[{"from": "human", "value": "Design a molecule that meets the criteria outlined in the description. The molecule is a methyl-branched fatty acid that is arachidic acid substituted by a methyl group at position 18. It has a role as a mammalian metabolite. It is a branched-chain saturated fatty acid, a long-chain fatty acid and a methyl-branched fatty acid. It is functionally related to an icosanoic acid."}, {"from": "gpt", "value": "[C][C][C][Branch1][C][C][C][C][C][C][C][C][C][C][C][C][C][C][C][C][C][C][C][=Branch1][C][=O][O]"}]