Mettler-Toledo (China)

Because of the importance of helices in the secondary structure of proteins, we have undertaken a study of their spectroscopy, fragmentation patterns and conformations in the gas phase. In this work, we describe the effects of substitution at the N-terminus of polyalanine helices capped with a lysine at the C-terminus, namely Ac-Phe-(Ala)10-Lys-H+, Phe-(Ala)10-Lys-H+, and H+-Phe-(Ala)10-Lys-H+. Acetylation of the N-terminus has very little effect on the spectroscopy and structure, but protonation of the N-terminus changes the infrared spectrum in such a way that we believe it may also change the structure of the peptide. The ultraviolet spectroscopy and fragmentation, on the other hand, are insensitive to either acetylation or protonation.

The development of efficient routes to multi-gram quantities of chiral synthons is a key issue in the total synthesis of natural products and analogues. The conformationally defined and rigid 8-oxabicyclo[3.2.1]oct-6-en-3-one template is an appealing starting material for the development of non-iterative approaches to polyoxygenated fragments that are found in a large variety of biologically relevant natural compounds. Desymmetrization and resolution procedures, stereoselective functionalizations and double-chain elongations represent attractive strategies for such synthetic challenges.