Synthesis and chemical characterization of several perfluorinated sialic acid glycals and evaluation of their in vitro antiviral activity against Newcastle disease virus

Abstract

Newcastle Disease Virus (NDV), belonging to the Paramyxoviridae family, causes a serious infectious disease in birds, resulting in severe losses in the poultry industry every year. Haemagglutinin neuraminidase glycoprotein (HN) has been recognized as a key protein in the viral infection mechanism, and its inhibition represents an attractive target for the development of new drugs based on sialic acid glycals, with the 2-deoxy-2,3-didehydro-d--acetylneuraminic acid (Neu5Ac2en) as their backbone. Herein we report the synthesis of several Neu5Ac2en glycals and of their perfluorinated C-5 modified derivatives, including their respective stereoisomers at C-4, together with evaluation of their antiviral activity. While all synthesized compounds were found to be active HN inhibitors in the micromolar range, we found that their potency was influenced by the chain-length of the C-5 perfluorinated acetamido functionality. Thus, the binding modes of the inhibitors were also investigated by performing a docking study. Moreover, the perfluorinated glycals were found to be more active than the corresponding normal C-5 acylic derivatives. Finally, cell-cell fusion assays on NDV infected cells revealed that the addition of a newly synthesized C-4α heptafluorobutyryl derivative almost completely inhibited NDV-induced syncytium formation.

Potent Inhibitors against Newcastle Disease Virus Hemagglutinin‐Neuraminidase

“…Moreover, while we observed an increase of the IC 50 value, moving from the trifluoroacetamido 3 b to the corresponding N ‐pentafluoroacetamido 3 c derivative (7.43 μ m ), the inhibitory activity was restored when we further elongated the chain to the N ‐heptafluorobutyramide 3 d . Interestingly, the trend that we identified in series 2, resembled the one that we previously reported for the C4 hydroxy analogues . However, the derivatives 3 a – d showed an improvement in the inhibitory potency over the natural C4 hydroxy analogues.…”

“…The synthesized compounds were tested against NDV‐HN by performing a NI assay . Interestingly, the inhibitors 2 a and 3 a showed IC 50 values in a nanomolar range (0.178 and 0.543 μ m , respectively), remarkably lower than the highest‐potency inhibitor reported to date, FANA (2.42 μ m , Figure ) . In particular, the presence of a p ‐toluenesulfonyl amido group at C4 in compound 2 a resulted in a remarkable improvement in potency, with a IC 50 value 14‐fold lower than FANA.…”

“…On these premises, as a part of our involvement in sialidase and sialoconjugate research, we developed a series of new NDV‐HN inhibitors starting from the DANA framework. In our multidisciplinary approach we took into account that DANA analogues with a) bulky C4 substituents have been reported to possess higher inhibitory activity against hPIVs‐HN,–, and b) C5 perfluorinated chains have been shown in our previous study to possess additional interactions with the catalytic site . Using both in silico docking simulations and in vitro biological activity studies, we evaluated several synthetic C4 modified DANA derivatives, including the corresponding analogues with a C5 perfluorinated chain (Figure ).…”

“…However, considering that some azido derivatives, such as BCX‐2798 1 b , have been reported among the most promising inhibitors against hPIVs, we also planned to synthesize the free azido compound 3 a . Additionally, we designed the synthesis of some unreported inhibitors, 2 b – d and 3 b – d , by combining the new selected C4 substituents ( p ‐toluenesulfonyl amido and azido) with the linear homologues perfluoracylamides at C5, from trifluoroacetic to heptafluorobutyric, that we previously reported . Moreover, we synthesized the pentanoyl and hexanoyl perfluorinated derivatives of DANA, 4 a , b , to investigate the effects of longer side chains at C5 (Scheme ).…”

“…The desired final compounds 4 a , b were easily obtained by acylation of known intermediate 5 and successive complete deprotection of the peracetylated compounds 6 a , b . Finally, compounds 4 a , b were tested for their capacity to block NDV‐HN by performing a neuraminidase inhibition (NI) assay on in‐toto purified NDV, showing IC 50 values significantly higher (43 μ m and 151 μ m , respectively; Figure ) than those of inferior perfluorinated homologs …”