Crystal and molecular structure of showdomycin

Abstract

The crystal structure of showdcmycin, C9H1,N06, has been determined by a thres-dimensional X-ray analysis.The crystals are monoclinic, a = 1 5.454, b = 6-547, c = 11.425, p = 121 "1 6'. Z = 4, space group C2. The intensities were measured with a Hilger and Watts automatic four-circle diffractometer using Mo-K, radiation. The structure was solved by the symbolic addition procedure for phase determination as applied to noncentrosymmetric crystals, and refined by full-matrix least-squares calculations to a final R of 0-050 for 1092 independent observed reflexions. Atom C(2') of the sugar residue is displaced by ca. 0.58 a from the least-squares plane through the other four ring atoms and lies on the same side of the plane a t C(5'). This plane also makes an angle of ca. 46" with the least-squares plane through the five atoms of the pyrroline ring. The torsion angle with respect to the glycosidic bond, according to the Sundaralingam and Jensen definition, is 129.5". and the conformation therefore is syn. Osaka, Japan3-(P-~-ribofuranosyl)-3-pyrroline-2,5-di-No absorption corrections were applied since the specimen one, an antibiotic,"C,H,1N06, was first isolated from Streptowzyces showdoensis. A number of studies of showdomycin (I) 2-4 and its derivative (11) 5 have been reported, but no details of the stereochemistry of showdomycin have yet been given. The present X-ray study was therefore undertaken to obtain molecular conformational information on the structure of showdomycin.

Structure and conformation of the hydrochloride of pseudoisocytidine, an antileukemic C-nucleoside

“…The length of the C-C glycosyl bond (1.499 A) is in very good agreement with values found in other C-nucleosides (8)(9)(10)(11)(12)(13). It is interesting to note that C(4')-O (1') is just barely longer than C(1')-0(11) instead of by 0.03-0.05 A.…”

The crystal structure of formycin hydrobromide monohydrate

“…Both the groups are linked through a carboncarbon single bond in place of the nitrogen-carbon glycosyl bond in the usual nucleosides. This unusual feature of the attachment of the sugar moiety to the base has also been found in some natural products, such as pseudouridine (Rohrer & Sundaralingam, 1970), showdomycin (Tsukuda & Koyama, 1970) and pyrazomycin (Jones &Chaney, 1972). We shall discuss the structure in comparison with the published data for formycin monohydrate, adenosine and its analogues.…”

“Slim” Nucleosides and Nucleotides. I. Synthetic, Structural and Biophysical Investigations of Showdomycins

“…Single-crystal X-ray diffraction studies of showdomycin (33) have shown that it adopts a peri-syn conformation in the solid state wherein the 5'-0H is hydrogen bonded to the carbonyl group at position 2 as shown below:…”