Structure of a zwitterionic O-polysaccharide from Photorhabdus temperata subsp. cinerea 3240

Scalable Synthesis of Versatile Rare Deoxyamino Sugar Building Blocks from d-Glucosamine

We report the syntheses of 1,3,4-tri-O-acetyl-2-amino-2,6-dideoxy-β-d-glucopyranose and allyl 2-amino-2,6-dideoxy-β-d-glucopyranoside from d-glucosamine hydrochloride. The potential of these two versatile scaffolds as key intermediates to a diversity of orthogonally protected rare deoxyamino hexopyranosides is exemplified in the context of fucosamine, quinovosamine, and bacillosamine. The critical C-6 deoxygenation step to 2,6-dideoxy aminosugars is performed at an early stage on a precursor featuring an imine moiety or a trifluoroacetamide moiety in place of the 2-amino group, respectively. Robustness and scalability are demonstrated for a combination of protecting groups and incremental chemical modifications that sheds light on the promise of the yet unreported allyl 2,6-dideoxy-2-N-trifluoroacetyl-β-d-glucopyranoside when addressing the feasibility of synthetic zwitterionic oligosaccharides. In particular, allyl 3-O-acetyl-4-azido-2,4,6-trideoxy-2-trifluoroacetamido-β-d-galactopyranoside, an advanced 2-acetamido-4-amino-2,4,6-trideoxy-d-galactopyranose building block, was achieved on the 30 g scale from 1,3,4,6-tetra-O-acetyl-β-d-glucosamine hydrochloride in 50% yield and nine steps, albeit only two chromatography purifications.

Total Synthesis of the Phosphorylated Zwitterionic Trisaccharide Repeating Unit of Photorhabdus temperata cinerea 3240

Herein, we report the total synthesis of the phosphorylated zwitterionic trisaccharide repeating unit of Photorhabdus temperata subsp. cinerea 3240. The efficient route involves regio- and stereoselective assembly of trisaccharide with rare deoxyamino sugar AAT at the nonreducing end, late stage oxidation, and installation of a phosphate linker on the trisaccharide. The total synthesis was completed via a longest linear sequence of 24 steps in 6.5% overall yield.

Total Synthesis of the Photorhabdus temperata ssp. Cinereal 3240 Zwitterionic Trisaccharide Repeating Unit

Zwitterionic carbohydrate modifications, such as phosphoethanolamine (PEtN), govern host-pathogen interactions. Whereas it is recognized that these modifications stimulate the host immune system, the purpose of PEtN modification remains largely descriptive. As an enabling step toward studying this carbohydrate modification, we report a synthesis of the P. temperata zwitterionic trisaccharide repeating unit. The 32-step synthesis was enabled by H-phosphonate chemistry to install the PEtN arm on a poorly reactive and sterically hindered C4-alcohol.

An Entomopathogenic Nematode Extends Its Niche by Associating with Different Symbionts

Bacterial symbionts are increasingly recognised as mediators of ecologically important traits of their animal hosts, with acquisition of new traits possible by uptake of novel symbionts. The entomopathogenic nematode Heterorhabditis downesi associates with two bacterial symbionts, Photorhabdus temperata subsp. temperata and P. temperata subsp. cinerea. At one intensively studied coastal dune site, P. temperata subsp. cinerea is consistently more frequently isolated than P. temperata subsp. temperata in H. downesi recovered from under the bare sand/Ammophila arrenaria of the front dunes (where harsh conditions, including drought, prevail). This is not the case in the more permissive closed dune grassland further from the sea. No differences were detected in ITS1 (internal transcribed spacer) sequence between nematode lines carrying either of the two symbiont subspecies, nor did they differ in their ability to utilise insects from three orders. The two symbionts could be readily swapped between lines, and both were carried in equal numbers within infective juveniles. In laboratory experiments, we tested whether the symbionts differentially affected nematode survival in insect cadavers that were allowed to dry. We assessed numbers of nematode infective juveniles emerging from insects that had been infected with H. downesi carrying either symbiont subspecies and then allowed to desiccate for up to 62 days. In moist conditions, cadavers produced similar numbers of nematodes, irrespective of the symbiont subspecies present, while under desiccating conditions, P. temperata subsp. cinerea cadavers yielded more nematode progeny than P. temperata subsp. temperata cadavers. Desiccating cadavers with the same nematode isolates, carrying either one or the other symbiont subspecies, confirmed that the symbiont was responsible for differences in nematode survival. Moreover, cadavers harbouring P. temperata subsp. cinerea had a reduced rate of drying relative to cadavers harbouring P. temperata subsp. temperata. Our experiments support the hypothesis that H. downesi can extend its niche into harsher conditions by associating with P. temperata subsp. cinerea.