Pyridin-4-on-Nueleosid⁺: Stabilisierung der Struktur im Kristall und in wäßriger Lösung / Pyridine-4-on Nucleoside: Stabilisation of the Structure in the Crystal and in Aqueous Solution

Abstract

<jats:title>Abstract</jats:title><jats:p> C10H13NO5 • H2O is monoclinic, space group P2i with a = 773.7 pm, b = 814.6 pm, c= 932.6 pm, β = 109.36° at 143 K, Z = 2. The crystal structure has been refined to R =0.031 with 1340 counter reflections. Features of this nucleoside include an orientation of the base at the glycosidic bond N(l)-C(l') in the anii-range (52.5°), a ribosyl moiety in the C(2')-endo(S) conformation and in contrast to many other nucleosides a trans arrange-ment at C(4')-C(5'). This unusual conformation is stabilized by a distinct H-bonding scheme including the water molecule and the oxygen of the adjacent pyridin-4-on ring system. NMR data indicate on the other side that in solution the conformation of the nucleoside is anti/g + similar to that of other pyrimidine nucleosides. The 5'-OH group replaces the water molecule in the crystal. The preferred anti position of the base cannot be explained by an interaction of H(2,6) of the base with the 5'-OH group or the C(4) oxygen. Both protons which couple with H(3,5) coalesce in a single sharp doublet. Water entropy seems to be the decisive factor for the stabilization of the anti/g+ conformation in aqueous solution.</jats:p>

The Pterocellins, Novel Bioactive Alkaloids from the Marine Bryozoan Pterocella vesiculosa

“…The C-6-O-1 bond length of 1.21 Å is significantly shorter than the C-9-O-2 length of 1.24 Å, suggesting the former is more . [11][12][13][14] Otherwise bond lengths and angles fall within usual ranges, with the main deviation of some angles arising from the strain of fusing five-and six-membered rings.…”

“…An examination of the individual bond lengths suggests that there is little delocalization of π-electron density across the middle ring since the C-5−C-6, C-6−C-7, and N-12−C-13 bonds are long and are all essentially single. The butyl-substituted pyridine ring is aromatic, but the electron density within the substituted pyridone ring is localized in short C-7−C-8 and C-10−C-11 bonds to give a dienone moiety (as in simpler 4-pyridone molecules). − Otherwise bond lengths and angles fall within usual ranges, with the main deviation of some angles arising from the strain of fusing five- and six-membered rings.

1 Structure of one independent molecule of pterocellin A ( 1 ) showing the numbering system.

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