4-pyridinylboronic acid

Remarkably, one year later Leadbeater described that biaryls can be synthesized via a Suzuki-type coupling under transition-metal free conditions [51, 52]. The reaction conditions were almost identical to those reported for the ligand-free process, with the difference being that a larger amoimt of Na2C03 and arylboronic acid were used. Only one successful example of a heteroaryl haUde substrate is shown namely, the coupling of 2-bromopyridine with phenylboronic acid (Scheme 32). 3-Bromothiophene did not couple under the same reaction conditions. Unfortimately, attempts to use heteroarylboronic acids such as 3-pyridinylboronic acid, 3-thienylboronic acid, and lH-indol-5-ylboronic acid on 4-bromoacetophenone completely failed. 

Progress in the synthesis of4-hydroxy-2-pyridone derivatives 12CJ0651. Recent progress in the synthesis of pyridinylboronic acids and esters 13ABJC(1)135. 

Although the above-mentioned binding pH has been reduced to 5.0, there is still an apparent gap for the direct application to urine because the pH of frequently used biosamples, particularly urine, ranges from 4.5 to 8.0. " Liu and co-workers further synthesized a pyridinylboronic acid-functionalized organic-silica hybrid monolithic capillary " to meet the broad pH range of urine samples. The preparation procedure is illustrated in Scheme 11.11. It included two steps (1) preparation of a chloropropyl-silica hybrid... 

Scheme 11.11 Schematic of the preparation procedure of 3-pyridinylboronic acid-functionalized hybrid monolithic capillary. (Reproduced from ref. 14 with permission. Copyright 2014, Elsevier BV.)...

Figure 11.11 Retention of adenosine on the 3-pyridinylboronic acid-functionalized hybrid monolithic capillary. Mobile phase 20 mM sodium phosphate buffer containing 300 mM NaCl at pH 6.0,5.5, 5.0,4.5, and 4.0, respectively, switched to 100 mM HAc (pH 2.7) at 10 min. (Reproduced from ref. 14 with permission. Copyright 2014, Elsevier BV.)...

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