vitamin k2

 one of the two K vitamins, actually a mixture of homologous fat-soluble substituted naphthoquinones (called menaquinones), (C11H7O2[C5H8]nH), where n may be 1 to 13 but is mostly 7 to 9. The term is also used for synthetic compounds resembling vitamin K2 and having the same physiological action. The individual components of vitamin K2 are also referred to by the number of isoprenyl units in the side chain (the number n in the formula), as for menadione, having no units at that position of the naphthaquinone ring, and also called vitamin K2(0) (and also called vitamin K3).  [WordNet 1.5]