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Oligosaccharide Analogues of Polysaccharides, Part 17, Synthesis and Characterization of a Hexadecamer: Evidence for the Essential Structural Role of the Intramolecular, Interresidue C(3)−OH⋅⋅⋅O−C(5) Hydrogen Bond in Celluloses
Author(s) -
Bohner Tanja Verena,
Becker OlavSven,
Vasella Andrea
Publication year - 1999
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/(sici)1522-2675(19990210)82:2<198::aid-hlca198>3.0.co;2-y
Subject(s) - chemistry , histone octamer , intramolecular force , dimer , monomer , crystallography , hydrogen bond , yield (engineering) , stereochemistry , polymer , organic chemistry , molecule , biochemistry , materials science , nucleosome , metallurgy , gene , histone
The hexadecamer 63 dissolves readily in DMSO and shows no sign of association, in agreement with the essential structural role of the intramolecular, interresidue C(3)−OH⋅⋅⋅O−C(5) H‐bond of celluloses. MM3 Calculations predict a rod‐like shape for the cello‐oligosaccharides. In agreement with this, nanocrystalline domains of parallel chains are observed by high‐resolution electron microscopy (HREM) for 54 and 63 on carbon‐coated copper grids. For the synthesis of the hexadecamer 54 , we studied the influence of protecting groups on the cross‐coupling of acetyleno‐oligosaccharides and on their solubility ( Scheme 2 ). The octamer 12 derived from the minimally O ‐protected monomer 2 is insoluble, while the methoxymethyl‐ and triisopropylsilyl‐protected hexadecamer 54 , prepared in twelve steps from the dimer 41 ( Scheme 4 ), is readily soluble in a variety of solvents. O ‐ and C ‐deprotection of 54 led in four steps and in 76% yield to the hexadecamer 63 ( Schemes 5 and 6 ). There is only a small difference of spectroscopic properties between the protected octamer 50 and hexadecamer 54 , and, similarly, between the unprotected octamer 64 and hexadecamer 63 ( Fig. 3 ).