GO:0009234

The chemical reactions and pathways resulting in the formation of any of the menaquinones, any of the quinone-derived compounds synthesized by intestinal bacteria. Structurally, menaquinones consist of a methylated naphthoquinone ring structure and side chains composed of a variable number of unsaturated isoprenoid residues. Menaquinones have vitamin K activity and are known as vitamin K2. [GOC:jl, http://www.dentistry.leeds.ac.uk/biochem/thcme/vitamins.html#k]