Fig. 1

2D-NMR-HSQC spectra (δ_C/δ_H 53–150/2.0–8.0) of a untreated sugarcane bagasse; b sugarcane bagasse pretreated with 2.5% Na₂SO₃ + 1.25% NaOH; c sugarcane bagasse pretreated with 5.0% Na₂SO₃ + 2.5% NaOH; d sugarcane bagasse pretreated with 10% Na₂SO₃ + 5.0% NaOH; and e reference-delignified sugarcane bagasse treated with sodium chlorite for 2 h. See Additional file 2: Table S1 for signal assignments. The main structures present in the sugarcane bagasse samples are A: β-O-4′ alkyl-aryl ethers; A′: γ-p-coumaroylated β-O-4′ alkyl-aryl ethers; B: β-5′ phenylcoumarans; I: cinnamyl alcohol end-groups; pCA: p-coumaric acid units; FA: ferulic acid units; H: p-hydroxyphenyl units; G: guaiacyl units; S: syringyl units; X: xylans; X′: acetylated xylans; and U: 4-O methyl-α-d-glucuronic acid. Note that the regions for C_α/H_α correlation signal of phenylcoumarans (B_α) and the H_2,6 correlation signals of H-lignin units have been magnified for better viewing