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 and biochemical activities of antiproliferative amino acid and phosphate derivatives of microtubule-disrupting β-lactam combretastatins. The synthesis and biochemical activities of novel water-soluble β-lactam analogues of combretastatin A-4 are described. The first series of compounds investigated, β-lactam phosphate esters 7a, 8a and 9a, exhibited potent antiproliferative activity and caused microtubule disruption in human breast carcinoma-derived MCF-7 cells. They did not inhibit tubulin polymerisation in vitro, indicating that biotransformation was necessary for their antiproliferative and tubulin binding effects in MCF-7 cells. The second series of compounds, β-lactam amino acid amides (including 10k and 11l) displayed potent antiproliferative activity in MCF-7 cells, disrupted microtubules in MCF-7 cells and also inhibited the polymerisation of tubulin in vitro. This indicates that the β-lactam amides did not require metabolic activation to have antiproliferative effects, in contrast to the phosphate series. Both series of compounds caused mitotic catastrophe and apoptosis in MCF-7 cells. Molecular modelling studies indicated potential binding conformations for the β-lactam amino acid amides 10k and 11l in the colchicine-binding site of tubulin. Due to their aqueous solubility and potent biochemical effects, these compounds are promising candidates for further development as microtubule-disrupting agents.
{"Chemical": ["\u03b2-lactam", "combretastatin A-4", "amino acid", "\u03b2-lactam phosphate esters", "\u03b2-lactam amides", "phosphate", "colchicine", "\u03b2-lactam combretastatins", "\u03b2-lactam amino acid amides"]}