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:

3-Hydroxyazetidine carboxylic acids: non-proteinogenic amino acids for medicinal chemists. The formation from D-glucose of both enantiomers of 2,4-dideoxy-2,4-iminoribonic acid is the first chemical synthesis of unprotected 3-hydroxyazetidine carboxylic acids. The long-term stability of 3-hydroxyazetidine amides is established at acidic and neutral pH and implies their value as non-proteinogenic amino acid components of peptides, providing medicinal chemists with a new class of peptide isosteres. The structure of N,3-O-dibenzyl-2,4-dideoxy-2,4-imino-D-ribonic acid was established by X-ray crystallographic analysis. An N-methylazetidine amide derivative is a specific inhibitor of β-hexosaminidases at the micromolar level, and is only the second example of potent inhibition of any glycosidase by an amide of a sugar amino acid related to an iminosugar.
{"Chemical": ["sugar amino acid", "3-Hydroxyazetidine carboxylic acids", "amide", "amino acids", "iminosugar", "amino acid", "N,3-O-dibenzyl-2,4-dideoxy-2,4-imino-D-ribonic acid", "2,4-dideoxy-2,4-iminoribonic acid", "D-glucose", "3-hydroxyazetidine carboxylic acids", "N-methylazetidine amide", "3-hydroxyazetidine amides"]}