The present invention provides a compound that has an exceptional TLR4 signal-inhibiting action and can be useful as a drug for the prevention or treatment of autoimmune diseases and/or inflammatory diseases or diseases such as chemotherapy-induced peripheral neuropathy (CIPN), chemotherapy-induced neuropathic pain (CINP), liver disorders, ischemic reperfusion injury (IRI), etc. The present invention pertains to ethyl 6-((2-chloro-4-fluorobenzyl)sulfonyl)-3-hydroxycyclohex-1-ene-1-carboxylate or optical isomers thereof.