MOLECULAR-STRUCTURE OF A NEW POLYMORPH OF THE K+, RB+ CHELATE OF MESOVALINOMYCIN

The crystal structure of a new polymorph of hydrated mesovalinomycin c yclo[-(D-Val-L-Hyi-L-Val-D-Hyi)(3)](1) (C60H102N6O18) was solved by th e direct methods, sp. gr. P1, Z = 2, unit-cell parameters a = 14.08, b = 14.48, c = 22.63 Angstrom, alpha = 95.48 degrees, beta = 68.32 degr ees, gamma = 119.06 degrees. Upon refinement, the standard R factor wa s 0.109. It was established that, in this modification as well, both i ndependent molecules of mesovalinomycin adopt a rather rigid bracelet conformation with a negatively charged inner cavity and six intramolec ular hydrogen bonds. The structural parameters of all the known crysta lline modifications of mesovalinomycin are analyzed.