New Macrocyclic Bis-5-alkylresorcinols from Nutshells of Macadamia with Antifungal Activity against Soft Rot

Macadamia nutshell, an abundant agro-industrial byproduct, afforded 5 new and 25 known compounds in our investigation, in which macyclophanes A-C feature rare 5-alkylresorcinol-derived 6/18/6 macrocyclic framework reported for the first time. Moreover, new compound macyclophane A showed the most potent bioactivity against Rhizopus stolonifer, with a MIC value of 16 μg/mL, and was associated with disruption of plasma membrane integrity and leakage of cellular contents. Furthermore, macyclophane A suppressed R. stolonifer infection of strawberry effectively, comparable to myclobutanil. The findings suggest that macadamia nutshells might be a promising sustainable natural source for postharvest disease control.