title: Acyclic congener of cucurbituril: synthesis and recognition properties.
abstract: The cucurbit[n]uril (CB[n]) family of macrocycles occupies a prominent role in molecular recognition and self-assembly studies despite the current inability to access specific cucurbit[n]uril homologues, derivatives, and analogues by straightforward tailor-made synthetic procedures. In this paper, we explore an approach that circumvents the challenges posed by the tailor-made synthesis of macrocyclic CB[n] by preparing 1, which functions as an acyclic CB[6] congener. The o-xylylene connections to the glycoluril rings preorganize 1 into the (a,a,a,a)-1 conformation required for binding and reduce its tendency to undergo self-association. We surveyed the binding properties of 1 toward 16 amines (K(a) <or= 1.52 x 10(4) M(-)(1)) and diol, diacid, guanidinium, and pyridinium species in pD 7.4 phosphate-buffered D(2)O. We find that the recognition properties of 1 parallel those of CB[6], binding tightly to alkaneammonium species in water and exhibiting length-dependent selectivity and competitive binding with alkali metals present in solution. Compound 1 binds hexanediammonium ion only 180-fold less tightly than CB[6]. The modular synthesis of 1 suggests synthetic methods toward the preparation of acyclic CB[n] congeners with complex functional groups on the edges of their aromatic rings and cavity volumes similar to CB[7] and CB[8]. In combination, these results suggest that acyclic CB[n] congeners hold promise in molecular recognition and self-assembly studies that complements that of macrocyclic CB[n].
authors.affiliation: Department of Chemistry and Biochemistry, University of Maryland, College Park, College Park, Maryland 20742, USA.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Burnett
authors.forename: Dariusz
authors.initials: D
authors.lastname: Witt
authors.forename: James C
authors.initials: JC
authors.lastname: Fettinger
authors.forename: Lyle
authors.initials: L
authors.lastname: Isaacs
mesh_terms: D001952:Bridged-Ring Compounds / Q000138:chemical synthesis* / Q000737:chemistry*; D002021:Buffers; D018360:Crystallography, X-Ray; D015195:Drug Design; D007093:Imidazoles / Q000138:chemical synthesis* / Q000737:chemistry*; D007202:Indicators and Reagents; D007700:Kinetics; D008958:Models, Molecular; D008968:Molecular Conformation; D013816:Thermodynamics; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils
chemical_list: D001952:Bridged-Ring Compounds; D002021:Buffers; D007093:Imidazoles; D007202:Indicators and Reagents; C454805:cucurbit(6)uril; D047028:Macrocyclic Compounds; D000099246:Cucurbit(n)urils