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:

Synthesis of some novel thieno[3,2-d]pyrimidines as potential cytotoxic small molecules against breast cancer. A variety of novel thieno[3,2-d]pyrimidines with different decorating functional groups were synthesized as a part of a study aiming to enrich the arsenal of chemotherapeutic agents for the treatment of cancer. The design of synthetic molecules based on DNA-interchelating properties by hydrogen bond formation. The reported compounds herein are: 4-aminothienopyrimidine derivatives 4a,b and their 4-substituted phenylamino analogues 8a,b; 4-thienopyrimidin-4-ones 5a,b; N-alkyl thienopyrimidin-4-ones 6a-g; 4-chlorothienopyrimidines 7a,b; and thienopyrimidoquinazolinones 9a,b which are the structural mimics of 8a,b. The synthesized molecules were evaluated for their in vitro cytotoxic activity against human breast cancer cell line (MCF-7). Biological screening revealed varying cytotoxic potencies of the tested molecules compared with Doxorubicin as a reference drug. The cytotoxicity results from the study suggested that the synthesized molecules are potential antitumor agents and compound 4a was the most potent with an IC 50 2.04 nM.
{"Chemical": ["Doxorubicin", "N-alkyl thienopyrimidin-4-ones", "thieno[3,2-d]pyrimidines", "4-thienopyrimidin-4-ones", "hydrogen", "4-chlorothienopyrimidines", "4-aminothienopyrimidine", "thienopyrimidoquinazolinones", "4-substituted phenylamino"]}