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:

Root tubers of Lactuca tuberosa as a source of antioxidant phenolic compounds and new furofuran lignans. From the root tubers of Lactuca tuberosa, a wild edible plant species, nine phenolic compounds were isolated, including two new furofuran lignan glucosides, named lactuberin A and lactuberin B. Their structures were elucidated by spectroscopic methods, especially HRESIMS and 2D NMR techniques. This is the first time that compounds belonging to the epi series of 2,6-diaryl-3,7-dioxabicyclo[3.3.0]octane type furofuran lignans have been found in Lactuca species. The total phenolic content of the root tuber extract was evaluated and its major phenolic constituents, caffeic acid, chlorogenic acid and 3,5 dicaffeoylquinic acid, known to possess antioxidant activity, were quantified. Additionally, the root tuber extract showed DPPH radical scavenging activity implying its potential as functional food.
{"Chemical": ["furofuran lignans", "furofuran lignan glucosides", "phenolic", "lactuberin B", "3,5 dicaffeoylquinic acid", "2,6-diaryl-3,7-dioxabicyclo[3.3.0]octane", "chlorogenic acid", "caffeic acid", "DPPH", "lactuberin A"]}