Chemically Engineered Sulfates of Lasiodiplodan: Antioxidant, Antimicrobial, and Antirespiratory Syncytial Virus (RSV) Activities

β-Glucans are carbohydrate macromolecules with significant clinical and biotechnological applications, whose biological properties are enhanced through chemical modifications, such as sulfation. This study aimed to chemically engineer sulfated derivatives of the (1→6)-β-d-glucan lasiodiplodan and to evaluate how different degrees of sulfation influence its antioxidant, antimicrobial, and antiviral activities. The chemically engineered sulfated derivatives LAS-S1 (DS 0.11) and LAS-S2 (DS 0.51) were synthesized using the sulfating agent chlorosulfonic acid, with different solvents: N,N-dimethylformamide (solvent/stabilizer) and pyridine (proton-neutralizing agent). Sulfation improved the solubility and enhanced the biological activities of both derivatives. LAS-S2 demonstrated better antimicrobial and antiviral activity than LAS-S1. Sulfation was shown to contribute to ·OH and H2O2 scavenging activity, with a dose-dependent effect related to both the concentration of the sulfated compound and its degree of sulfation. The fungistatic and bacteriostatic effects were demonstrated against Escherichia coli, Listeria monocytogenes, Salmonella enterica Typhimurium, Candida albicans, and Candida tropicalis. LAS-S2 exhibited potent inhibition of respiratory syncytial virus (RSV) in vitro, with a high selectivity index (>724.63), and interfered with multiple stages of viral replication. These findings highlight sulfation as an effective strategy to enhance the biological functions of lasiodiplodan. LAS-S2 emerges as a safe (noncytotoxic) and promising candidate for biotechnological and pharmaceutical applications, including novel antimicrobial and antiviral treatments. Future studies should focus on elucidating structure–activity relationships, optimizing sulfation patterns, and evaluating the in vivo efficacy and pharmacological properties of sulfated lasiodiplodan derivatives.