(RSS)-[N-Hydroxyethyloxy]-hexafluoroVal–MeLeu–Ala tert-butyl ester

The title compound [systematic name: (2S,5S,8R)-tert-butyl 8-(1,1,1,3,3,3-hexafluoropropan-2-yl)-12-hydroxy-5-isobutyl-2,6-dimethyl-4,7-dioxo-10-oxa-3,6,9-triazadodecanoate], C21H36F6N3O6, is a tripeptide crystallizing in the chiral ortho­rhom­bic spacegroup P212121. The absolute configuration (R) of the chiral center in the hexa­fluoro­valine unit is based on the known stereochemistry of MeLeu and Ala (SS). The N-hydroxy­ethyl­oxy substituent of hexa­fluoro­valine is positionally disordered [occupancy ratio 0.543 (9):0.457 (9)]. In the solid state structure there are N—H⋯F and N—H⋯O intra­molecular hydrogen bonds supporting the coiled structure of this tripeptide with the three hydro­phobic substituents on the outside

The quest for planarizing distortions in hydrocarbons: two stereoisomeric 4.5.5.5 fenestranes

According to semiempirical calculations the planarizing distortions in the central C(C)4 substructure of fenestranes, represented as 1, can be enhanced by a variety of structural modifications. Based on these results we selected the 7-hydroxy-c,c,c,c- and c,t,c,c[4.5.5.5]fenestranones 13 and 16 as precursors for the introduction of a bridgehead double bond. The efficient synthesis of these precursors and their chemical transformations are reported. Attempts to activate the hydroxyl group in 16 for introduction of a bridgehead double bond led to the rearrangement of the [4.5.5.5]fenestrane to a triquinacane skeleton. (C) 2011 Elsevier Ltd. All rights reserved