Benzoxazinone (III) was obtained by the two-step condensation of methyl 3-amino-4-hydroxybenzoate (I) and 2-bromoisobutyryl bromide (II), first with NaHCO3 in H2O-EtOAc to afford the corresponding amide, and then cyclization with K2CO3 in DMF. Subsequent N-alkylation of (III) with 2-iodopropane (IV) in the presence of NaH in DMF at 60 C provided the isopropylated compound (V). Refluxing of (V) with an excess of guanidine (VI) in MeOH yielded the desired acylguanidine, which was finally converted to the mesylate salt upon treatment with methanesulfonic acid in isopropanol.
The alkylation of 3-amino-4-hydroxybenzoic acid methyl ester (I) with isopropyl iodide and NaHCO3 gives 4-hydroxy-3-(isopropylamino)benzoic acid methyl ester (II), which is esterified with 2-bromoisobutyryl bromide (III) and TEA to yield 4-(2-bromoisobutyryloxy)-3-(isopropylamino)benzoic acid methyl ester (IV). The O-N migration of the 2-bromoisobutyryl group of (IV) catalyzed by acetic acid affords the 2-bromoisobutyrylamide (V), which is cyclized by means of K2CO3 to provide 4-isopropyl-2,2-dimethyl-3-oxo-3,4-dihydro-2H-1,4-benzoxazine-6-carboxylic acid methyl ester (VI). Finally, this compound is condensed with guanidine and treated with MeSO3H to give the target mesylate.