Crystal structures of two isomorphous solvates of the macrolide antibiotic borrelidin [ borrelidin 3-methylbutan-1-ol (A) and borrelidin (S)-2-methylbutan-1-ol (B)] have been determined from X-ray diffractometer data recorded at 294 and 152 K respectively. Crystals are monoclinic, space group P21, with a 13.501(2), b 12.000(2), c 11.863(2) � , β 110.76(1)� [(A); T = 294 K], and a 13.565(2), b 11.646(2), c 11 .376(3) �, β 109.76(1)� [(B); T = 152 K], (Z = 2). The structures were solved by direct-methods procedures and refined by full-matrix least-squares analysis to conventional R-factors of 0.061 [(A), 2676 reflections] and 0.048 [(B), 2851 reflections]. The absolute configuration of borrelidin follows from the known chirality of the (S)-2-methylbutan-1-ol solvent in (B), and is 3S,4S,6S,8R,1OS,11R,17S,18R,22R. The unusual structural and stereochemical features of borrelidin are discussed in relation to other macrolide antibiotics.
Efficient syntheses are
reported of the natural amino acid 3-amino-5-hydroxybenzoic
acid in unlabelled and carboxyl-labelled forms from 3,5-dinitrobenzoic acid
and 3,5-dinitroanisole, respectively.
Die nicht markierte Titelverbindung (VII) wird ausgehend vom Anion der Dinitrocarbonsäure (V) erhalten, das mit Li‐methylat in siedendem Methanol die Methoxycarbonsäure (III) quantitativ liefert, während der Ester (I) mit Li‐methylat ein Gemisch der Verbindungen (II), (III) und (IV) liefert.
The structure and absolute configuration (3) of the biologically active ansamycin antibiotic awarnycin have been determined from X-ray diffraction data recorded at 129 K. Crystals are monoclinic, space group P2′2′2′, with a 25.426(3), b 30.823(2), c 13.592(1) A, and contain two molecules of the antibiotic and eleven solvent molecules (two water and nine ethanol) in each asymmetric scattering unit. The structure was solved with SHELXS and refined by full-matrix least-squares analysis to R 0.076 ( Rw 0.090) for 7308 reflections and 1174 refined parameters. Analysis of observed and calculated Bijvoet differences with the statistic Χ2 defines the absolute configuration of awamycin as 20R,21R,22R,23R,24R,25R,26R,27S,28S and the helicity as P. This is the first crystal structure analysis of an underivatized ansamycin antibiotic of the subgroup possessing an 18-membered ansa chain, and the first such analysisof an underivatized ansarnycin antibiotic in which it has been possible to assign absolute stereochemistry by the Bijvoet method. The constitution and absolute configuration of awamycin are compared with those of related ansarnycins carrying 18- and 19-membered ansa chains, and the tertiary structures of awarnycin and of several rifamycins and variants are analysed in relation to the arrangement of oxygen functions required for antibiotic activity.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.