Pyrrolo[3,4-c]pyridine is one of the six structural isomers of the bicyclic ring system containing a pyrrole moiety fused to a pyridine nucleus. The broad spectrum of pharmacological properties of pyrrolo[3,4-c]pyridine derivatives is the main reason for developing new compounds containing this scaffold. This review presents studies on the biological activity of pyrrolo[3,4-c]pyridines that have been reported in the scientific literature. Most of these derivatives have been studied as analgesic and sedative agents. Biological investigations have shown that pyrrolo[3,4-c]pyridines can be used to treat diseases of the nervous and immune systems. Their antidiabetic, antimycobacterial, antiviral, and antitumor activities also have been found.

Marine and terrestrial environments are rich sources of various bioactive substances, which have been used by humans since prehistoric times. Nowadays, due to advances in chemical sciences, new substances are still discovered, and their chemical structures and biological properties are constantly explored. Drugs obtained from natural sources are used commonly in medicine, particularly in cancer and infectious diseases treatment. Naphthyridines, isolated mainly from marine organisms and terrestrial plants, represent prominent examples of naturally derived agents. They are a class of heterocyclic compounds containing a fused system of two pyridine rings, possessing six isomers depending on the nitrogen atom’s location. In this review, biological activity of naphthyridines obtained from various natural sources was summarized. According to previous studies, the naphthyridine alkaloids displayed multiple activities, i.a., antiinfectious, anticancer, neurological, psychotropic, affecting cardiovascular system, and immune response. Their wide range of activity makes them a fascinating object of research with prospects for use in therapeutic purposes.

2,7-Naphthyridine is one of the six structural isomers of pyridopyridine. Biological investigations have shown that these compounds have a broad spectrum of activity. They have been found to have antitumor, antimicrobial, analgesic and anticonvulsant effects. The broad spectrum of biological activity of 2,7-naphthyridine derivatives is the main reason for the preparation of new compounds containing this scaffold. This review aims to present various methods of obtaining 2,7-naphthyridine analogs. Compounds containing a 2,7-naphthyridine moiety can be synthesized from a variety of substrates and may be classified into four main categories: those derived from acyclic compounds, from quinoline derivatives, from pyridine derivatives, and from other compounds. Most of them were obtained by the cyclocondensation or intramolecular cyclization of pyridine derivatives. Cyclocondensations of non-cyclic substrates also produced 2,7-naphthyridine derivatives. Tricyclic benzo[2,7]naphthyridines were prepared from quinolines. The 2,7-naphthyridine scaffold has also been synthesized by the rearrangement of pyrrolo[3,4-c]pyridines, pyrano[3,4-c]pyridines or thiopyrano[3,4-c]pyridines.

To combat the problem of the increasing drug resistance of microorganisms, it is necessary to constantly search for new medicinal substances that will demonstrate more effective mechanisms of action with a limited number of side effects. Naphthyridines are N-heterocyclic compounds containing a fused system of two pyridine rings, occurring in the form of six structural isomers with different positions of nitrogen atoms, which exhibit a wide spectrum of pharmacological activity, in particular antimicrobial properties. This review presents most of the literature data about the synthetic and natural naphthyridine derivatives that have been reported to possess antimicrobial activity.

Imide derivatives constitute an interesting group of compounds exhibiting broad biological activity. Structures containing the imide moiety [–CO–N(R)–CO–] occur in both natural and synthetic compounds. Several drugs containing an imide moiety are in therapeutic use. In this review, we present the structures and describe the effects of cyclic imide derivatives, which primarily exhibit anti-inflammatory activity. Some of the presented derivatives have been studied in detail, and their additional analgesic, anticancer, and antibacterial effects have been described. The relative neuroprotective properties of imide derivatives are also described, as are reports of their effect on lowering cholesterol and triglyceride levels. In this review, we discuss monocyclic imide derivatives (succinimide, glutarimide, maleimide, and hydantoin), bicyclic derivatives (e.g., phthalimide), and polycyclic imides.