Viruses belonging to the Flaviviridae family primarily spread through arthropod vectors, and are the major causes of illness and death around the globe. The Flaviviridae family consists of 3 genera which include the Flavivirus genus (type species, yellow fever virus) as the largest genus, the Hepacivirus (type species, hepatitis C virus) and the Pestivirus (type species, bovine virus diarrhea). The flaviviruses (Flavivirus genus) are small RNA viruses transmitted by mosquitoes and ticks that take over host cell machinery in order to propagate. However, hepaciviruses and pestiviruses are not antropod-borne. Despite the extensive research and public health concern associated with flavivirus diseases, to date, there is no specific treatment available for any flavivirus infections, though commercially available vaccines for yellow fever, Japanese encephalitis and tick-born encephalitis exist. Due to the global threat of viral pandemics, there is an urgent need for new drugs. In many countries, patients with severe cases of flavivirus infections are treated only by supportive care, which includes intravenous fluids, hospitalization, respiratory support, and prevention of secondary infections. This review discusses the strategies used towards the discovery of antiviral drugs, focusing on rational drug design against Dengue virus (DENV), West Nile virus (WNV), Japanese encephalitis virus (JEV), Yellow Fever virus (YFV) and Hepatitis C virus (HCV). Only modified peptidic, nonpeptidic, natural compounds and fragment-based inhibitors (typically of mass less than 300 Da) against structural and non-structural proteins are discussed.

Background: The Diels-Alder reaction has been widely utilised in the syntheses of biologically important natural products over the years and continues to greatly impact modern synthetic methodology. Recent discovery of chiral organocatalysts, auxiliaries and ligands in organic synthesis has paved the way for their application in Diels-Alder chemistry with the goal to improve efficiency as well as stereochemistry. Objective: The review focuses on asymmetric syntheses of flavonoid Diels-Alder natural products that utilize chiral ligand-Lewis acid complexes through various illustrative examples. Conclusion: It is clear from the review that a significant amount of research has been done investigating various types of catalysts and chiral ligand-Lewis acid complexes for the enantioselective synthesis of flavonoid Diels-Alder natural products. The results have demonstrated improved yield and enantioselectivity. Much emphasis has been placed on the synthesis but important mechanistic work aimed at understanding the enantioselectivity has also been discussed.

This chapter describes the biosynthesis and biomimetic synthesis of naturally occurring flavonoid Diels-Alder adducts found either from the family Moraceae or Zingiberaceae. The main topics addressed are biosynthetic studies by employing Morus alba L. cell cultures through feeding experiments of various exogenous substrates and putative precursors, as well as a various biomimetic approach for the chemical syntheses of flavonoid Diels-Alder natural products.

In the title mol­ecule, C12H10N2O4, the pyridine and benzene rings are almost orthogonal [dihedral angle = 86.69 (11)°], with the pyridine N atom directed towards the centre of the benzene ring. The –NO2 [O—N—C—C = −26.1 (3)°] and –OMe [C—O—C—C = 166.5 (2)°] substituents are not coplanar with their respective aromatic rings. In the crystal, supra­molecular layers in the ab plane are formed via C—H⋯π inter­actions involving methyl H atoms and the pyridine and benzene rings. Short N—O⋯π contacts (where the π-system is derived from the pyridine ring) occur between layers in the c-axis direction.

A nearly orthogonal relationship is found for the ring systems in the title compound, C15H10N2O3, with the dihedral angle between the rings being 86.13 (11)°. The nitro group is approximately coplanar with the pyridine ring to which it is connected [the O—N—C—C torsion angle = −1.8 (4)°]. This coplanarity allows for the close approach of these residues in the crystal structure enabling the formation of N—O⋯π(pyridine) inter­actions [3.547 (4) Å]. Further consolidation of the crystal packing is afforded by weak π–π inter­actions [centroid–centroid distances = 3.9576 (16) and 3.9822 (16) Å].