A process for forming a boronic acid anhydride of a compound of formula: comprising the steps: coupling a trifluoroacetic acid addition salt of a compound of formula (XVIII): with a compound of formula ( XIXa): wherein the moiety -C X is an activated ester generated in situ by contacting N-(2-pyrazinecarbonyl)-L-phenylalanine with dicyclohexylcarbodiimide and N-hydroxysuccinimide, wherein the moiety C -X is an O-(N-hydroxysuccinimide)ester, to form a compound of formula ( XXIII): and deprotecting the boronic acid moiety to form a boronic acid anhydride of the compound of formula; wherein the coupling step comprises: (i) providing a solution of (1 R)- -pinanediol 1-ammonium trifluoroacetate-3-methylbutane-1-boronate and N-hydroxysuccinimide, followed by addition of dicyclohexylcarbodiimide to form a suspension; (ii) providing a solution of N-(2-pyrazinecarbonyl)-L-phenylalanine and adding N-methylmorpholine thereto; (iii) adding the solution resulting from step (ii) to the suspension resulting from step (i) and optionally adjusting the resulting suspension to pH 7 by adding N-methylmorpholine; and wherein coupling step (i) comprises providing a solution of (1 R)- -pinanediol 1-ammonium trifluoroacetate-3-methylbutane-1-boronate and N-hydroxysuccinimide in DMF, followed by addition of dicyclohexylcarbodiimide to form a suspension; and/or coupling step (ii) comprises providing a solution of N-(2-pyrazinecarbonyl)-L-phenylalanine in DMF and adding N-methylmorpholine thereto. coupling a trifluoroacetic acid addition salt of a compound of formula (XVIII): with a compound of formula ( XIXa): wherein the moiety -C X is an activated ester generated in situ by contacting N-(2-pyrazinecarbonyl)-L-phenylalanine with dicyclohexylcarbodiimide and N-hydroxysuccinimide, wherein the moiety C -X is an O-(N-hydroxysuccinimide)ester, to form a compound of formula ( XXIII): and deprotecting the boronic acid moiety to form a boronic acid anhydride of the compound of formula; wherein the coupling step comprises: (i) providing a solution of (1 R)- -pinanediol 1-ammonium trifluoroacetate-3-methylbutane-1-boronate and N-hydroxysuccinimide, followed by addition of dicyclohexylcarbodiimide to form a suspension; (ii) providing a solution of N-(2-pyrazinecarbonyl)-L-phenylalanine and adding N-methylmorpholine thereto; (iii) adding the solution resulting from step (ii) to the suspension resulting from step (i) and optionally adjusting the resulting suspension to pH 7 by adding N-methylmorpholine; and wherein coupling step (i) comprises providing a solution of (1 R)- -pinanediol 1-ammonium trifluoroacetate-3-methylbutane-1-boronate and N-hydroxysuccinimide in DMF, followed by addition of dicyclohexylcarbodiimide to form a suspension; and/or coupling step (ii) comprises providing a solution of N-(2-pyrazinecarbonyl)-L-phenylalanine in DMF and adding N-methylmorpholine thereto. (i) providing a solution of (1 R)- -pinanediol 1-ammonium trifluoroacetate-3-methylbutane-1-boronate and N-hydroxysuccinimide, followed by addition of dicyclohexylcarbodiimide to form a suspension; (ii) providing a solution of N-(2-pyrazinecarbonyl)-L-phenylalanine and adding N-methylmorpholine thereto; (iii) adding the solution resulting from step (ii) to the suspension resulting from step (i) and optionally adjusting the resulting suspension to pH 7 by adding N-methylmorpholine; and