Recent Advances in the Synthesis of the Carbocyclic Nucleosides as Potential Antiviral Agents

Compared with 4′-oxonucleosides, there have been far fewer systematic structure-activity relationship studies on carbocyclic nucleosides as antiviral and antitumour agents. This is mainly because of the synthetic problems in preparing the carbasugars. However, the recent discovery of the ring-closing metathesis (RCM) (a powerful tool for the preparation of 5-membered carbasugar via C-C bond formation) has made it possible to synthesize the key carbasugars to a preparative scale. This review summarizes the asymmetric syntheses of carbasugars and carbocyclic nucleosides, using an RCM reaction as a key step. Furthermore, the review includes valuable information for designing and synthesizing novel carbocyclic nucleosides.

X-ray crystal structure and binding mode analysis of human S-adenosylhomocysteine hydrolase complexed with novel mechanism-based inhibitors, haloneplanocin A analogues

The X-ray crystal structure of human S-adenosylhomocysteine (AdoHcy) hydrolase was first determined as a tetrameric form bound with the novel mechanism-based inhibitor fluoroneplanocin A (4b). The crystallized enzyme complex showed the closed conformation and turned out to be the intermediate of mechanism-based inhibition. It confirmed that the cofactor depletion by 3'-oxidation of fluoroneplanocin A contributes to the enzyme inhibition along with the irreversible covalent modification of AdoHcy hydrolase. In addition, a series of haloneplanocin A analogues (4b-e and 5b-e) were designed and synthesized to characterize the binding role and reactivity of the halogen substituents and the 4'-CH(2)OH group. The biological evaluation and molecular modeling studies identified the key pharmacophores and structural requirements for the inhibitor binding of AdoHcy hydrolase. The inhibitory activity was decreased as the size of the halogen atom increased and/or if the 4'-CH(2)OH group was absent. These results could be utilized to design new therapeutic agents operating via AdoHcy hydrolase inhibition.

Synthesis of fluoroneplanocin A

Fluoroneplanocin A, designed as a potent mechanism-based irreversible inhibitor of S-adenosylhomocysteine hydrolase (SAH), is synthesized from D-ribose via a key D-cyclopentenone intermediate. This intermediate is synthesized using a stereoselective Grignard reaction, a ring-closing metathesis (RCM) reaction, and oxidative rearrangement as key steps.

Synthesis and antitumor activity of fluorocyclopentenyl-pyrimidines

Synthesis of fluorocyclopentenyl pyrimidine nucleosides 6-9 was enantiopurely accomplished employing oxidative rearrangement, RCM reaction and electrophilic fluorination starting from d-ribose. Cytosine analog 8 was found to exhibit significant anticancer activity in various human tumor cell lines.