Synthesis and biological evaluation of 1,7,8,8a-tetrahydro-3H-oxazolo[3,4-a]pyrazin-6(5H)-ones as antitumoral agents

A series of 1,7,8,8a-tetrahydro-3H-oxazolo[3,4-a]pyrazin-6(5H)-ones has been synthesized by an intramolecular, palladium(II) catalyzed, aminooxygenation of alkenyl ureas, readily available from glycine allylamides as starting materials. Biological tests showed that the obtained compounds are endowed with an interesting antitumoral activity against two human thyroid cancer cell lines, namely FTC-133 and 8305C, by promoting the apoptotic pathway and DNA fragmentation.     

Synthesis and conformational analysis of cyclo-TRI[l-valyl-d-hexahydromandelyl]

The synthesis of the cyclo-hexadepsipeptide [l-valyl-d-hexahydromandelyl]₃ is described. Examination of this macrocyclic compound by 220-MHz nuclear magnetic resonance spectroscopy shows that symmetrical conformations are stabilized in strongly polar solvents (trifluoroacetic acid, acetonitrile), whereas asymmetric conformations are preferred in nonpolar or slightly polar media such as carbon tetrachloride, chloroform, cyclohexane, and benzene.From analysis of the temperature dependence of the chemical shift and of the coupling constants, together with conformational energy calculations, a model is proposed for the preferred conformation of this molecule in nonpolar solvents.