Recent Advances in Marine Natural Products as Antibacterial Agents: Structural Elucidation, Pharmacological Activities, and Structure-Activity Relationship (2020–2024)

Marine natural products (MNPs) have emerged as a vital source of novel antibiotic lead compounds due to their unique chemical architectures and remarkable antibacterial activities. This review systematically summarizes recent advances (2020–2024) in antibacterial marine-derived analogues, with a focus on their structural elucidation, pharmacological properties, and structure–activity relationships (SAR). The discussed compounds are primarily isolated from sponges, corals, tunicates, and marine microorganisms, and structurally categorized into alkaloids, polyketides, peptides, polysaccharides, and macrolides. These molecules frequently exhibit complex polycyclic frameworks, halogen substitutions (e.g., bromine and chlorine), and glycosylation patterns, which critically govern their antibacterial potency and selectivity. Studies reveal that most compounds display significant inhibitory effects against clinically resistant strains such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci, with minimum inhibitory concentrations of several lead compounds reaching nanomolar levels. SAR analyses elucidate the pivotal roles of structural elements, including halogenation patterns, alkyl chain length, glycosylation degree, and stereochemistry, in modulating antibacterial efficacy. This review aims to provide a theoretical foundation and resource reference for the development of innovative antibacterial agents, while also outlining future challenges and research directions in the field of marine-derived antibacterial drug discovery.