Partially hydroxylated 2,5-disubstituted bis-tetrahydrofurans from carbohydrates

The diverse bioactivities of annonaceous acetogenins have recently attracted increasing interest. Many of these natural products contain one or more 2,5-disubstituted tetrahydrofuran rings as a core unit; these are important for the bioactivity, since it is believed that these anchor the compounds to the surface of the membrane. Therefore, the synthesis of functionalized bis-tetrahydrofurans is an important task and we have developed a synthetic pathway to all four diastereomeric, partially hydroxylated bis-tetrahydrofurans, that is, 3,6:7,10)-dianhydro-2,8,9-trideoxy-L-erythro-D-ido-undecitol (1), 3,6:7,10-dianhydro-2,8,9-trideoxy-D-threo-D-ido-undecitol (2), 3,6:7,10-dianhydro-2,8,9-trideoxy-L-threo-D-ido-undecitol (3), and 3,6:7,10-dianhydro-2,8,9-trideoxy-D-erythro-D-ido-undecitol (4) starting from D-glucose. The reaction of the aldose with Meldrum's acid led to the C-glycosidic 3,6-anhydro-1,4-lactone 6, which was converted to the aldehyde building block 2,5-anhydro-3,4,7-tri-O-benzyl-6-deoxy-aldehydo-D-ido-heptose (11). Chain elongation of 11 with the Grignard reagent derived from 1-bromo-3-butene gave the diastereomers 3,6-anhydro-1,4,5-tri-O-benzyl-2,8,9,10,11-pentadeoxy-L-glycero-D-ido-undec-10-enitol (12) and 3,6-anhydro-1,4,5-tri-O-benzyl-2,8,9,10,11-pentadeoxy-D-glycero-D-ido-undec-10-enitol (13). The relative threo configuration of the major product 12 was confirmed by X-ray structure analysis. Epoxidation and subsequent cyclization afforded the cis and trans diastereomers 19 and 20, respectively, in a 1:1 ratio. Subsequent cleavage of the protecting groups and separation of the isomers furnished the target compounds in good overall yields.