Asparagine-linked N-glycans on proteins have diverse structures, and their functions vary according to their structures. In recent years, it has become possible to obtain high quantities of N-glycans via isolation and chemical/enzymatic/chemoenzymatic synthesis. This has allowed for progress in the elucidation of N-glycan functions at the molecular level. Interaction analyses with lectins by glycan arrays or nuclear magnetic resonance (NMR) using various N-glycans have revealed the molecular basis for the recognition of complex structures of N-glycans. Preparation of proteins modified with homogeneous N-glycans revealed the influence of N-glycan modifications on protein functions. Furthermore, N-glycans have potential applications in drug development. This review discusses recent advances in the chemical biology of N-glycans.

The chemical synthesis of af ully sialylated tetraantennary N-glycan has been achieved for the first time by using the diacetyl strategy,i nw hich NHAc is protected as NAc 2 to improve reactivity by preventing intermolecular hydrogen bonds.A nother key was the glycosylation to the branched mannose in an ether solvent, which promoted the desired glycosylation by stabilizing the oxocarbenium ion intermediate.F urthermore,h igh a-selectivity of these glycosylation reactions was realized by utilizing remote participation. Tw o asymmetrically deuterium labeled sialyl N-glycans were also synthesized by the same strategy.T he synthesized N-glycans were used to probe the molecular basis of H1N1 neuraminidase recognition. The asymmetrically deuterated N-glycans revealed ad ifference in the recognition of sialic acid on each branch. Meanwhile,t he tetraantennary N-glycan was used to evaluate the effects of multivalency and steric hinderance by forming branching structures.

The chemical synthesis of af ully sialylated tetraantennary N-glycan has been achieved for the first time by using the diacetyl strategy,i nw hich NHAc is protected as NAc 2 to improve reactivity by preventing intermolecular hydrogen bonds.A nother key was the glycosylation to the branched mannose in an ether solvent, which promoted the desired glycosylation by stabilizing the oxocarbenium ion intermediate.F urthermore,h igh a-selectivity of these glycosylation reactions was realized by utilizing remote participation. Tw o asymmetrically deuterium labeled sialyl N-glycans were also synthesized by the same strategy.T he synthesized N-glycans were used to probe the molecular basis of H1N1 neuraminidase recognition. The asymmetrically deuterated N-glycans revealed ad ifference in the recognition of sialic acid on each branch. Meanwhile,t he tetraantennary N-glycan was used to evaluate the effects of multivalency and steric hinderance by forming branching structures.

Microbial diversity in an apple orchard cultivated with natural farming practices for over 30 years was compared with conventionally farmed orchards to analyze differences in disease suppression. In this long-term naturally farmed orchard, major apple diseases were more severe than in conventional orchards but milder than in a short-term natural farming orchard. Among major fungal species in the phyllosphere, we found that Aureobasidium pullulans and Cryptococcus victoriae were significantly less abundant in long-term natural farming, while Cladosporium tenuissimum predominated. However, diversity of fungal species in the phyllosphere was not necessarily the main determinant in the disease suppression observed in natural farming; instead, the maintenance of a balanced, constant selection of fungal species under a suitable predominant species such as C. tenuissimum seemed to be the important factors. Analysis of bacteria in the phyllosphere revealed Pseudomonas graminis, a potential inducer of plant defenses, predominated in long-term natural farming in August. Rhizosphere metagenome analysis showed that Cordyceps and Arthrobotrys, fungal genera are known to include insect- or nematode-infecting species, were found only in long-term natural farming. Among soil bacteria, the genus Nitrospira was most abundant, and its level in long-term natural farming was more than double that in the conventionally farmed orchard.