Chemical Investigation of Nest Materials from the Solitary Bees Hylaeus relegatus and Hylaeus nubilosus

Solitary bees are known to prepare nests for their larvae in order to provide protection from bacteria, fungi and the elements. The protective and biodegradable nature of the nest material has resulted in physical properties relevant to the field of durable water repellants, a source of persistent organic pollutants.

Polyester nest materials produced by the Colletes genus of solitary bees were known to be derived from macrocyclic lactone monomers produced in their Dufour’s gland. Similar macrocyclic lactones were also found in the Dufour’s gland of three Australasian members of the Hylaeus genus of solitary bees. Developing an effective synthetic route to these macrocyclic lactones was thus the focus of the research prior to obtaining and analyzing authentic Hylaeus nest material.

Synthetic efforts focused on generating a novel route towards macrocyclic lactones contained within the Dufour’s gland of the investigated solitary bee species, suspected to be the primary monomers of the nest material polymer. (16E)-22-Docos-16-enolide 2 and 22-docosanolide 3 were synthesized from 16-hexadecanolide 1 in 4/5 steps respectively - a shorter route than reported alternatives, from commercially available starting materials, outlined in Scheme 1. The strategy involved a ring enlargement beginning with a commercially available C16 lactone,transesterification of the starting lactone, oxidation of the α- and ω-hydroxyl groups, a Wittig olefination to transform the terminal aldehydes into alkenes, and ring-closing metathesis assisted by the Grubbs-II catalyst to give larger macrocyclic lactones. Polymerization of the macrocyclic lactones (16E)-22-docos-16-enolide 2 and 22-docosanolide 3 yielded poly((16E)-22- Docos-16-enolide) 4 and poly(22-docosanolide) 5.

Utility of the devised synthetic route to macrocyclic lactones also led to the synthesis of novel compounds (17E)-19-methyloxacycloicos-17-en-2-one 6 and (1R,21R,19E)-3-oxabicyclo[19.2.2]pentacos-19-en-4-one 7.

Analysis of authentic Hylaeus nest materials was undertaken once nest material samples were obtained. Infrared spectroscopy suggested nest materials of Hylaeus nubilosus and Hylaeus relegatus bees did not contain a polyester material, but rather, a proteinaceous silk-like component.

Following this discovery, the highlight of this research was conducting primary amino acid analysis by pre-column derivatization via the ortho-phthalaldehyde/thiol reaction with sub-mg quantities of nest material followed by HPLC with fluorescence detection. This information aided future research involving the Hylaeus nubilosus genomic information, which coded for the production of the nest material.