Definition: In this task, you're given a paragraph from the research paper and your task is to generate a suitable title for the research paper based on the given paper. Under 100 words is a good title length.
Input: Several hitherto unknown (E)-but-2-enyl nucleoside phosphonoamidate analogs (ANPs) were prepared directed with nitrogen reagents by cross-metathesis in water-under ultrasound irradiation. Two diastereoisomers were formally identified by X-ray diffraction. These compounds were evaluated against a large spectrum of DNA and RNA viruses. Among them, the phosphonoamidate thymine analogue 19 emerged as the best prodrug against varicella-zoster virus (VZV) with EC 50 values of 0.33 and 0.39 mM for wild-type and thymidine kinase deficient strains, respectively, and a selectivity index !200 mM. This breakthrough approach paves the way for new purine and pyrimidine (E)-but-2-enyl phosphonoamidate analogs. Abbreviations: VZV, varicella zoster virus; VV, vaccinia virus; HSV, herpes simplex virus; VSV, vesicular stomatitis virus; DNA, deoxyribonucleic acid; RNA, ribonucleic acid; CC50, compound concentration affording 50% inhibition of cell growth; EC50, compound concentration affording 50% inhibition of the viral cytopathicity; MCC, minimum cytotoxic concentration required to afford a microscopically detectable alteration of cell morphology; ACN, acetonitrile; DCM, dichloromethane.

Highly convergent synthesis and antiviral activity of (E)-but-2-enyl nucleoside phosphonoamidates