Synthesis of 4-Guanidino-7-Modified-Neu5Ac2en Derivatives and Their Biological Activities as Influenza Sialidase Inhibitors

Abstract

Substitution of 7–OH with small hydrophobic groups on zanamivir resulted in the retention of low nanomolar inhibitory activities against not only influenza A virus sialidase but also influenza A virus in cell culture. These compounds were prepared by treatment of the corresponding 7–substituted sialic acids derived from 4–modified N–acetyl–D–mannosamine (ManNAc) using enzyme–catalyzed aldol condensation. A series of 7–alkyl ether derivatives related to Zanamivir were synthesized using direct alkylation of the C–7 alcohol of sialic acid. An alkyl ether moiety of less than 12 carbons in length showed low nanomolar inhibitory activity against influenza A virus sialidase. A series of ester prodrugs of compound (10b) was synthesized and their efficacy was evaluated in an influenza infected mouse model by intranasal administration. The compound (25c: CS–8958), octanoyl ester prodrug of the C–9 alcohol of compound (10b), was found to be much longer acting than Zanamivir. Polyvalent sialidase inhibitors bearing 4–guanidino–Neu5Ac2en analogues on the polyglutamic acid backbone, via a spacer of alkyl ether at the C–7 position, were synthesized. The multivalent conjugates (32) and (33) showed enhancement of antiviral activity against influenza A virus and more potent efficacy in vivo re-lative to monomeric sialidase inhibitors.