The size of the polar head group plays a key role in lipid biophysics, influencing membrane organization, phase behavior, including transition (melting) temperature, as well as lipid–lipid interactions, such as the umbrella effect. In general, small head groups are associated with high transition temperatures and tighter head group packing compared to lipids with large head groups. The head groups of phosphatidylglucoside (PtdGlc) and phosphatidylinositol (PtdIns) are configurational isomers with both featuring a six-membered ring and a similar number of hydroxy functions. Interestingly, their chemical stability and biophysical properties differ significantly, despite their high structural similarity, comparable chemical size and weight, and presumably analogous head group orientation relative to the plasma membrane normal. PtdIns is known to exhibit a low transition temperature, limited lipid–lipid head group interaction, a high degree of head group hydration and an intramolecular hydrogen-bond even under fully hydrated conditions. PtdGlc on the other hand exhibits a ~20 degree higher transition temperature, extensive lipid–lipid head group interactions, a low degree of head group hydration and no intramolecular hydrogen-bond. Consequently, head group size in terms of lipid biophysics, refers not only to the immediate chemical size, but also includes the primary hydration shell.

Oligosaccharides of glycoproteins have important functions in many biological processes. Complex-type oligosaccharides are major structures of asparagine-linked oligosaccharides and have unique antennary structures, such as bi-, tri-, and tetra-antennary forms. Here, we describe a novel method for semisynthesis of two types of naturally occurring complex-type triantennary oligosaccharides, 1 and 2, in 9 and 10 conversion steps, respectively. The semisynthesis employed a biantennary oligosaccharide isolated from a natural source as a starting material. A benzylidenation reaction enabled selective protection of 8 hydroxy groups, among the 24 hydroxy groups of the biantennary oligosaccharide. Furthermore, selective debenzylidenation of mannoside residues successfully produced two types of suitably protected oligosaccharyl acceptors. Glycosylation with a disaccharide donor and subsequent deprotection steps yielded two types of intact complex-type triantennary oligosaccharides.

糖タンパク質上の糖鎖は種々の重要な生命現象に関与している。アスパラギン結合型糖鎖の中で複合型糖鎖は主要な糖鎖構造であり、二・三・四分枝といった独特な分枝構造を有する。本論文では、天然に見られる二種類の複合型三分枝糖鎖へと9及び10工程で変換できる、新しい半合成法について述べる。この戦略では天然試料から大量調製可能な二分枝複合型糖鎖を出発原料として用いた。まずベンジリデン化反応により、原料が持つ24個の水酸基の中から8個の水酸基のみを選択的に保護した。また、種々の検討を重ねる中で、マンノース残基における選択的な脱ベンジリデン化反応を見出した。これにより二種類の糖受容体を得た。別途合成した二糖供与体とのグリコシル化反応によって三分枝糖鎖へと導き、数工程での脱保護反応によって望む二種類の三分枝糖鎖をそれぞれ合成した。