Premium
Solid State and Solution Conformation of 6‐{4‐[ N‐tert ‐Butoxycarbonyl‐ N ‐( N′ ‐ethyl)propanamide]imidazolyl}‐6‐deoxycyclomaltoheptaose: Evidence of Self‐Inclusion of the Boc Group within the β‐Cyclodextrin Cavity
Author(s) -
Impellizzeri Giuseppe,
Pappalardo Giuseppe,
D’Alessandro Franca,
Rizzarelli Enrico,
Saviano Michele,
Iacovino Rosa,
Benedetti Ettore,
Pedone Carlo
Publication year - 2000
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/1099-0690(200006)2000:12<2345::aid-ejoc2345>3.0.co;2-a
Subject(s) - chemistry , moiety , intramolecular force , crystallography , hydrogen bond , cyclodextrin , amide , stereochemistry , nuclear magnetic resonance spectroscopy , circular dichroism , aqueous solution , pendant group , molecule , organic chemistry , polymer
A new modified β‐cyclodextrin (β‐CD) derivative 1 that was functionalized in position 6 with Boc‐Carcinine was synthesised and its crystal structure was determined. The structure reveals a ‘‘sleeping swan’’‐like shape, the covalently bonded Boc‐Carcinine moiety forming a folded structure with the Boc group inserted within the hydrophobic cavity of the β‐cyclodextrin. The conformation of the Carcinine moiety is determined by the inclusion of the Boc group and is further stabilised by three intramolecular hydrogen bonds, two between the amide N1–H group, the carbonyl C′1=O1 group and a primary hydroxylic group of the glucose unit 5, one between the carbonyl C′0=O0 group and the primary hydroxylic group of the glucose unit 2. The β‐CD macrocycle differs only slightly from unmodified β‐CDs, maintaining an approximate sevenfold symmetry. The solution structure of the new β‐CD derivative was investigated by NMR spectroscopy and circular dichroism (c.d.) spectroscopy. In addition to a complete ( 1 H and 13 C) assignment of the pendant Boc‐Carcinine group, the NMR study allowed the assignment of all the proton resonances associated with the β‐CD macrocycle. Furthermore, NMR and c.d. results indicated that the self‐inclusion of the Boc group within the β‐CD cavity is retained in aqueous solution. In order to estimate the strength of this self‐inclusion complex a series of competition experiments with the external guest 1‐adamantanol was carried out using c.d. spectroscopy.