Understanding the Boron–Nitrogen Interaction and Its Possible Implications in Drug Design

Gating and regulation of the calcium release-activated calcium channel: Recent progress from experiments and molecular modeling

Calcium release-activated calcium (CRAC) channels are highly calcium ion (Ca²⁺)-selective channels in the plasma membrane. The transient drop of endoplasmic reticulum Ca²⁺ level activates its calcium sensor stromal interaction molecule (STIM) and then triggers the gating of the CRAC channel pore unit Orai. This process involves a variety of activities of the immune system. Therefore, understanding how the activation and regulation of the CRAC channel can be accomplished is essential. Here we briefly summarize the recent progress on Orai gating and its regulation by 2-aminoethoxydiphenylborate (2-APB) obtained from structural biology studies, biochemical and electrophysiological measurements, as well as molecular modeling. Indeed, integration between experiments and computations has further deepened our understanding of the channel gating and regulation.

In Vivo Targeting Using Arylboronate/Nopoldiol Click Conjugation

Bioorthogonal click reactions yielding stable and irreversible adducts are in high demand for in vivo applications, including in biomolecular labeling, diagnostic imaging, and drug delivery. Previously, we reported a novel bioorthogonal "click" reaction based on the coupling of ortho-acetyl arylboronates and thiosemicarbazide-functionalized nopoldiol. We now report that a detailed structural analysis of the arylboronate/nopoldiol adduct by X-ray crystallography and ¹¹B NMR reveals that the bioorthogonal reactants form, unexpectedly, a tetracyclic adduct through the cyclization of the distal nitrogen into the semithiocarbazone leading to a strong B-N dative bond and two new 5-membered rings. The cyclization adduct, which protects the boronate unit against hydrolytic breakdown, sheds light on the irreversible nature of this polycondensation. The potential of this reaction to work in a live animal setting was studied through in vivo capture of fluorescently labeled molecules in vivo. Arylboronates were introduced into tissues through intradermal injection of their activated NHS esters, which react with amines in the extracellular matrix. Fluorescently labeled nopoldiol molecules were administered systemically and were efficiently captured by the arylboronic acids in a location-specific manner. Taken together, these in vivo proof-of-concept studies establish arylboronate/nopoldiol bioorthogonal chemistry as a candidate for wide array of applications in chemical biology and drug delivery.

Entropy and Polarity Control the Partition and Transportation of Drug-like Molecules in Biological Membrane

Partition and transportation of drug in the plasma membrane of a mammalian cell are the prerequisite for its function on target protein. Therefore, comprehensive understanding of the physicochemical properties and mechanism behind these complex phenomena is crucial in pharmaceutical research. By using the state-of-art molecular simulations with polarization effect implicitly or explicitly included, we studied the permeation behavior of 2-aminoethoxydiphenyl borate (2-APB), a broad-spectrum modulator for a number of membrane proteins. We showed that the protonation state and therefore the polarity of the drug is critical for its partition, and that the drug is likely to switch between different protonation states along its permeation pathway. By changing the degrees of freedom, protonation further affects the thermodynamic of the permeation pathway of 2-APB, leading to different entropic contributions. A survey on 54 analog structures with similar backbone to 2-APB showed that delicate balance between entropy and polarity plays an important role in drugs’ potency.