Rigid duplex alpha-cyclodextrin reversibly connected with disulfide bonds. Synthesis and inclusion complexes.
The rigid duplex cyclodextrin 6 composed of two alpha-cyclodextrin macrocycles connected with two disulfide bonds in "transannular" (C6(I), C6(IV)) positions was prepared from partially debenzylated alpha-cyclodextrin 1 in four steps in 73% overall yield. In the last key step involving oxidative coupling of the thiol 5, predominance of the target duplex 6 can be attained under conditions of thermodynamic control. The structure of duplex cyclodextrin was established by MS as well as 2-D NMR methods and confirmed by a single-crystal X-ray analysis. The ability of the duplex cyclodextrin 6 to bind alpha,omega-alkanediols (C9-C14) and 1-alkanols (C9 and C10) was studied by isothermal titration calorimetry in aqueous solutions. The stability constants of the complexes gradually increase with the alkyl chain length and reach an unprecedently high value of K = 8.6 x 10(9) M(-1) for 1,14-tetradecanediol. It was found that the doubly bridged dimer 6 exhibits higher binding affinity toward the series of alpha,omega-alkanediols than the singly bridged analogue 10 by about 2 orders of magnitude in K (M(-1)) or 3.1-3.3 kcal/mol in deltaG(o), the enhancement being due to enthalpic factors. Theoretical calculations using DFT-D methods suggest that the enthalpic contribution stems from dispersion interactions.
Kumprecht
Lukás
L
Institute of Organic Chemistry and Biochemistry AS CR, v.v.i. Flemingovo nám. 2, 166 10 Praha 6, Czech Republic.
Budesínský
Milos
M
Vondrásek
Jirí
J
Vymetal
Jirí
J
Cerný
Jirí
J
Císarová
Ivana
I
Brynda
Jirí
J
Herzig
Vladimír
V
Koutník
Petr
P
Závada
Jirí
J
Kraus
Tomás
T
D000438:Alcohols / Q000737:chemistry; D018360:Crystallography, X-Ray; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry*; D008958:Models, Molecular; D008968:Molecular Conformation; D013816:Thermodynamics; D047391:alpha-Cyclodextrins / Q000138:chemical synthesis / Q000737:chemistry*
D000438:Alcohols; D004220:Disulfides; D047391:alpha-Cyclodextrins; C032613:alpha-cyclodextrin