Chemistry of 5-oxodihydroisoxazoles .18. Synthesis of oxazoles by the photolysis and pyrolysis of 2-acyl-5-oxo-2,5-dihydroisoxazoles

N-Acylisoxazol-5-ones lose carbon dioxide under photochemical and thermal conditions affording iminocarbenes which undergo intramolecular cyclisation through the oxygen of the acyl group to give oxazoles. Under photochemical conditions those acylisoxazolones with electron withdrawing groups at C-4 usually give high yields of oxazoles, while those with electron donating groups at C-4 give only poor yields: the reverse is observed under thermal conditions.

Regioselective synthesis of antiparallel loops on a macrocyclic scaffold constrained by oxazoles and thiazoles

[GRAPHICS] The regioselective syntheses and structures are reported for two tris-macrocylic compounds, each possessing two antiparallel loops on a macrocyclic scaffold constrained by two oxazoles and two thiazoles. NMR solution structures show the loops projecting from the same face of the macrocycle. Such molecules are shown to be prototypes for mimicking multiple loops of proteins.

Structural mimicry of two cytochrome b(562) interhelical loops using macrocycles constrained by oxazoles and thiazoles

A major chemical challenge is the structural mimicry of discontinuous protein surfaces brought into close proximity through polypeptide folding. We report the design, synthesis, and solution structure of a highly functionalized saddle-shaped macrocyclic scaffold, constrained by oxazoles and thiazoles,upporting two short peptide loops projecting orthogonally from the same face of the scaffold. This structural mimetic of two interhelical loops of cytochrome b(562) illustrates a promising approach to structurally mimicking discontinuous loops of proteins.

Chemistry of 5-oxodihydroisoxazoles .17. Acylation of 5-oxodihydroisoxazoles

2-Unsubstituted isoxazol-5(4H)-ones and -5(2N)-ones may be acylated by acid chlorides, anhydrides or carboxylic acids in the presence of carbodiimides, to give O- and N-acylated products, The solvent, the presence of base and the temperature are found to alter the product ratios dramatically, but the substituents present at C-3 have the greatest effect, Aliphatic acid anhydrides and chlorides generally react at nitrogen, but aroyl halides give significant proportions of O-acylated products, Limited success in converting O-aroyl to N-aroyl isoxazolones is reported.