Synthesis and Biological Evaluation of 2- and 7-Substituted 9-Deazaadenosine Analogues

Abstract

A series of 2-halogen and 7-alkyl substituted analogues of 9-deazaadenosine and 2'-deoxy-9-deazaadenosine was synthesized by new efficient methodology involving transformation of corresponding 9-deazaguanosine and 2'-deoxyguanosine, which in turn were synthesized by direct C-glycosylation of 1-benzyl-9-deazaguanine with 1-O-acetyl-2,3,5-tri-O-benzoyl-D-ribofuranose and methyl 2-deoxy-3,5-di-O-(p-toluoyl)-D-ribofuranoside, respectively. Deoxychlorination of C6 and diazotization/chloroor fluoro-dediazoniation of the sugar-protected 9-deazaguanosine, followed by selective ammonolysis at C6 and deprotection of the sugar moiety, gave 2-chloro- and 2-fluoro-9-deazaadenosine (6 and 9). Substitution of the 7-position of the dihalogen-intermediate with alkyl groups, followed by ammonolysis and deprotection, provided 2-chloro-7-alkyl-9-deazaadenosines (13a-e) and 2-fluoro-7-benzyl-9-deazaadenosine (13f). Catalytic hydrogenation of 13a-e gave 7-alkyl-9-deazaadenosines 14a-e. Similarly, 2-chloro-2'-deoxy-9-deazaadenosine (21), 2-chloro-2'-deoxy-7-methyl-9-deazaadenosine (25), 2'-deoxy-9-deazaadenosine (22), and 2'-deoxy-7-methyl-9-deazaadenosine (26) were prepared from sugar-protected 2'-deoxy-9-deazaguanosine. Among these compounds, 7-benzyl-9-deazaadenosine (14b) showed the most potent cytotoxic activity, with IC50 values of 0.07, 0.1, 0.2 and 1.5 microM, while both 7-methyl-9-deazaadenosine (14a) and 2-fluoro-9-deazaadenosine (9) also demonstrated significant cytotoxic activity with IC50 values of 0.4, 0.7, 0.3, and 1.5 microM, and 1.5, 0.9, 0.3, and 5 microM against L 1210 leukemia, P388 leukemia, CCRF-CEM lymphoblastic leukemia, and B16F10 melanoma cells, respectively.

Synthesis of 2′-Deoxy-9-deaza Nucleosides Using Heck Methodology

“…Klein et al first reported the synthesis of 9-deaza nucleosides by constructing the base at the anomeric carbon, resulting in the formation of epimers (2:1 β/α) and thereby lowering the yield of the desired β-product. − Subsequently, Pankiewicz and Sartorelli reported an approach using Friedel–Crafts conditions. , This route, however, also suffered similar issues and only provided the desired β-anomer in 21–25% yields as well as the α-anomer (9%) . As a result, an alternative was sought that would be stereospecific and higher yielding.…”

“…In the course of our efforts to introduce base modifications to nucleosides − for use in studies of modified DNA, a series of 2′-deoxy-9-deaza nucleosides were envisioned wherein the nucleobase is connected to the 2′-deoxyribofuranosyl moiety via a carbon–carbon bond, rendering them C - nucleosides. − In addition to imparting resistance to hydrolytic and enzymatic cleavage resulting from the more stable carbon–carbon glycosidic bond, ,, this change also results in altering H-bond accepting N7 to NH, an H-bond donor, for 2′-deoxy-9-deaza nucleosides such as 1 and 2 (Figure ). This allows these compounds to engage in alternative hydrogen-bonding patterns such as Hoogsteen base pairing, which may find use in complex oligonucleotide structures or in the investigation of polymerases. − Similarly, Hamm et al have evaluated alternate hydrogen-bonding patterns for 2′-deoxy-9-deazaguanosine to study the promutagenic characteristics of 8-oxo-2′-deoxyguanosine …”

Synthesis of a 3′‐Deoxy‐C‐Nucleoside Phosphonate Bearing 9‐Deazaadenine as Base Moiety

“…Notably, such C–C bond leads to a higher stability against both hydrolytic and enzymatic cleavage. A variety of C‐nucleoside analogues have been synthesized that contain 9‐deazaadenine and modified sugar rings; among these, the most successful example is BCX4430 or Immucilin A (Figure ), which has been described as a potential candidate for the treatment of filovirus infections [Ebola virus (EBOV) and Marburg virus (MARV)] . Additional modifications include the phosphoramidate prodrug GS‐5734 or remdesivir (Figure ), which is currently undergoing clinical development as EBOV inhibitor …”

The Synthesis of 6-Deazaformycin A

“…5 The high toxicity associated with the formycins has restricted their use for clinical development, but on the other hand has stimulated interest on the synthesis of structural analogues and their study from both chemical and biological points of view. A considerable number of base-modified analogues has been prepared and tested, including 5-chloro, 6 5-fluoro, 7 5-aminoformycin A, 7 5,7-disubstituted deazaformycin A, 8 and 2-or 3deoxyformycin A. 8 Some triazolo-C-nucleosides related to formycin A have been also prepared and have demonstrated significant cytotoxicity against L1210 and WIL2 leukemia cells in culture.…”

“…A considerable number of base-modified analogues has been prepared and tested, including 5-chloro, 6 5-fluoro, 7 5-aminoformycin A, 7 5,7-disubstituted deazaformycin A, 8 and 2-or 3deoxyformycin A. 8 Some triazolo-C-nucleosides related to formycin A have been also prepared and have demonstrated significant cytotoxicity against L1210 and WIL2 leukemia cells in culture. 9 During the last few years we have been involved in the study of the deazaformycins, which can provide useful informations on the importance of the heteroatoms present on the formycin scaffold, concerning the ability of these molecules to behave as antimetabolites and to possess cytotoxic activity thereof.…”