Hallesiins

Hallesiins are a class of natural products primarily isolated from the marine sponge *Haliclona* species, particularly those belonging to the genus *Haliclona* (formerly classified under *Halichondria*). These compounds belong to the broader category of macrolides, characterized by their large lactone ring structures and diverse biological activities.

The first member of this class, **halliolide A**, was discovered in 1992 from a sponge collected near the coast of Japan. Since then, several related compounds, such as hallisiolides B–E and halisulfins, have been identified. These metabolites often exhibit potent antimicrobial, cytotoxic, and anti-inflammatory properties, making them subjects of interest in pharmaceutical research.

Structurally, hallesiins feature polyketide origins, incorporating various functional groups like hydroxyls, ketones, and unsaturated bonds. Their biosynthesis involves complex enzymatic pathways, often mediated by modular polyketide synthases. Due to their limited availability from natural sources, synthetic and semi-synthetic approaches have been explored to study their mechanisms of action and potential therapeutic applications.

Research on hallesiins has focused on their ability to inhibit bacterial growth, particularly against multidrug-resistant pathogens, and their potential as anticancer agents. However, their complex structures and low natural abundance have hindered widespread clinical development. Ongoing studies aim to optimize their production and elucidate their precise biological targets to overcome these challenges.