The structure of 8-thioxoadenosine monohydrate

Abstract

The structure of 8-thioxoadenosine monohydrate, C10HtaNsOaS. H20 , has been determined. The crystals are monoclinic, space group P2~, with a = 8.758 (1), b = 6.717(1), c = 11.462 (2) A, /] = 95.22(1) °, Z = 2. The structure was refined to R = 0.048. The conformation about C (4')-C (5') is gauche-trans, and the puckering of the ribose is C(2')-endo-C(3')-exo. The molecule exhibits a syn conformation about the glycosyl bond in spite of the absence of an intramolecular O(5')-H... N(3) hydrogen bond. The bases are stacked into columns, overlapping mainly at the S substituents of adjacent molecules. All the donor atoms are involved in hydrogen bonds, while the S atom acts as a hydrogen-bond acceptor.

8-Chloroguanosine: solid-state and solution conformations and their biological implications

“…Hence, although the van der Waals radius of chlorine is smaller than that of bromine (1.75 A as compared to 1.85 A), the chlorine atom is sufficiently bulky to force the syn-anti equilibrium toward the syn form, also reflected by the behavior in solution (see below). The same effect has been observed in numerous crystal structures of 8-iodo-, 8-bromo-, and 8-methylpurine nucleosides as well as in 8-thioxoadenosine (Mizuno et al, 1980). Thus far, only nitrogen substituents (-N3, -NHR) have been shown to be small enough to favor the anti conformation (Ambady & Kartha, 1975;Neidle et al, 1979).…”

“…It would be desirable to examine the influence of other substituents, e.g., the highly electron-withdrawing 8-F with a van der Waals radius of 1.47 A (Bondi, 1964), which would offer considerably less steric hindrance to adoption of the anti conformation [the synthesis of 8-fluoroadenosine has been reported by Secrist et al (1982)]. This, in turn, might be compared with the behavior of an analogue such as the 8-thione (Mizuno et al, 1980), in which the ==S substituent has a van der Waals radius of 1.75 A (Bondi, 1964), similar to that of a chlorine atom, and an electronegativity slightly less than that of chlorine (Huheey, 1965). Apart from the foregoing, the enzyme system of Huang et al ( 1983) provides a convenient procedure for the preparation of 8-substituted purine nucleosides, not easily accessible by chemical routes.…”

Synthesis and Triplex Formation of Oligonucleotides Containing 8-Thioxodeoxyadenosine

“…These results also showed that 8-oxoadenine base could bind to the G-C base pair, whereas the unmodified A could not. The orientation of the glycosyl bond of 8-oxoadenosine is known to be syn . It is also suggested that this modified base has a syn conformation in its deoxyribonucleoside counterpart .…”