Inhibition of the programmed cell death-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) interaction using small-molecule inhibitors is an emerging immunotherapeutic approach. A novel series of [1,2,4]­triazolo­[4,3-a]­pyridines were designed and found to be potent inhibitors of the PD-1/PD-L1 interaction. Among them, compound A22 exhibited the most potent activity, as assessed by homogenous time-resolved fluorescence assay, with an IC50 of 92.3 nM. Furthermore, A22 dose-dependent elevated interferon-γ production in a co-culture model of Hep3B/OS-8/hPD-L1 and CD3 T cells. We concluded that A22 is a promising lead compound for the development of inhibitors of the PD-1/PD-L1 interaction. In addition, we explored the structure–activity relationships of the newly synthesized [1,2,4]­triazolo­[4,3-a]­pyridines and demonstrated that a ring fusion strategy can be employed for designing analogues of the Bristol-Myers Squibb chemical series. These studies pave the way for future drug design.

Through specific structural modification of a 4-phenylindoline precursor, new 4-arylindolines containing a thiazole moiety were developed and found to be promising modulators of the programmed cell death-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) axis. Compound A30 exhibited outstanding biochemical activity, with an IC50 of 11.2 nM in a homogeneous time-resolved fluorescence assay. In the cell-based assay, A30 significantly promoted IFN-γ secretion and rescued T-cell proliferation, which were inhibited by PD-1 activation. Furthermore, A30 showed favorable in vivo antitumor activity in a mouse 4T1 breast carcinoma model. Moreover, in mouse CT26 colon carcinoma models, A30 potently suppressed the growth of CT26/PD-L1 tumor but did not obviously affect the growth of CT26/vector tumor. The results of flow cytometry analysis indicated that A30 inhibited tumor growth by activating the immune microenvironment. We concluded that A30 is a new starting point for further development of PD-1/PD-L1 interaction inhibitors as antitumor agents.

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A novel method is reported for the stereoselective synthesis of highly functionalized allyl aryl sulfones. This protocol is based on a Pdcatalyzed three-component tandem reaction of sulfonyl hydrazides and aryl iodides with allenes and exhibits high (Z)-selectivity, good yields, minimal waste, ample product scope, and operational simplicity.

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