The present invention relates to the field of medical chemistry, and relates to a heterocyclic compound serving as a PD-L1 inhibitor. Specifically, the present invention relates to a compound represented by formula A, or an isomer, pharmaceutically acceptable salt, solvate or prodrug thereof, preparation methods therefor, a pharmaceutical composition containing these compounds, and a use of these compounds or composition in treating cancers or infectious diseases.本發明屬醫藥化學領域，涉及一類作為PD-L1抑制劑的雜環類化合物及其應用，具體地，本發明涉及通式A所示的化合物或其異構體、藥學上可接受的鹽、溶劑合物或前藥，它們的製備方法以及含有該些化合物的藥物組合物和該些化合物或組合物用於治療癌症或者感染類疾病的用途。
