You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Structural revision of methyl tortuoate D, a bis-cembranoid from Hainan Sarcophyton tortuosum and its absolute stereochemistry. Methyl tortuoate D (1), together with five other known related bis-cembranoids, was isolated from Hainan soft coral Sarcophyton tortuosum. The structure of methyl tortuoate D (1a), firstly isolated and reported by Li et al. from the title organism, was corrected as 1 by an extensive analysis of its one-dimensional and two-dimensional nuclear magnetic resonance data and by comparison with those reported in the literature. In addition, lobophytone K (1b), recently isolated from Hainan soft coral Lobophytum pauciflorum by Lin et al., was proved to be the same compound as 1 and 1a. The absolute configuration of 1 was determined by comparing its electronic circular dichroism curve with that of co-occurring ximaolide A (2).
{"Chemical": ["bis-cembranoid", "ximaolide A", "lobophytone K", "bis-cembranoids", "methyl tortuoate D", "Methyl tortuoate D"]}