The present invention provides novel and advantageous compositions having a linker capable of covalently coupling one or more free thiols of an antibody. Specifically, provided herein are the molecular structures, synthetic pathways, coupling mechanisms, and applications thereof as used in an antibody-drug conjugate (ADC).本發明提供具有能夠共價偶合抗體之一或多個游離巰基的連接子的新穎且具有優勢之組合物。具體言之,本發明提供如用在抗體-藥物偶聯物(ADC)中的分子結構、合成路徑、偶合機制、及其應用。