title: Molecular Architecture and Symmetry Properties of 1,3-Alternate Calix[4]arenes with Orientable Groups at the Para Position of the Phenolic Rings.
abstract: Two glycoclusters constituted by four fully acetylated β-acetylmannosamine residues linked through trimethylenethioureido spacers to a calix[4]arene core and differing for the presence of methoxy or propoxy groups at the lower rim were synthesized. One of the two compounds is fixed in the 1,3-alternate geometry by the presence of the propoxy groups, while the other is potentially free to assume one of the different geometries allowed in calix[4]arene. Their similar NMR spectra in chloroform clearly suggest the same 1,3-alternate geometry. Both compounds were submitted to a conformational investigation with the DFT approach at the standard B3LYP/6-31G(d) level. The two glycocalixarenes showed a large conformational preference for the same geometry that put the mannosamine moiety of one substituent close to the thioureido group of the opposite substituent. This allows the formation of intramolecular hydrogen bonds and originates a series of through-space close contacts. A comparison with the NOESY maps evidence an excellent correspondence between experimental and theoretical data, thus giving an experimental validation of the highly symmetrical conformation that the two glycocalixarenes assume in apolar solvents.
authors.affiliation: Dipartimento di Chimica, Università di Pavia , Via Taramelli 12, 27100 Pavia, Italy.
authors.forename: Lucio
authors.initials: L
authors.lastname: Toma
authors.affiliation: Dipartimento di Chimica, Università di Pavia , Via Taramelli 12, 27100 Pavia, Italy.
authors.forename: Laura
authors.initials: L
authors.lastname: Legnani
authors.affiliation: Dipartimento di Biotecnologie Mediche e Medicina Traslazionale, Università di Milano , Via Saldini 50, 20133 Milano, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Compostella
authors.affiliation: Dipartimento di Chimica, Università di Parma , Parco Area delle Scienze 17/A, 43124 Parma, Italy.
authors.forename: Marta
authors.initials: M
authors.lastname: Giuliani
authors.affiliation: Dipartimento di Chimica, Università di Parma , Parco Area delle Scienze 17/A, 43124 Parma, Italy.
authors.forename: Federica
authors.initials: F
authors.lastname: Faroldi
authors.affiliation: Dipartimento di Chimica, Università di Parma , Parco Area delle Scienze 17/A, 43124 Parma, Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Casnati
authors.affiliation: Dipartimento di Chimica, Università di Parma , Parco Area delle Scienze 17/A, 43124 Parma, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Sansone