A Novel Class of Defensive Compounds in Harvestmen: Hydroxy-γ-Lactones from the Phalangiid Egaenus convexus

When threatened, the harvestman Egaenus convexus (Opiliones: Phalangiidae) ejects a secretion against offenders. The secretion originates from large prosomal scent glands and is mainly composed of two isomers of 4-hydroxy-5-octyl-4,5-dihydro-3 H -furan-2-one ( 1 ), a β-hydroxy-γ-lactone. The compounds were characterized by GC-MS of their microreaction derivatives, HRMS, and NMR. After the synthesis of all four possible stereoisomers of 1 , followed by their separation by chiral-phase GC, the absolute configurations of the lactones in the Egaenus secretion was found to be (4 S ,5 R )- 1 (90%) and (4 S ,5 S )- 1 (10%). Hydroxy-γ-lactones represent a new class of exocrine defense compounds in harvestmen.