The preparation of a dimannosyl[c2]daisy chain molecular machine containing an ammonium and a triazolium station is described. The both stretched and contracted states of the molecular machine can be obtained by variation of the pH, thus localizing the mannosyl stoppers closer or farther away.

No abstract

Ring of protection: A [2]rotaxane 1 protects and selectively releases a bioactive pentapeptide. The rotaxane macrocycle provides a defensive shield that very significantly improves the poor stability of the peptide to both individual peptidases and the cocktail of enzymes present in human plasma. Glycosidase‐catalyzed cleavage of a carbohydrate ‘stopper’ in the rotaxane triggers release of the parent peptide (see picture).

The control of motion of one element with respect to others in an interlocked architecture allows for different co-conformational states of a molecule. This can result in variations of physical or chemical properties. The increase of knowledge in the field of molecular interactions led to the design, the synthesis, and the study of various systems of molecular machinery in a wide range of interlocked architectures. In this field, the discovery of new molecular stations for macrocycles is an attractive way to conceive original molecular machines. In the very recent past, the triazolium moiety proved to interact with crown ethers in interlocked molecules, so that it could be used as an ideal molecular station. It also served as a molecular barrier in order to lock interlaced structures or to compartmentalize interlocked molecular machines. This review describes the recently reported examples of pH-sensitive triazolium-containing molecular machines and their peculiar features.

The syntheses of various two- and three-station mannosyl [c2]daisy chains, based on a dibenzo-24-crown-8 macrocyclic moiety and an ammonium, a triazolium, and a mono- or disubstituted pyridinium amide station, are reported. The ability of these molecules to act as molecular machine based mimetics has been further studied by (1)H NMR studies. In all the protonated ammonium states, the interwoven rotaxane dimers adopt an extended co-conformation. However, carbamoylation of the ammonium station led to many different other [c2]daisy chain co-conformations, depending on the other molecular stations belonging to the axle. In the two-station [c2]daisy chains containing an ammonium and a mono- or disubstituted pyridinium amide station, two large-amplitude relative movements of the interwoven components were noticed and afforded either an extended and a contracted or very contracted state with, in the latter case, an impressive chairlike conformational flipping of the mannopyranose from (1)C(4) to (4)C(1). In the case of the three-station-based [c2]daisy chains containing an ammonium, a triazolium, and disubstituted pyridinium amide, an extended and a half-contracted molecular state could be obtained because of the stronger affinity of the dibenzo-24-crown-8 part for, respectively, the ammonium, the triazolium, and the disubstituted pyridinium amide. Eventually, with axles comprising an ammonium, a triazolium, and a monosubstituted pyridinium amide, an extended conformation was noticed in the protonated state whereas a continuous oscillation between half-contracted and contracted states, in fast-exchange on the NMR time scale, was triggered by carbamoylation. Variations of the solvent or the temperature allow the modification of the population of each co-conformer. Thermodynamic data provided a small free Gibbs energy ΔG of 2.1 kJ·mol(-1) between the two translational isomers at 298 K.

Schützender Ring: Das [2]Rotaxan 1 kann ein bioaktives Pentapeptid schützen und selektiv freisetzen. Der Makrocyclus des Rotaxans stabilisiert das empfindliche Peptid sowohl gegen einzelne Peptidasen als auch gegen eine Enzymmischung aus Humanplasma. Die durch Glycosidase katalysierte Abspaltung einer Kohlenhydrat‐Endgruppe, die im Rotaxan als Stopper wirkt, führt zur Freisetzung des Peptids (siehe Bild).

El artículo seleccionado no se encuentra disponible por ahora a texto completo por no haber sido facilitado todavía por el investigador a cargo del archivo del mismo.

The transmission of information is ubiquitous in nature and often occurs through supramolecular hydrogen bonding processes. Here we report that there is a remarkable correlation during synthesis between the efficiency of the hydrogen-bond-directed assembly of peptide-based [2]rotaxanes and the symmetry distortion of the macrocycle in the structure of the final product. It transpires that the ability of the flexible macrocycle-precursor to wrap around an unsymmetrical hydrogen bonding template affects both the reaction yield and a quantifiable measure of the symmetry distortion of the macrocycle in the product. When the yields of peptide rotaxane-forming reactions are high, so is the symmetry distortion in the macrocycle; when the yields are low, indicating a poor fit between the components, the macrocycle symmetry is relatively unaffected by the thread. Thus during a synthetic sequence, as in complex biological assembly processes, hydrogen bonding can code and transmit ''information''-in this case a distortion from symmetry-between chemical entities by means of a supramolecularly driven multicomponent assembly process. If this phenomenon is general, it could have far reaching consequences for the use of supramolecular-directed reactions in organic chemistry.continuous symmetry measure ͉ hydrogen bonds ͉ molecular recognition ͉ rotaxanes ͉ symmetry distortion