Ersitat Ramon Llull, Through Augusta 390, E-08017 Barcelona, Spain; [email protected] (J.M.O.); [email protected] (R.P.d.l.B.); [email protected] (R.E.-T.); [email protected] (J.T.) Correspondence: [email protected]; Tel.: 34-660-921-Abstract: Naphthyridines, also called diazanaphthalenes, are a group of heterocyclic compounds that incorporate six isomeric bicyclic systems containing two pyridine rings. 1,6-Naphthyridines are a single on the members of such a family capable of offering ligands for several receptors in the physique. Amongst such structures, 1,6-naphthyridin-2(1H)-ones (7) are a subfamily that incorporates greater than 17,000 compounds (having a single or double bond involving C3 and C4) included in greater than 1000 references (the majority of them patents). This assessment will cover the analysis of your diversity of the substituents present at positions N1, C3, C4, C5, C7, and C8 of 1,6-naphthyridin-2(1H)-ones, the synthetic strategies made use of for their synthesis (both beginning from a preformed pyridine or pyridone ring), and also the biomedical applications of such compounds.Citation: Oliveras, J.M.; Puig de la Bellacasa, R.; Estrada-Tejedor, R.; Teixid J.; Borrell, J.I. 1,6-Naphthyridin-2(1H)-ones: Synthesis and Biomedical Applications. Pharmaceuticals 2021, 14, 1029. https://doi.org/10.3390/ ph14101029 Academic Editors: Thierry Besson and Pascal Marchand Received: 12 September 2021 Accepted: four October 2021 Published: 9 OctoberKeywords: 1,6-naphthyridin-2(1H)-one; substitution pattern; synthesis; biological activity1. Introduction In the starting of any analysis project aimed in the improvement of new prospective drug candidates for the treatment of a specific disease, 1 from the most important choices to become taken will be the selection of the central molecular structure (scaffold) on which to introduce the substituents required to interact together with the corresponding biological receptor. Such scaffolds might be selected based around the natural ligands in the receptor, the synthetic background on the study group, or, frequently, applying the so-called privileged heterocyclic structures, a notion introduced by Evans inside the late 1980s [1,2]. Such privileged structures are usually heterocyclic compounds for instance quinoline, benzimidazole, pyrazole, indole, piperazine, and other individuals, which might be present in numerous drugs created all through the history of medicinal chemistry. A Moveltipril Purity & Documentation further instance of such privileged heterocycles are pyrido[2,3-d]pyrimidine structures and, extra specifically, pyrido[2,3d]pyrimidin-7(8H)-ones [3] that have Bafilomycin C1 Biological Activity permitted our group to describe compounds with nM activities as breakpoint-cluster-region protein (BCR) kinase inhibitors for B lymphoid malignancies [4], discoidin domain-containing receptor 2 (DDR2) inhibitors for treatment of lung cancer [5], such as hepatitis C virus (HCV) inhibitors [6], and also other biological activities. Comparable structures are naphthyridines, also called pyridopyridines and benzodiacins, a group of diazanaphthalene compounds composed of six isomeric heterocyclic systems containing two pyridine rings. They will be divided into two small groups: the 1,Xnaphthyridines (X = 5, 6, 7, 8) along with the two,X-naphthyridines (X = 6, 7) (Figure 1) [7]. Since the synthesis by Reissert in 1893 with the initially naphthyridine, who proposed the offered name, we had to wait till 1927 when the unsubstituted 1,5-naphthyridine (1) and 1, eight naphthyridine (four) were synthesized. Finally, the household was completed together with the synthesis in 1958 of 1,6-(2).