OLIGOSACCHARIDE ANALOGS OF POLYSACCHARIDES .12. SYNTHESIS OF ACETYLENO-SACCHARIDE-DERIVED CYCLODEXTRIN ANALOGS

Acetyleno-oligosaccharides in which two terminal ethynyl substituents enclose an angle (significantly) below 180 degrees are building blocks for the preparation of cyclodextrin analogues. This is illustrated by the preparation of a cyclotrimer and a cyclotetramer; the C-3-symmetr ical cyclotrimer 18 (Scheme I) was synthesized in 13 steps (7.7%) and the C-4-symmetrical cyclotetramer 51 (Scheme 3) in 14 steps (4.3%) fro m the known dialkyne 21. The solubilities of 18 and 51 in H2O were det ermined by gravimetry; a saturated solution is 130 mM in the trimer 18 and 12.8 mM in the tetramer 51. The dependence of the optical rotatio n of 18 and 51 in H2O on the concentration, and the concentration depe ndence of the H-1-NMR chemical shift of the signals of the CH groups o f 51 (D2O) suggest that there is no significant self-association of 18 and 51.