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

Interplay of Modified Sialic Acid Inhibitors and the Human Parainfluenza Virus 1 Hemagglutinin-Neuraminidase Active Site

In the search for effective antivirals against Paramyxoviridae, the dynamics of human parainfluenza virus type 1 hemagglutinin-neuraminidase (hPIV1-HN) inhibition offers a promising perspective. This study focuses on the potential of C5- and C4-modified 2,3-unsaturated sialic acid (DANA) inhibitors and highlights their interaction with the hPIV1-HN enzyme. We show that a strategic substitution, replacing the C5 isopropyl group in BCX 2798 with a trifluoroacetyl function, increases inhibitory potency 3- to 4-fold. At the same time, we explore the special properties of the catalytic site of hPIV1-HN, which harbors only small substituents and favors a C4 sulfonylamido function over a carbonyl function, in contrast to the C4 pocket of Newcastle disease virus hemagglutinin-neuraminidase (NDV-HN). Based on these findings, we present a newly identified potent inhibitor that has the preferred C5 trifluoroacetamido and C4 trifluorosulfonylamide groups. The results of this study pave the way for a deeper understanding of the C4 and C5 binding pockets of hPIV1-HN and promote the development of new, more selective inhibitors.

Analysis of the intramolecular 1,7-lactone of N-acetylneuraminic acid using HPLC-MS: relationship between detection and stability

A subclass of the sialic acid family consists of intramolecular lactones that may function as key indicators of physiological and pathological states. However, the existence of these compounds in free form is highly improbable, since they are unlikely to exist in an aqueous solution due to their lability. Current analytical method used to detect them in biological fluids has not recognized their reactivity in solution and is prone to misidentification. However, recent advances in synthetic methods for 1,7-lactones have allowed the preparation of these sialic acid derivatives as authentic reference standards. We report here the development of a new HPLC-MS method for the simultaneous detection of the 1,7-lactone of N-acetylneuraminic acid, its γ-lactone derivative, and N-acetylneuraminic acid that overcomes the limitations of the previous analytical procedure for their identification.

Design, Synthesis, and Antiviral Evaluation of Sialic Acid Derivatives as Inhibitors of Newcastle Disease Virus Hemagglutinin-Neuraminidase: A Translational Study on Human Parainfluenza Viruses

Global infections with viruses belonging to the Paramyxoviridae, such as Newcastle disease virus (NDV) or human parainfluenza viruses (hPIVs), pose a serious threat to animal and human health. NDV-HN and hPIVs-HN (HN hemagglutinin-neuraminidase) share a high degree of similarity in catalytic site structures; therefore, the development of an efficient experimental NDV host model (chicken) may be informative for evaluating the efficacy of hPIVs-HN inhibitors. As part of the broad research in pursuit of this goal and as an extension of our published work on antiviral drug development, we report here the biological results obtained with some newly synthesized C4- and C5-substituted 2,3-unsaturated sialic acid derivatives against NDV. All developed compounds showed high neuraminidase inhibitory activity (IC₅₀ 0.03-13 μM). Four molecules (9, 10, 23, 24) confirmed their high in vitro inhibitory activity, which caused a significant reduction of NDV infection in Vero cells, accompanied by very low toxicity.

Small-Molecules as Chemiluminescent Probes to Detect Lipase Activity

The set-up of highly sensitive detection tools to evaluate lipase activity remains a central goal in different fields. In this context, we proposed new chemiluminescent 1,2-dioxetane luminophores, sharing an octanoyl triggerable group, to monitor lipase activity. We herein report the synthesis and both the evaluation of their luminescence emission profile and their enzyme-substrate specificity, generated by three different commercial lipases (Candida cylindracea, Pseudomonas fluorescens, and Mucor miehei) and one esterase (porcine liver esterase, PLE, as a literature control). Remarkably, the present study confirmed the applicability of these 1,2-dioxetane luminophores as (i) highly efficient, broad-range, chemiluminescent probes for the detection and the enzymatic activity evaluation of lipases and as (ii) promising candidates for the future development of both flash- and glow-type luminescence assays.

Intramolecular Lactones of Sialic Acids

The so-called "sialo-chemical-biology" has become an attractive research area, as an increasing number of natural products containing a sialic acid moiety have been shown to play important roles in biological, pathological, and immunological processes. The intramolecular lactones of sialic acids are a subclass from this crucial family that could have central functions in the discrimination of physiological and pathological conditions. In this review, we report an in-depth analysis of the synthetic achievements in the preparation of the intramolecular lactones of sialic acids (1,4-, 1,7- and γ-lactones), in their free and/or protected form. In particular, recent advances in the synthesis of the 1,7-lactones have allowed the preparation of key sialic acid derivatives. These compounds could be used as authentic reference standards for their correct determination in biological samples, thus overcoming some of the limitations of the previous analytical procedures.

2β-3,4-Unsaturated sialic acid derivatives: Synthesis optimization, and biological evaluation as Newcastle disease virus hemagglutinin-neuraminidase inhibitors

The optimization of the synthetic protocol to obtain the 3,4-unsaturated sialic acid derivatives, through the fine-tuning of both the Ferrier glycosylation conditions and the subsequent hydrolysis work-up, is herein reported. The accomplishment of the desired β-anomers and some selected α-ones, in pure form, led us to evaluate their specific inhibitory activity towards NDV-HN and human sialidase NEU3. Importantly, the resulting data allowed the identification, for the first time, of three active 3,4-unsaturated sialic acid analogs, showing IC₅₀ values against NDV-HN in the micromolar range.

The acidic hydrolysis of N-acetylneuraminic 4,5-oxazoline allows a direct functionalization of the C5 position of Neu5Ac2en (DANA)

The Neu5Ac 4,5-oxazoline ring-opening allows the direct generation of a free C5-amino group key to synthesize antiviral drugs.

Lactonization Method To Assign the Anomeric Configuration of the 3,4-Unsaturated Congeners of N-Acetylneuraminic Acid

Assigning the correct configuration at C2 in sialosides is a standing problem because of the absence of an anomeric hydrogen. All different empirical rules that have been proposed over the years lack general applicability. In particular, the correct configuration of several 3,4-unsaturated derivatives of N-acetylneuraminic acid (Neu5Ac), which have been recently shown to be novel sialidase/neuraminidase inhibitors, could only be tentatively assigned by similarity with the reported 3,4-unsaturated 2O-methyl sialosides. In this work, we overcome this problem as we devised a rapid synthetic method to unequivocally resolve the anomeric configuration of the 3,4-unsaturated Neu5Ac derivatives through the synthesis of the corresponding unreported unsaturated 1,7-lactones. Moreover, we discovered a diagnostic ¹³C nuclear magnetic resonance signal that allows the formulation of a new empirical rule for the direct assignment of the C2 stereochemistry of these molecules, even when only one of the two C2 epimers is available.