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Amyloid fibril formation is associated with various amyloidoses, including neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Despite the numerous studies on the inhibition of amyloid formation, the prevention and treatment of a majority of amyloid-related disorders are still challenging. In this study, we investigated the effects of various plant extracts on amyloid formation of α-synuclein. We found that the extracts from Eucalyptus gunniiare able to inhibit amyloid formation, and to disaggregate preformed fibrils, in vitro. The extract itself did not lead to cell damage. In the extract, miquelianin, which is a glycosylated form of quercetin and has been detected in the plasma and the brain, was identified and assessed to have a moderate inhibitory activity, compared to the effects of ellagic acid and quercetin, which are strong inhibitors for amyloid formation. The properties of miquelianin provide insights into the mechanisms controlling the assembly of α-synuclein in the brain.Graphical AbstractInhibitory effect of Eucalyptus gunniiextract on α-synuclein amyloid fibrils.

Pyrrolysine-tRNAPylcomplex is produced by pyrrolysyl-tRNA synthetase (PylRS). In this study, we investigated the substrate specificity of Desulfitobacterium hafniencePylRS. PylRS incorporated various L-lysine derivatives into tRNAPylin vitro. In addition, the PylRS/tRNAPylpair introduced these lysine derivatives into the recombinant protein by the Escherichia coliexpression system, indicating that this PylRS/tRNAPylpair can be used in protein engineering technology.

A MUC1 type of glycopeptide was synthesized by the 9-fluorenylmethoxycarbonyl (Fmoc) solid-phase peptide synthesis (SPPS) protocol using benzyl and benzylidene-protected β-D-Gal-(1→3)-β-D-GalNAc-Ser/Thr (TF-β: a stereoisomer of the Thomsen-Friedenreich antigen). The synthetic glycopeptide was released from the resin with reagent K, and the resulting benzylated glycopeptide was deprotected under conditions of low-acidity trifluoromethanesulfonic acid (TfOH). The glycopeptide carrying duplicate non-natural O-glycans was dominant in the products, but was accompanied by a considerable amount of the glycopeptide missing one of the O-glycans. In contrast, the native α-glycoside was relatively stable under the acidic debenzylation conditions as shown by a parallel experiment with the glycopeptide involving α-D-GalNAc-Ser/Thr linkage. Enzymatic glycosylation with CMP-NeuAc was successful with both natural and non-natural O-glycans of the synthetic glycopeptide.

The benzyl-protected disaccharide building blocks of core 8 O-glycan (15a/15b) for glycopeptide were stereoselectively synthesized by two glycosidation reactions with the glycosyl fluoride method. The building blocks were utilized in the solid-phase synthesis of a glycopeptide carrying two O-glycans with the consensus sequence of the tandem-repeat domain of MUC5AC. The synthetic glycopeptide was detached from the resin with reagent K, and subsequent debenzylation under conditions of low-acidity TfOH afforded glycopeptide 2. The synthetic sample will be used as a suitable standard in studies of the physicochemical or immunochemical characterization of mucin glycoforms.

An unnatural α-D-mannopyranose-linked chitobiosyl dolichyl pyrophosphate, a stereoisomer of the N-glycan biosynthesis intermediate, was synthesized. The protected trisaccharide, α-D-Man-(1→4)-β-D-GlcNAc-(1→4)-D-GlcNAc, carrying a 4-methylbenzoyl group was prepared for the convenience of a TLC analysis. 1-O-Phosphorylation, condensation with dolichyl phosphate, and subsequent deprotection afforded the title compound.

A core-class 2 tetrasaccharide-linked serine was synthesized in a convergent manner. The coupling reaction of disaccharide glycosyl donor 3 and acceptor 4 stereoselectively afforded tetrasaccharide 15, which was converted to glycosyl fluoride 20. Glycosylation of Fmoc serine allyl ester 5 with 20 produced α- and β-glycosides in 40% and 33% yields, respectively. α-Isomer 21 was converted into 1, a useful building block for the solid-phase synthesis of glycopeptides. On the other hand, 21 was N-deprotected and condensed with hydrophobic cholestanol through a succinyl spacer. The same compound was alternatively synthesized by coupling 20 and 28. Functional group manipulation and hydrogenation afforded core 2 tetrasaccharide-cholestanol conjugate 2.