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:

Cytotoxic pentacyclic triterpenoids from Prinsepia utilis. Phytochemical investigation of the aerial parts of Prinsepia utilis Royle resulted in the isolation and identification of ten pentacyclic triterpenoids, including two new triterpenoids, 2α-O-trans-p-coumaroyl-3β,19α-dihydroxy-urs-12-en-28-oic acid (1) and 2α-O-cis-p-coumaroyl-3β,19α-dihydroxy-urs-12-en-28-oic acid (2), along with eight known pentacyclic triterpenoids (3-10). The structures were elucidated by extensive spectroscopic methods and by comparison to previously reported spectroscopic data. Most of these compounds showed significant cytotoxic activities against four human cancer cell lines (A549, HCT116, MDA-MB-231, and CCRF-CEM), and the structure-activity relationships are also discussed.
{"Chemical": ["pentacyclic triterpenoids", "triterpenoids", "2\u03b1-O-trans-p-coumaroyl-3\u03b2,19\u03b1-dihydroxy-urs-12-en-28-oic acid", "2\u03b1-O-cis-p-coumaroyl-3\u03b2,19\u03b1-dihydroxy-urs-12-en-28-oic acid"]}