A synthetic Antrodia cinnamomea galactomannan library by frameshift unveils a potent immunoregulatory octasaccharide domain

We report the design, synthesis, and immunological evaluation of an Antrodia cinnamomea galactomannan library consisting of 11 oligosaccharides, with chain lengths ranging from 4 to 24 sugars. These oligosaccharides maintain a consistent composition of 75% mannose and 25% galactose, mirroring the key structural features of natural galactomannan. Notably, the library includes five tetrasaccharides and four octasaccharides, exhibiting all possible frameshift patterns of A. cinnamomea galactomannan, offering valuable materials for structure-activity relationship studies to explore the role of linking modes and domain effect. The synthesis of this library was achieved through a highly effective stereoselective α-galactosylation approach. Immunological evaluations revealed that octasaccharide 4 and its two subunit tetrasaccharides 7 and 10 exhibited potent immunoregulatory activities, demonstrating a notable domain effect. Preliminary mechanistic studies unveiled that these oligosaccharides exert their effects by suppressing mitogen-activated protein kinase signaling pathway. In addition, octasaccharide 4 uniquely attenuated nuclear factor κB pathway, highlighting its compound-specific mechanism and demonstrating a 1 + 1 > 2 effect.