Heteroatoms can be found in a number of naturally occurring substances, active pharmaceutical ingredients, as well as excipients, substituting isosteric/bioisosteric carbon atoms. Many oxygen- and sulfur-containing heterocycles such as oxirane, thiirane, oxetane, dioxetane, oxolane, dioxolane, dioxane, trioxane, (benzo)furan, (benzo)thiophene, (benzo)pyran, benzodioxine, xanthene, and chromene can be considered as privileged scaffolds due to statistics describing as more than 85% of all biologically-active chemical entities endowed with a heterocycle in their structure. This topic reflects the pivotal role of heterocycles in modern drug design and development and their utilization in the scaffold-hopping strategy.

Oxygen- and sulfur-containing compounds were shown to exhibit a very wide range of biological activities mimicking natural compounds or endogenous metabolites. A large chemical diversity can be obtained by different and innovative synthetic methodologies to expand/explore the available drug-like chemical space and to obtain robust Structure-Activity Relationships (SARs) within each scaffold. Moreover, the presence of heterocycles could provide the improvement of solubility, lipophilicity, polarity, and hydrogen bonding ability toward biologically active agents, as well as the optimization of their ADME/Tox properties.

This Special Issue encourages original research and review articles on the most recent findings devoted to the topics listed below.

Potential topics include but are not limited to the following:

• Innovative synthesis of new chemical entities
• Derivatives from natural compounds with improved characteristics
• Biomaterials for biomedical and industrial applications
• Drug design to discover new biologically active agents
• In-silico investigations of the heterocycles
• Biological screening of heterocyclic compounds
• Hyphenated analytical techniques to characterize heterocycles
• Isolation from natural matrices of new oxygen- and sulfur-containing heterocyclic derivatives