Oligosaccharide analogues of polysaccharides - Part 21 - Towards new cellulose I mimics: Synthesis of dialkynyl C-glucosides of peri-substituted anthraquinone

The bis-C-glucoside 2 has been synthesised as the first representative of a series of templated glucosides and cellooligosaccharides that mimick part of the unit cell of cellulose I. As expected, there are, at best, weakly pe rsistent H-bond between the two glucosyl residues in (D-6)DMSO and (D-7)DMF solution. The acetylated oct-1-ynitol 7 and deca-1,3-diynitol 12 were prep ared from the gluconolactone 5 (Scheme 1). Coupling of 12 to Phl and 2-iodo thiophene yielded 13 and 14, respectively, while dimerisation of the benzyl ated and acetylated deca-1,3-diynitols 10 and 12 afforded the bis-C-glucosy loctatetrayne 15 and the less stable 16, respectively. The 2-glucosylthioph ene 17 was obtained by treating the C-silylated deca-1,3-diynitol 9 with Na 2S. Cross-coupling of 9trimethylsilyl)acetylene (TMSA) with 1,8-bis(trifylo xy)-9,10-anthraquinone (20) at elevated temperature gave the dialkynylated 21; its structure was established by X-ray analysis (Scheme 2). Sequential coupling of 6 or 7 and TMSA to 20 gave the symmetric dialkyne 21, the mixed dialkynes 23 (from 6) and 25 (from 7), and the symmetric diglucoside 36 (f rom 7) in modest yields; a stepwise coupling to the acetylated monotriflate 28 proved advantageous. It led to the oct-1-ynitol 29 and the deca-1,3-diy nitol 33 that were tranformed into the triflates 30 and 34, respectively. C oupling of the triflate 34 to the oct-1-ynitol 7 gave the unsymmetric bis-C -glucoside 35; this was obtained in higher yields by coupling the triflate 30 to the deca-1,3-diynitol 12. Coupling of the bistriflate 20 with either 7 or 12 afforded the symmetric bis-C-glucosides 36 and 37, respectively. De acetylation (KCN in MeOH) of 35-37 provided the unsymmetric bis-C-glucoside 2 and the symmetric analogues 3 and 4.