Synthesis of Isotopically Labelled Disparlure Enantiomers and Application to the Study of Enantiomer Discrimination in Gypsy Moth Pheromone‐Binding Proteins

Abstract

To study the binding mechanism of disparlure (7,8)‐epoxy‐2‐methyloctadecane enantiomers with pheromone‐binding proteins (PBPs) of the gypsy moth, oxygen‐17 or 18 and 5,5,6,6‐deuterium labelled disparlure enantiomers were prepared in an efficient, enantioselective route. Key steps involve the asymmetric α‐chlorination of dodecanal by SOMO catalysis and Mitsunobu inversion of a 1,2‐chlorohydrin. The pheromone, (+)‐disparlure (7R, 8S), was tested in two infested zones, demonstrating that it is very attractive towards male gypsy moths. Studies of the binding of (+)‐disparlure and its antipode to gypsy moth PBPs by 2H &17O NMR at 600 MHz are reported. Chemical shifts, spin‐lattice relaxation decay times (T1) and transverse relaxation decay times (T2) of deuterium atoms of disparlure enantiomers in 2H NMR show that the binding of disparlure enantiomers to PBP1 differs from binding to PBP2, as expected from their opposite binding preferences (PBP1 binds (–)‐disparlure, and PBP2 binds (+)‐disparlure more strongly). Models of the disparlure enantiomers bound to one internal binding site and two external binding sites of both PBPs were constructed. The observed chemical shift changes of deuterated ligand signals, from non‐bound to bound, T1 and T2 values are correlated with results from the simulations. Together these results suggest that the disparlure enantiomers adopt distinct conformations within the binding sites of the two PBPs and interact with residues that line the sites.

Design and Synthesis of Fluorophore-Tagged Disparlure Enantiomers to Study Pheromone Enantiomer Discrimination in the Pheromone-Binding Proteins from the Gypsy Moth, Lymantria dispar

“…Furthermore, the binding site residues that vary between LdisPBPs were found to be: Asn35, Ala73, Leu91, and Ala135 in LdisPBP1, whereas in LdisPBP2 these residues were substituted with Asp35, Thr73, Ile91 and Leu136 (Sanes and Plettner 2016). Our recent NMR and molecular docking studies have demonstrated that the disparlure enantiomers adopt different conformations and orientations in the binding pocket of LdisPBP1 and LdisPBP2 (Pinnelli et al 2019). In addition, the two PBPs differ in their ligand binding association and dissociation kinetics.…”

“…The enantiopure α-chloroaldehyde 8 could be prepared from aldehyde intermediate 10 via asymmetric α-chlorination. We used the same approach to prepare (+)-and (-)-disparlure enantiomers (Pinnelli et al 2019). The asymmetric -chlorination of an aldehyde was also used previously in the synthesis of the posticlure enantiomers, which have a trans epoxide moiety (Kang and Britton 2007).…”

Synthesis of disparlure and monachalure enantiomers from 2,3-butanediacetals

“…They include the use of naturally occurring chiral substrates, such as ʟ-glutamic acid [13], ʟ-tartaric acid [14][15][16], ᴅ-glucose [17], and sorbitol [18] as starting materials, as well as enantioselective reactions, such as the Sharpless epoxidation [19][20][21][22][23][24], asymmetric dihydroxylation [25,26], chloroallyloboronation [27], or iodolactonization [28]. Most recently a method using the asymmetric chlorination of dodecanal by LiCl in the presence of a chiral imidazolidinone catalyst has also been described [29]. However, many of these methods have some drawbacks -the most important one being the insufficient enantiomeric purity for biological and commercial applications [29].…”

“…Most recently a method using the asymmetric chlorination of dodecanal by LiCl in the presence of a chiral imidazolidinone catalyst has also been described [29]. However, many of these methods have some drawbacks -the most important one being the insufficient enantiomeric purity for biological and commercial applications [29]. (+)-Disparlure used in most commercial lures is prepared by the Sharpless epoxidation reaction, which gives the final product with ees not exceeding 95% [29], which is insufficient to be used as attractant for males of the Gypsy moth.…”

“…However, many of these methods have some drawbacks -the most important one being the insufficient enantiomeric purity for biological and commercial applications [29]. (+)-Disparlure used in most commercial lures is prepared by the Sharpless epoxidation reaction, which gives the final product with ees not exceeding 95% [29], which is insufficient to be used as attractant for males of the Gypsy moth. In one of these methods the diols 5 and 7 were used as precursors in the synthesis of the cisepoxides 1 and 3 (Scheme 1).…”