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Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).
The structure of vitamin K1 (phylloquinone) and K2 (menaquinone, MK), where the number n indicates the number of isoprenyl groups (4–10) at the C3 position. The structure without a side chain is called menadione (vitamin K3) and is, as such, without vitamin K activity.