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

Abstract

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.

Concise Stereoselective Synthesis of β-Hydroxy-γ-lactones: (4R,5R)-4-Hydroxy-γ-decalactone from the Japanese Orange Fly and Enantiomers of Arachnid Harvestmen Isolates

“…4 Similarly, the spectroscopic data for ent-3 was in excellent agreement to that of the natural isolate and the synthesized compound in the literature. 6 The specific rotation value of ent-3, [α] D 25 −33 (c 0.5, CHCl 3 ), matches well with that of the synthesized compound, [α] D −32.3 (c 0.13, CHCl 3 ), in the literature. 6 However, this could not be compared with that of the natural isolate, as it is not provided in the isolation report.…”

“…6 The specific rotation value of ent-3, [α] D 25 −33 (c 0.5, CHCl 3 ), matches well with that of the synthesized compound, [α] D −32.3 (c 0.13, CHCl 3 ), in the literature. 6 However, this could not be compared with that of the natural isolate, as it is not provided in the isolation report. The absolute configuration for the natural isolate 3 was assigned by Raspotnig and co-workers 6 by comparison of the chiral HPLC profiles, and it was not based on specific rotations.…”

“…Analysis of the crude product indicated 7a/7b = 1:9 mixture (by 1 H NMR). The residue was purified by silica gel column chromatography using petroleum ether/EtOAc (7:3) as eluent to afford 7b (0.224 g, 85%, based on recovered 7a) as a colorless oil: [α] D 25 −27 (c 1.0, CHCl 3 ); IR (CHCl 3 ): ν max 3437,2926,1773,1645,1414,1358,1269,1181,1100,1060,989,936,879,719, 592 cm −1 ; 1 H NMR (500 MHz, CDCl 3 ): δ 5.88−5.82 (m, 1H), 5.41 (d, J = 17.2 Hz, 1H), 5.30 (d,J = 10.7 Hz,1H),1H),1H),2.79 (dd,J = 17.8,6.2 Hz, 1H), 2.6 (brs, 1H), 2.49 (dd, J = 17.8, 3.3 Hz, 1H); 13 C NMR (125 MHz, CDCl 3 ): δ 175. 6, 132.7, 118.2, 87.4, 71.7, 36.6; HRMS (ESI-TOF) m/z 129.0555 [M + H] + (calcd for C 6 H 9 O 3 , 129.0552).…”

“…The syn-diastereomers (4-epi-3 and its antipode) were prepared by the SAD reaction to enable the assignment of the absolute configuration to the naturally isolated lactones by HPLC analysis. 6 It can be concluded from these synthetic studies that the syn-lactones are easily accessible but the isomeric anti-lactones are not. With our interest in the synthesis of γ-butyrolactones and the recent use of the chiral pool material D-glucono-δ-lactone in efficient one-pot conversion to γ-vinyl-β-hydroxy-γ-lactone and thereby synthesis of various natural products, 11,12 we envisaged a concise synthesis of both diastereomers of the 4-hydroxy-γ-butyrolactones.…”

“…4 The anti-lactone 3 has been synthesized from commercially available (R)-benzyl glycidyl ether (5) in six steps, requiring two protecting groups and addition of the expensive Evans-auxiliary (Figure 2C). 6 The use of opposite enantiomer resulted in the synthesis of ent-3. The syn-diastereomers (4-epi-3 and its antipode) were prepared by the SAD reaction to enable the assignment of the absolute configuration to the naturally isolated lactones by HPLC analysis.…”