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:

Structural Modifications to Tetrahydropyridine-3-carboxylate Esters en Route to the Discovery of M(5)-Preferring Muscarinic Receptor Orthosteric Antagonists. The M(5) muscarinic acetylcholine receptor is suggested to be a potential pharmacotherapeutic target for the treatment of drug abuse. We describe herein the discovery of a series of M(5)-preferring orthosteric antagonists based on the scaffold of 1,2,5,6-tetrahydropyridine-3-carboxylic acid. Compound 56, the most selective compound in this series, possesses an 11-fold selectivity for the M(5) over M(1) receptor and shows little activity at M(2)-M(4). This compound, although exhibiting modest affinity (K(i) = 2.24 μM) for the [(3)H]N-methylscopolamine binding site on the M(5) receptor, is potent (IC(50) = 0.45 nM) in inhibiting oxotremorine-evoked [(3)H]DA release from rat striatal slices. Further, a homology model of human M(5) receptor based on the crystal structure of the rat M(3) receptor was constructed, and docking studies of compounds 28 and 56 were performed in an attempt to understand the possible binding mode of these novel analogues to the receptor.
{"Chemical": ["[(3)H]N-methylscopolamine", "oxotremorine", "acetylcholine", "1,2,5,6-tetrahydropyridine-3-carboxylic acid", "[(3)H]DA", "Tetrahydropyridine-3-carboxylate Esters"]}