2-Aminoethoxydiphenyl Borate as a Prototype Drug for a Group of Structurally Related Calcium Channel Blockers in Human Platelets

Abstract

We have synthesized a series of 2-aminoethoxydiphenyl borate (2-APB, 2,2-diphenyl-1,3,2-oxazaborolidine) analogs and tested their ability to inhibit thrombin-induced Ca 2ϩ influx in human platelets. The analogs were either synthesized by adding various substituents to the oxazaborolidine ring (methyl, dimethyl, tert-butyl, phenyl, methyl phenyl, and pyridyl) or increasing the size of the oxazaborolidine ring to seven-and nine-membered rings. NMR analysis of the boron-containing analogs suggests that each of them exist as a ring structure through the formation of an N3 B coordinate bond (except for the hexyl analog). The possibility that these boron-containing compounds formed dimers was also considered. All compounds dose-dependently inhibited thrombin-induced Ca 2ϩ influx in human platelets, with the 2,2-diphenyl-1,3,2-oxazaborolidine-5-one derivative having the weakest activity at 100 M, whereas the (S)-4-benzyl and (R)-4-benzyl derivatives of 2-APB were approximately 10 times more potent than the parent 2-APB. Two nonboron analogs (3-methyl and 3-tert-butyl 2,2-diphenyl-1,3-oxazolidine) were synthesized; they had approximately the same activity as 2-APB, and this implies that the presence of boron was not necessary for inhibitory activity. All of the compounds tested were also able to inhibit thrombininduced calcium release. We concluded that extensive modifications of the oxazaborolidine ring in 2-APB can be made, and Ca 2ϩ -blocking activity was maintained.2-Aminoethoxydiphenyl borate (2-APB; systematic name: 2,2-diphenyl-1,3,2-oxazaborolidine, compound 1) was originally described as an inhibitor of inositol 1,4,5-trisphosphate receptors (IP 3 R) in a variety of cells (Maruyama et al., 1997) and has been extensively used as a probe for examining calcium influx processes. 2-APB was inappropriately used in several studies to imply that IP 3 Rs were involved in storeoperated Ca 2ϩ entry (SOCE) . For a review of our current understanding of the nature of SOCE and how the SOCE channels are regulated, see Parekh and Putney (2005). It has been suggested that SOCE is mediated by members of the transient receptor potential canonical (TRPC), family although this has not been accepted universally (Parekh and Putney, 2005).Upon further investigation, it became evident that 2-APB, along with inhibition of IP 3 Rs, was also inhibiting SOCE directly in several cell types (Bakowski et al., 2001;Broad et al., 2001;Diver et al., 2001;Dobrydneva et al., , 2002Gregory et al., 2001;Iwasaki et al., 2001;Ma et al., 2001;Prakriya and Lewis, 2001;Bootman et al., 2002). The inhibition of SOCE seemed to be at an extracellular site by a mechanism not involving intracellular IP 3 Rs. In our study showing that 2-APB blocked SOCE in human platelets (Dobrydneva and Blackmore, 2001), we tested whether several other structurally related compounds were also inhibitors of SOCE. We Some of the findings in this manuscript were presented at two meetings of the Virginia Academy of Science (Dovel et al., 2002;Thadigiri et al., 2003) and ...

Antithrombotic Potential of Blockers of Store-Operated Calcium Channels in Platelets

“…mast cells, 23 whereas the structural analog GSK-7975A has not been tested before. The compound 2APB was previously considered to be an antagonist of InsP 3 receptors but later identified as a much more potent Ca 2+ influx blocker, 24,25,30 which is confirmed by the current data. Other tested compounds were much less effective in inhibiting SOCE and could not be used in the presence of blood plasma (ie, MRS1845 and SKF96365, the first described antagonist of Ca 2+ influx in isolated platelets and leukocytes).…”

“…Candidate compounds tested included the known SOCE inhibitor, bimethoxyphenyl imidazole, SKF96365 22 ; the less well-studied lipophilic biaromates, Synta66 and GSK-7975A ( Figure I in the online-only Data Supplement) 23 ; and furthermore the diphenylborate 2APB, initially used as InsP 3 receptor inhibitor at high concentrations but now recognized as a more potent antagonist of Ca 2+ entry. 24,25 Other tested compounds were LOE-908Cl and the nitrophenyl pyridine, MRS1845, both of which block Ca 2+ entry in HL-60 cells. 26,27 Because platelets lack voltage-dependent Ca 2+ channels, 3 specific inhibitors of these were not tested.…”

Potentiation of the store-operated calcium entry (SOCE) induces phytohemagglutinin-activated Jurkat T cell apoptosis

“…Depending on the concentration, 2-APB can inhibit IP 3 Rs, sarco-and endoplasmic Ca 2+ ATPase (SERCA) pumps, as well as some transient receptor potential (TRP) channels of the TRPC family [21][22][23][24][25] while opening some members of the TRPV family [26,27]. A few teams have already documented the synthesis of 2-APB analogues, but only with the purpose of developing more specific inhibitors [28][29][30][31][32].…”

Theoretical Characterization of Three 2,2-Diphenyl-1,3,2-oxazaborolidin-5-ones: Molecules with Fungicide Activities

“…In the current study, the distance between B 2 N 3 atoms of the presented 2,2-diphenyl-1,3,2-oxazaborolidin-5-ones was demonstrated to be modified by the amino acid residue on C 4 . This residue also modifies the charges of the heterocyclic atoms.…”

“…In the fields of both apoptosis and fungal infections, much interest is currently focused on boroncontaining molecules, since many compounds with boron-nitrogen bonds have shown insecticidal, antineoplastic, herbicidal, fungicidal, and antibacterial activities [3][4][5][6]. In this class of nitrogen-boron coordinated compounds, there is a group that required special attention, the 2,2-diphenyl-1,3,-oxazaborolidin-5-ones that are obtained from diphenyl borinic acid and an -amino acid.…”