Synthesis of 5′-methylenearisteromycin and its 2-fluoro derivative with potent antimalarial activity due to inhibition of the parasite S-adenosylhomocysteine hydrolase1

Synthesis and antiplasmodial activity of purine-based C-nucleoside analogues

A series of homologous C-nucleoside mimics have been synthesized via an efficient and facile synthetic protocol involving the conjugate addition of purine to sugar derived olefinic ester in good yields. The synthesized compounds were evaluated for their antiplasmodial activity in vitro against both the CQ-sensitive and resistant strains of P. falciparum. Interestingly, all the synthesized nucleoside analogs exhibited an IC₅₀ of <5 μM, while compounds 22a, 23a, and 23b showed promising antiplasmodial activity with an IC₅₀ of 1.61, 0.88, and 1.01 μM against the CQ-sensitive Pf3D7 strain and 1.14, 1.01, and 2.57 μM against the CQ-resistant PfK1 strain, respectively.

Diastereoselective Synthesis of 6″-(Z)- and 6″-(E)-Fluoro Analogues of Anti-hepatitis B Virus Agent Entecavir and Its Evaluation of the Activity and Toxicity Profile of the Diastereomers

A method for the diastereoselective synthesis of 6″-(Z)- and 6″-(E)-fluorinated analogues of the anti-HBV agent entecavir has been developed. Construction of the methylenecyclopentane skeleton of the target molecules has been accomplished by radical-mediated 5-exo-dig cyclization of the selenides 6 and 15 having the phenylsulfanylethynyl structure as a radical accepting moiety. In the radical reaction of the TBS-protected precursor 6, (Z)-anti-12 was formed as a major product. On the other hand, TIPS-protected 15 gave (E)-anti-12. The sulfur-extrusive stannylation of anti-12 furnished a mixture of geometric isomers of the respective vinylstannane, whereas benzoyl-protected 17 underwent the stannylation in the manner of retention of configuration. Following XeF2-mediated fluorination, introduction of the purine base and deoxygenation of the resulting carbocyclic guanosine gave the target (E)- and (Z)-3 after deprotection. Evaluation of the anti-HBV activity of 3 revealed that fluorine-substitution at the 6″-position of entecavir gave rise to a reduction in the cytotoxicity in HepG2 cells with retention of the antiviral activity.

A linchpin carbacyclization approach for the synthesis of carbanucleosides

A convenient synthesis of carbanucleosides, with both enantiomers equally accessible, is reported. The key step is a tandem linchpin cyclization process to give access to substituted carbafuranose derivatives having the correct relative stereochemistry for subsequent nucleobase introduction with inversion of configuration at C1. This was illustrated by the synthesis of 2',3'-dideoxycarbathymidine via a convergent nucleobase introduction and of 2',3'-dideoxy-6'-hydroxycarbauridine via a linear nucleobase introduction. Both methods relied on Mitsunobu chemistry, and the first example of the Mukaiyama modification of the Mitsunobu reaction involving nucleobases as nucleophiles is reported.

Nucleosides and nucleotides. 232. Synthesis of 2'-C-methyl-4'-thiocytidine: unexpected anomerization of the 2'-keto-4'-thionucleoside precursor

The synthesis of 2'-C-methyl-4'-thiocytidine (16) is described. Since the 2'-keto-4'-thiocytidine derivative 2beta unexpectedly isomerized to 2alpha and the methylation of 2beta proceeded predominantly from the less hindered alpha-face to give 7, the desired product 16 was synthesized via the Pummerer reaction of the sulfoxide 14 and N4-benzoylcytosine.