Gemcitabine is a modified cytidine analog having two fluorine atoms at the 2′-position of the ribose ring. It has been proposed that gemcitabine inhibits RNR activity by producing a C3′• intermediate via direct H3′-atom abstraction followed by loss of HF to yield a C2′• with 3′-keto moiety. Direct detection of C3′• and C2′• during RNR inactivation by gemcitabine still remains elusive. To test the influence of 2′- substitution on radical site formation, electron spin resonance (ESR) studies are carried out on one-electron oxidized gemcitabine and other 2′-modified analogs, i.e., 2′-deoxy-2′-fluoro-2′-C-methylcytidine (MeFdC) and 2′-fluoro-2′-deoxycytidine (2′-FdC). ESR line components from two anisotropic β-2′-F-atom hyperfine couplings identify the C3′• formation in one-electron oxidized gemcitabine, but no further reaction to C2′• is found. One-electron oxidized 2′-FdC is unreactive toward C3′• or C2′• formation. In one-electron oxidized MeFdC, ESR studies show C2′• production presumably from a very unstable C3′• precursor. The experimentally observed hyperfine couplings for C2′• and C3′• match well with the theoretically predicted ones. C3′• to C2′• conversion in one-electron oxidized gemcitabine and MeFdC has theoretically been modeled by first considering the C3′• and H3O+ formation via H3′-proton deprotonation and the subsequent C2′• formation via HF loss induced by this proximate H3O+. Theoretical calculations show that in gemcitabine, C3′• to C2′• conversion in the presence of a proximate H3O+ has a barrier in agreement with the experimentally observed lack of C3′• to C2′• conversion. In contrast, in MeFdC, the loss of HF from C3′• in the presence of a proximate H3O+ is barrierless resulting in C2′• formation which agrees with the experimentally observed rapid C2′• formation.

Treatment of the protected and unprotected nucleosides with 1,3-dibromo-5,5- dimethylhydantoin in aprotic solvents such as CH2Cl2, CH3CN, or DMF effected smooth bromination of uridine and cytidine derivatives at C-5 of pyrimidine rings as well as adenosine and guanosine derivatives at C-8 of purine rings. Addition of Lewis acids such as trimethylsilyl trifluoromethanesulfonate enhanced efficiency of bromination.

Despite continuous efforts to control cariogenic dental biofilms, very few effective antimicrobial treatments exist. In this study, we characterized the activity of the novel synthetic cyclic lipopeptide 4 (CLP-4), derived from fusaricidin, against the cariogenic pathogen UA159. We determined CLP-4's MIC, minimum bactericidal concentration (MBC), and spontaneous resistance frequency, and we performed time-kill assays. Additionally, we assessed CLP-4's potential to inhibit biofilm formation and eradicate preformed biofilms. Our results demonstrate that CLP-4 has strong antibacterial activity and is a potent bactericidal agent with low spontaneous resistance frequency. At a low concentration of 5 μg/ml, CLP-4 completely inhibited UA159 biofilm formation, and at 50 μg/ml, it reduced the viability of established biofilms by>99.99%. We also assessed CLP-4's cytotoxicity and stability against proteolytic digestion. CLP-4 withstood trypsin or chymotrypsin digestion even after treatment for 24 h, and our toxicity studies showed that CLP-4 effective concentrations had negligible effects on hemolysis and the viability of human oral fibroblasts. In summary, our findings showed that CLP-4 is a potent antibacterial and antibiofilm agent with remarkable stability and low nonspecific cytotoxicity. Hence, CLP-4 is a promising novel antimicrobial peptide with potential for clinical application in the prevention and treatment of dental caries.

Treatment of toyocamycin or sangivamycin with 1,3-dibromo-5,5-dimethylhydantoin in MeOH (r.t./30 min) gave 8-bromotoyocamycin and 8-bromosangivamycin in good yields. Nucleophilic aromatic substitution of 8-bromotoyocamycin with sodium azide provided novel 8-azidotoyocamycin. Strain promoted click reactions of the latter with cyclooctynes resulted in the formation of the 1,2,3-triazole products. Iodine-mediated direct C8-H bond functionalization of tubercidin with benzotriazoles in the presence of tert-butyl hydroperoxide gave the corresponding 8-benzotriazolyltubercidin derivatives. The 8-(1,2,3-triazol-1-yl)-7-deazapurine derivatives showed moderate quantum yields and a large Stokes shifts of ~ 100 nm.

The 7-deazapurine nucleoside antibiotic tubercidin was converted into its 4-N-benzyl and 4-N-(4-nitrobenzyl) derivatives by alkylation at N3 followed by Dimroth rearrangement to the 4-N- isomer or by fluoro-diazotization followed by SNAr displacement of the 4-fluoro group by a benzylamine. The 4-N-(4-nitrobenzyl) derivatives of sangivamycin and toyocamycin antibiotics were prepared by the alkylation approach. Cross-membrane transport of labeled uridine by hENT1 was inhibited to a weaker extent by the 4-nitrobenzylated tubercidin and sangivamycin analogues than was observed with 6-N-(4-nitrobenzyl)adenosine. Type-specific inhibition of cancer cell proliferation was observed at μM concentrations with the 4-N-(4-nitrobenzyl) derivatives of sangivamycin and toyocamycin, and also with 4-N-benzyltubercidin. Treatment of 2′,3′,5′-O-acetyladenosine with aryl isocyanates gave the 6-ureido derivatives but none of them exhibited inhibitory activity against cancer cell proliferation or hENT1.