Multivalent interaction is often used in molecular design and leads to engineered multivalent ligands with increased binding avidities toward target molecules. The resulting binding avidity relies critically on the rigid scaffold that joins multiple ligands as the scaffold controls the relative spatial positions and orientations toward target molecules. Currently, no general design rules exist to construct a simple and rigid DNA scaffold for properly joining multiple ligands. Herein, we report a crystal structure-guided strategy for the rational design of a rigid bivalent aptamer with precise control over spatial separation and orientation. Such a pre-organization allows the two aptamer moieties simultaneously to bind to the target protein at their native conformations. The bivalent aptamer binding has been extensively characterized, and an enhanced binding has been clearly observed. This strategy, we believe, could potentially be generally applicable to design multivalent aptamers.

A series of novel potentially platelet aggregation-inhibiting 1,4-benzoxazine-3(4H)-one derivatives was designed and synthesized through Smiles rearrangement, reduction and acetylation reactions. The antiaggregatory activities of the target molecules on arterial blood samples from rabbits, expressed by IC 50 values (μM), were then evaluated in vitro against ADP induced platelet aggregation. The favorable IC 50 values of compound 8c (IC 50 8.99 µM) and 8d (IC 50 8.94 µM) indicated that these two compounds were the most potent molecules among all the synthesized compounds. A detailed molecular docking study to explore the interaction of compounds 8c and 8d with GP IIb/IIIa receptor showed that they these two compounds were docked into the active site of GPIIb/IIIa receptor. These results suggest that the 1,4-benzoxazine-3(4H)-one derivatives are promising lead compounds to develop new platelet aggregation inhibitors.

A new pH-sensitive rhodamine derivative was designed and synthesized using coupling reaction of rhodamine hydrazine with commercially available 3-bromo-4-hydroxybenzaldehyde, and characterized via NMR, HRMS, UV and fluorescent spectra. The obtained probe was marked with yellow fluorescence under neutral condition and pink in strongly acidic media. It has high quantum yields, is not susceptible to metal interference, and has high penetration ability for cell membrane and also further applicable in bioimaging.