boromycin and aplasmomycin, treatment of cis\ud olefinic sulfone 96 with phenylselenyl chloride provided predominantly\ud the 2,5-cis isomer, whereas the trans olefinic sulfone 106 gave the\ud desired 2,5-trans isomer as a major product.\ud The acyl dithiane 129 was prepared from 83, but coupling of this\ud compound with carboimide 131 failed, presumably due to the weak nucleophilicity\ud of the anion of the dithiane. The more reactive 1,3-\ud dithiane 137 was prepared from 124 for the purpose of adding C(1) and\ud C(2) to aplasmomycin