Alkali metal ions as probes of structure and recognition properties of macrocyclic pyridyl urea hosts.

We report the one-pot synthesis of three symmetrical macrocyclic pyridyl urea hosts. X-ray crystal studies were used to confirm the structures of the free hosts and their host.guest complexes with alkali metal ions. These solid-state studies revealed the interactions that were important for binding cations (Li(+), Na(+), and K(+)). The affinity of these hosts for alkali metal salts were evaluated in solution (CD(3)CN), and the stoichiometries of the solution complexes were compared with their solid-state structures. Two of these hosts showed high affinity for LiBF(4), which was primarily due to strong interactions between the urea oxygens and the cations with pyridine nitrogens contributing additional stabilizing interactions.

Guest induced transformations of assembled pyridyl bis-urea macrocycles.

Pyridine macrocycles with no cavities assembled into close packed columns yet absorbed guests including hydrogen, carbon dioxide, and iodine.

A divergent approach to the preparation of cysteine and serine analogs.

Malonate diesters containing a prochiral quaternary carbon have been successfully transformed into analogs of cysteine and serine. The chiral half-esters are obtained in good yield, and enantioselectivity by selective hydrolysis using Pig-Liver Esterase (PLE) as the catalyst. The resulting half-ester intermediates are transformed into alpha2, 2-, beta2, 2-, and beta3, 3-analogs of cysteine and serine. The methodology described here allows for the preparation of both enantiomers of the amino-acid analogs by selective manipulation of the ester and acid functionalities. This divergent strategy allows a common synthetic strategy to be used to prepare a variety of unnatural amino-acid classes from a common intermediate which should prove useful in the design of novel peptide libraries.