A mixture of 6-(3-chloro-4-fluorobenzyl)-3,4-dihydroxy-N,N-dimethyl-5-oxo-5,6,7,8-tetrahydro-2,6-naphthyridine-1-carboxamide (3.99 g, 10.511 mmol; Example 1, step 9) and magnesium methoxide in methanol (52.4 mL, 6-10% methanol solution available from Aldrich) in DMSO (100 mL) was heated at 60° C. for 30 minutes. Methanol was exhaustively removed under vacuum over 45 minutes. The residual DMSO solution was treated with allyl bromide (3.810 g, 31.52 mmol) and stirred at room temperature under an atmosphere of nitrogen for overnight. The reaction mixture was treated dilute hydrochloric acid. The solid precipitated was filtered to provide the title compound. (ES MS M+1=421.2)
