Research Article: 7-Iodo-5-aza-7-deazaguanine ribonucleoside: crystal structure, physical properties, base-pair stability and functionalization

Date Published: May 01, 2020

Publisher: International Union of Crystallography

Author(s): Dasharath Kondhare, Simone Budow-Busse, Constantin Daniliuc, Frank Seela.


7-Iodo-5-aza-7-de­aza­guanosine represents a base-modified nucleoside with an entirely different recognition pattern as the parent purine com­pound. It shows an anti conformation at the glycosylic bond and an N conformation (O4′-endo) for the ribose moiety. Packing is controlled by hydrogen bonds and by a 7-iodo contact to 2′-oxygen of the ribose moiety.

Partial Text

The specific recognition of com­plementary nucleobases in the DNA coding system is based on the combination of purine and pyrimidine bases (Watson & Crick, 1953 ▸). Adenine pairs with thymine and guanine with cytosine. Nevertheless, an alternative coding system entirely com­posed of purines (‘all-purine’ DNA) was suggested by Wächtershäuser (1988 ▸). In this, purines glycosyl­ated at nitro­gen-9 (adenine and guanine) base pair with purines glycosyl­ated at nitro­gen-3 (motif I xanthine and motif II isoguanine, see Fig. 1 ▸; purine numbering is used throughout this article). The resulting purine–purine base pairs are isoelectronic and isogeometric to standard purine–pyrimidine Watson–Crick pairs. However, purines glycosyl­ated at nitro­gen-3 are unstable and difficult to handle (Leonard, 2020 ▸).

The single-crystal X-ray structure of 7-iodo-5-aza-7-de­aza­guanosine (1) was determined and the geometric parameters of this RNA constituent were analyzed. This includes an anti conformation of the 5-aza-7-de­aza­guanine base, an N conformation (O4′-endo) of the ribose moiety and an anti­periplanar orientation of the 5′-hy­droxy group.




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