Controlling Swing Rates in Macrocyclic Molecular Mortise Hinges

Abstract

Hinge motion is observed in macrocyclic, mortise‐type molecular hinges using variable temperature NMR spectroscopy. The data is consistent with dynamic hinging from a folded‐to‐extended‐to‐folded enantiomeric state. Crystallographic and solution structures of the folded states are reported. Chemical shift predictions derived from crystallographic data corroborate fully revolute hinge motion. The rate of hinging is affected by steric congestion at the hinge axis. A macrocycle containing glycine, 1, hinges faster than one comprising aminoisobutyric acid, 2. The free energies of activation, ΔG≠, for 1 and 2 were determined to be 13.3±0.3 kcal/mol and 16.3±0.3 kcal/mol, respectively. This barrier is largely independent of solvent across those surveyed (CD3OD, CD3CN, DMSO‐d6, pyridine‐d5, D2O). Experiment and computation predict energy barriers that are consistent with disruption of an intramolecular network of hydrogen bonds. DFT calculations reveal a pathway for hinge motion.

Proton Affinity and Conformational Integrity of a 24-Atom Triazine Macrocycle across Physiologically Relevant pH

“…Recently, we reported the use of dynamic covalent chemistry to make macrocycles based on the dimerization of a monomer that presents both acetal and hydrazine groups. − As the ring size increases from 22 to 28 atoms, the shapes of these molecules evolve from stepped to saddle to sheet to crinkled sheet . The saddle-shaped, 24-atom macrocycles attracted our initial interest for many reasons.…”

Impact of Solvent and Protonation State on Rotational Barriers in [s]-Triazines

“…Our interest in the rotational barriers of the triazine-N bond stems from a recent focus on their inclusion in macrocycles. − The macrocyclization performed is an acid-catalyzed dimerization that produces protonated triazines. In most cases, the reaction is quantitative and a single, symmetric isomer is obtained, likely due to a proton-mediated hydrogen bond network …”

“…Recently, some of these protonated molecules have displayed dynamic hinge motion attributed to flexible domains within the macrocycle . The Δ G ‡ for hinging ranged from 13.1 to 15.5 kcal/mol depending on steric congestion.…”

Adaptation of Empirical Methods to Predict the LogD of Triazine Macrocycles

“…Here we evaluate the abilities of AlogP, XlogP, and ChemAxon to predict the logD of a family of macrocycles that adopt similar conformations in solution. − More extensive comparisons of these and other algorithms have been reported. In a critical review of the impact of Lipinski’s rules on drug discovery, Schultz evaluated the ability of six empirical methods to accurately predict logP for 453 FDA-approved drugs and four methods against a Novartis collection of 3667 compounds .…”