Discovery and Synthesis of Heterocyclic Carboxamide Derivatives as Potent Anti-norovirus Agents

Abstract

There is an urgent need for structurally novel anti-norovirus agents. In this study, we describe the synthesis, anti-norovirus activity, and structure-activity relationship (SAR) of a series of heterocyclic carboxamide derivatives. Heterocyclic carboxamide 1 (50% effective concentration (EC 50 ) 37 µM) was identified by our screening campaign using the cytopathic effect reduction assay. Initial SAR studies suggested the importance of halogen substituents on the heterocyclic scaffold and identified 3,5-di-boromo-thiophene derivative 2j (EC 50 24 µM) and 4,6-di-fluoro-benzothiazole derivative 3j (EC 50 5.6 µM) as more potent inhibitors than 1. Moreover, their hybrid compound, 3,5-di-bromo-thiophen-4,6-di-fluoro-benzothiazole 4b, showed the most potent anti-norovirus activity with a EC 50 value of 0.53 µM (70-fold more potent than 1). Further investigation suggested that 4b might inhibit intracellular viral replication or the late stage of viral infection.Key words norovirus; heterocyclic carboxamide; antiviral activity; murine norovirus Human norovirus causes acute nonbacterial gastroenteritis. Although the gastroenteritis symptoms are generally self-limiting, the elderly, infants, and immunocompromised individuals have a higher risk of mortality. Moreover, norovirus has a low infectious dose and spreads very easily from infected persons, contaminated food, water, or a contaminated environment. 1)Noroviruses are single-stranded, positive-sense RNA viruses that belong to the family Caliciviridae and genus Norovirus, and species Norwalk virus. The norovirus genome contains three open reading frames (ORFs): ORF1, ORF2, and ORF3. ORF1 encodes six or seven nonstructural proteins, including RNA-dependent RNA polymerase (RdRp) and 3C-like cysteine protease (3CLpro), responsible for viral replication. ORF2 and ORF3 encode the major and minor structural proteins, respectively. 1)Establishment of an efficient cell culture system for human norovirus is still challenging.2,3) However, murine norovirus (MNV) can replicate efficiently in the murine macrophage cell line RAW264.7. MNV belongs to the genus Norovirus and shares common biological and molecular properties with human norovirus.4,5) Therefore, it is frequently used for identifying antiviral compounds based on the cell culture assay. [6][7][8][9][10][11][12] Several anti-norovirus agents have been reported that target viral attachment/entry, viral protein translation, or viral replication. 7,8) The RdRp inhibitor used as an anti-hepatitis C virus agent 2′-C-methylcytidine (2′-CMC) 9,10) and anti-influenza agent favipiravir 11) also have anti-MNV activity, and the broad spectrum 3CLpro inhibitor, dipeptidyl inhibitor GC376 also inhibits MNV protease activity in vitro.12) Currently, there are no vaccines or drugs for clinical use, and there is an urgent need for new anti-norovirus compounds.We describe here the discovery and synthesis of anti-norovirus thienyl benzothiazolyl carboxamide compounds bearing multiple halogen substituents, and discuss their structure-activity ...

Antiviral effect of theaflavins against caliciviruses

“…5-Bromo-N-(6-fluorobenzo[d]thiazol-2-yl)thiophene-2-carboxamide (BFTC) was synthesized as described previously. 8 For further experiments, theaflavin (TF1), theaflavin-3-O-gallate (TF2A), theaflavin-3′-O-gallate (TF2B) and theaflavin-3, 3′-O, O-digallate (TF3) were purchased from Nagara Science (Gifu, Japan). Tea extracts containing 40% theaflavins and containing 90% theaflavins (obtained by removing caffeine and catechins from the tea extract containing 40% theaflavins) were purchased from Yaizu Suisankagaku Industry (Shizuoka, Japan).…”

“…Further structural optimization of BFTC resulted in identification of a 70-fold more potent derivative as previously reported. 8 PoSaV-induced CPE was specifically inhibited by EGCG hydrate, abamectin (a mixture of avermectin B1a and B1b) and avermectin B1a (Table 1). EGCG is the most abundant green tea catechin and shows many physiological activities, including antioxidant, antifungal, antibacterial, antiviral, anti-obesity and anti-inflammatory effects.…”

“…Whereas, another hit BFTC (Table 1) inhibits intracellular MNV replication or the late stages of MNV infection. 8 Our screening system, therefore, may be useful to discover various types of antiviral compounds. Four theaflavins (TF1, 2A, 2B and 3) and their mixtures showed more potent antiviral activity than tannic acid, which has been reported as an anti-FCV agent.…”

A Rapid Microwave Induced Synthesis of Isonicotinamide Derivatives and their Antifungal Activity

“…HE chemistry of carboxamide derivatives with various structural moieties have attracted much attention owing to their different biological properties: antimicrobial, [1][2][3][4][5][6] antifungal, [7][8][9][10] anti-inflammatory, [11] analgesic, [12,13] antitumoral, [14][15][16][17][18] antihypertensive, [19,20] anticonvulsant, [21,22] and antiviral [23] in the recent two decades. More than 255 of known drugs have a carboxamide group in its structure.…”

“…The bioassay results have shown that some of them exhibited excellent antifungal activities. [23][24][25][26][27][28] It has been proven that pyridine carboxamide group display fungicidal activity by disrupting the mitochondrial tricarboxylic acid cycle (TCA) through inhibition of the succinate dehydrogenase (SDH) enzyme, also called succinate ubiquinone oxidoreductase (SQR). [29] The most of fungicides are heterocyclic toxic substances which selectively destroy fungal phytopatho-gens ( Figure 1).…”