The physiological properties of the higher monosaccharides and their derivatives (for example, the sialic acids) make them attractive targets for synthetic modification and structural studies. The products of such investigations could be useful in determining correlations between molecular structure and biological function. Thus, the synthesis of such higher-carbon sugars as heptoses'**, heptitols3, octoses4.5, nonoses6, and decoses7,8 has recently received considerable attention. Higher-carbon sugars have been used in the synthesis of mycin-type antibiotics4*9s'0 and chiral segments of macrolides". Thus far, conformational analysis of higher-carbon sugars has been very limited. Angyal and co-workers'2'13 have studied the conformations of heptitols; however, there appear to be no reports of similar studies of octitols, octuloses, or other higher-carbon sugars.
The aim of this paper is to discuss, at length, the structures and conformations of 2,7-anhydro-L-glycero-P-D_manno-octulopyranose
(3) and 1,3,4,5,8-penta-0-acetyl-2, 7-anhydro-L-g&zero-fi-o-munno-octulopyranose (4). Richtmyer reported the preparation of 3 from D-erythro-D-galucto-octitol (1) which had been isolated from avocado'4"5. Oxidation of 1 with Acetobacter suboxydans, followed by treatment of the resulting syrupy L-glycero-D-manno-octulose
(2) with methanol in the presence of a cationexchange resin, yielded a product that was presumed to be 3 on the basis of the mass spectrum of its per-U-trimethylsilyl derivative (molecular ion at m/z 582) and the absence of formaldehyde on treatment of the product with periodate14. Our examination of 3 and 4, using both 'H-and r3C-n.m.r. spectroscopy, has confirmed the structure originally assigned by Richtmyer.
The 'H-n.m.r. spectrum of the penta-acetate 4 in chloroform-d at 400 MHz displayed five resonances for acetyl methyl protons and a well dispersed, sugar-chain proton region, first-order analysis of which yielded the chemical shifts reported in Table * Dedicated to Professor Leslie Hough in the year of his 65th birthday.