Synthesis and Biological Evaluation of Structurally Varied 5′-/6′-Isonucleosides and Theobromine-Containing N-Isonucleosidyl Derivatives

Abstract

Isonucleosides are rather stable regioisomeric analogs of nucleosides with broad therapeutic potential. We have previously demonstrated the ability of 5′ and 6′-isonucleosides to inhibit the activity of acetylcholinesterase, a major target for Alzheimer’s disease therapy. Continuing with our research on this topic, we report herein on the synthesis and biological evaluation of a variety of novel terminal isonucleosides and theobromine isonucleotide analogs. Xylofuranose-based purine or uracil 5′-isonucleosides and xylofuranos-5′-yl or glucos-6′-yl theobromine derivatives were accessed via Mitsunobu coupling between partially protected xylofuranose or glucofuranose derivatives with a nucleobase using conventional or microwave-assisted heating conditions. Theobromine-containing N-isonucleosidyl sulfonamide and phosphoramidate derivatives were synthesized from isonucleosidyl acetate precursors. The most active compounds in the cholinesterase inhibition assays were a glucopyranose-based theobromine isonucleosidyl acetate, acting as a dual inhibitor of acetylcholinesterase (AChE, Ki = 3.1 µM) and butyrylcholinesterase (BChE, Ki = 5.4 µM), and a 2-O,4-O-bis-xylofuranos-5′-yl uracil derivative, which displayed moderate inhibition of AChE (Ki = 17.5 µM). Docking studies revealed that the active molecules are positioned at the gorge entrance and at the active site of AChE. None of the compounds revealed cytoxic activity to cancer cells as well as to non-malignant mouse fibroblasts.

Synthesis of Triazole‐Containing Furanosyl Nucleoside Analogues and Their Phosphate, Phosphoramidate or Phoshonate Derivatives as Potential Sugar Diphosphate or Nucleotide Mimetics

“…On the other hand, the methylenic protons in the 1,5-disubstituted triazole 34 gave signals corresponding to the parts A and B of an ABMX system (ABM = 1 H, X = 31 P), showing the geminal coupling ( 2 J a,b = 15.7) in addition to the individual 3 J couplings with the phosphorous atom (J H-a,P = 9.5, J H-b,P = 12.1) and with the phosphonoamino proton (J H-a,NH = 9.5, J H-b,NH = 5.4). Similarly to that observed in the 13 C NMR spectra of their phosphate counterparts 24-27, the triazole quaternary carbon atoms of the (triazolyl)methyl phosphoramidates 32-34 resonated as doublets with J C,P = ca. 6 Hz.…”

“…Thus, the 5-azido 3-Obenzyl and 3-O-dodecyl xylofuranose derivatives (18, 19) were synthesized by tosylation of the partially protected xylofuranoses 16 [13e] and 17 [8c] and subsequent tosylate substitution with sodium azide (Scheme 3). Thermal cycloaddition between the 3-O-benzylated precursor 18 and propargyl alcohol in refluxing toluene afforded the 4-hydroxymethyl-1-xylofuranosyl triazole 20 and the 1,5-regioisomer 21 in 46 % and 36 % yields, respectively, which were clearly identified based on the 13 C NMR chemical shifts of their triazole carbon signals. While in the 1,4-disubstituted triazole 20, the signals for C-4 and C-5 appeared at 147.5 ppm and 123.0 ppm, respectively, in the 1,5dissubstituted counterpart 21, C-4 and C-5 resonated at 133.3 ppm and 137.3 ppm, respectively.…”

“…While in the 1,4-disubstituted triazole 20, the signals for C-4 and C-5 appeared at 147.5 ppm and 123.0 ppm, respectively, in the 1,5dissubstituted counterpart 21, C-4 and C-5 resonated at 133.3 ppm and 137.3 ppm, respectively. These characteristic 13 C NMR chemical shift differences between 1,4-and 1,5-disubstituted triazoles were considered for the structural assignment of the different regioisomers of the further triazole derivatives described below.…”

“…13 Hz) and the individual couplings with the phosphorous atom (J H-a,P = 9.2 Hz and J Hb,P = 8.4 Hz). Moreover, the 13 C NMR signals for the triazole quaternary carbon atom atoms (C-4 or C-5) of the (triazolyl)methyl phosphates 24-27 appeared as doublets due to coupling with the phosphorous atom (J C,P = ca.7.5 Hz).…”

“…These molecules include acyclic nucleos(t)ides, [5] carbocyclic derivatives [6] or other sugar heteroanalogue-containing nucleosides, [7] nucleosides comprising uncommon glycosyl units, [8] C-nucleosides, [9] nucleoside alkyl/aryl phosphodi/triesters, [10] phosphoramidates or H-or Cphosphonates. [10,11] Other biological effects of therapeutic relevance have been reported for nucleos(t)ides and analogues, including antibiotic properties, acting as inhibitors of crucial microbial cell processes, [12] or ability to inhibit cholinesterases, [13] which are important therapeutic targets for Alzheimer's disease symptomatic treatment. Among the described cholinesterase inhibitors are our previously reported 5'/6'-isonucleosides, [13c-f] which comprise a nucleobase or an analogous nitrogeneous heteroaromatic moiety N-linked to a sugar moiety at C-5 or C-6, and D-glucofuranuronamide-based N-glycosyl triazoles.…”