The structure of the long-chain O-antigen of Yersinia pseudotuberculosis O:4b containing two uncommon deoxy sugars, tyvelose (3,6-dideoxy-d-arabino-hexose, Tyv) and 6-deoxy-d-manno-heptose (D-6dmanHep), was established by 1D and 2D NMR spectroscopy as alpha-Tyvp-(1-->3)-beta-D-6dmanHepp 1-->4 -->3)-alpha-D-Galp-(1-->3)-beta-D-GlcpNac-(1-->.