Μ-opioid receptor agonist and preparation method therefor and use thereof in field of medicine

A compound represented by the general formula I, and stereoisomers, tautomers, enantiomers, diastereomers, racemates, and pharmaceutically acceptable salts thereof,

• wherein,
• Ar1 is a substituted or unsubstituted aryl, a substituted or unsubstituted heteroaryl;
• A is a —C1-2 alkylene, or a —C1-3 alkyl-substituted —C1-2 alkylene;
• B is —NH—CH2—Ar2, —NH—C(O)—Ar2 or —NR1R2, wherein
• R1 and R2 together with the nitrogen atom to which they are attached form a 6-12 membered heteroaryl substituted by T or unsubstituted, T is —H, —OH, —C1-3 alkyl, —C1-3 alkoxy, hydroxyl-substituted C1-3 alkyl, halogen-substituted C1-3 alkyl, halogen-substituted C1-3 alkoxy, halogen, amino, mono (C1-3 alkyl) -amino-, bis (C1-3 alkyl) -amino-, nitrile group, benzyl or phenyl;
• Ar2 is a substituted or unsubstituted phenyl, a substituted or unsubstituted 5-6 membered heteroaryl, wherein the phenyl or the 5-6 membered heteroaryl is optionally substituted by one or more of the following substituents:
• —OH, halogen, nitrile group, —C1-3 alkyl, —C1-3 alkoxy, hydroxyl-substituted C1-3 alkyl, halogen-substituted C1-3 alkyl, halogen-substituted C1-3 alkoxy, amino, mono (C1-3 alkyl) -amino-, bis (C1-3 alkyl)-amino-, benzyl or phenyl.