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:

Structure and Absolute Configuration of Methyl (3R)-Malonyl-(13S)-hydroxycheilanth-17-en-19-oate, a Sesterterpene Derivative from the Roots of Aletris farinosa. We report the isolation and structure elucidation of a new cheilanthane sesterterpene from the roots of Aletris farinosa that possesses an unusual malonate half-ester functional group. The structure of 1 was determined via mass spectrometry and 1D and 2D NMR spectroscopy, while its absolute configuration was determined via X-ray crystallographic analysis performed on its methyl ester derivative 2.
{"Chemical": ["Sesterterpene", "methyl ester", "sesterterpene", "malonate half-ester", "cheilanthane", "Methyl (3R)-Malonyl-(13S)-hydroxycheilanth-17-en-19-oate"]}