Very Contracted to Extended co-Conformations with or without Oscillations in Two- and Three-Station [c2]Daisy Chains

Abstract

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.

Remote electrochemical modulation of pK a in a rotaxane by co-conformational allostery

“…Such a phenomenon, that can be rationalized with both thermodynamic and kinetic arguments, is in line with earlier observations (22)(23)(24)(25)(26) that deprotonation of ammonium axles in crown etherbased rotaxanes is extremely difficult to achieve. We also found that the decrease of acid strength is mitigated in the presence of an alternative recognition site for the ring.…”

<i>N</i>-Methylniphatyne A, a New 3-Alkylpyridine Alkaloid as an Inhibitor of the Cancer Cells Adapted to Nutrient Starvation, from an Indonesian Marine Sponge of <i>Xestospongia</i> sp.

“…We anticipated that N-methylniphatyne A (1) could be easily elaborated through the coupling between lithium acetylide derived from an aminoalkyne and a pyridylalkyl bromide, as depicted in Chart 1. Aminoalkyne 4a (m=3) was prepared from 8-bromo-1-octyne (3a) 22) and N,O-dimethylhydroxylamine hydrochloride in the presence of Et 4 NI and K 2 CO 3 . Pyridylalkyl bromide 5a (n=3), another fragment, was synthesized through the reported procedure.…”

“…N,O-Dimethyl-N-(oct-7-yn-1-yl)hydroxylamine (4a) K 2 CO 3 (498 mg, 3.60 mmol), N,O-dimethylhydroxylamine hydrochloride (351 mg, 3.60 mmol) and Et 4 NI (35 mg, 0.14 mmol) were succesively added to a solution of 8-bromooct-1-yne (3a, 280 mg, 1.48 mmol) 22) in 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU, 3 mL), and the reaction mixture was stirred at room temperature (r.t.) for 3 h and at 60°C for 9 h. Sat. NH 4 Cl aq.…”

Rotaxanes and pseudorotaxanes with threads containing pyridinium units

“…The both rings become situated at N-methyltriazolium stations, since each ring has higher affinity to N-methyltriazolium than to the disubstituted pyridinium amide station. 91 …”

“…ammonium, substituted pyridinium amide and Nmethyltriazolium. 91 It was found that in the case of protonated ammonium stations the daisy chains adopt the extended co-conformation (Scheme 15). The deprotonation/carbamoylation process of 61a,b and 62a,b was performed by using diisopropylethylamine (DIEA) and di-t-butyl dicarbonate (Boc 2 O).…”