1H-n.m.r. analysis of type-2 chain lacto-gangliosides. Confirmation of structure of a novel cancer-associated fucoganglioside, α-NeuAc-(2→6)-β-d-Galp-(1→4)-β-d- GlcpNAc-(1→3)-β-d-Galp-(1→4)-[α-l-Fucp-(1→3)]-β-d-GlcpNAc-(1→3)-β-d-Galp-(1→4)-β-d- Glcp-(1→1)-Cer (VI6NeuAcIII3FucnLc6Cer)