Pyrroloquinoline quinone synthesis

Yield:72909-34-3 97%

Reaction Conditions:

Stage #1: 4,5-Dihydro-4,5-dioxo-1H-pyrrolo<2,3-f>chinolin-2,7,9-tricarbonsaeure-(2-ethyl)(7,9-dimethyl)esterwith lithium hydroxide;water in tetrahydrofuran at 0 - 17; for 31.5 h;
Stage #2: with hydrogenchloride;potassium chloride in tetrahydrofuran;water at 0; pH=5.3 - 6; for 1 h;
Stage #3: with sulfuric acid in water at 20; for 2.5 h;

Steps:

1.J; j; k

Into a 1-L, 3-neck flask equipped with a mechanical stirrer, a temperature probe, an addition funnel, a nitrogen purge system, and an ice bath were placed, 4,5-dioxo-4,5-dihydro- EPO lH-pynOlo[2,3-f]quinoline-2,7,9-tricarboxylic acid 2-ethyl ester 7,9-dimetliyl ester (10) (21.45 g, 0.0555 mol) and 215 mL of THF. The heterogeneous solution was stirred under nitrogen and a solution of lithium hydroxide monohydrate (11.58 g, 0.276 mol) in 515 mL of water was added over a one hour period. The temperature was held below 10 ⁰C during the addition. The reaction mixture was stirred at 16 - 17 ⁰C for 30.5 hours.Potassium chloride (15 g, 1.98 mol) was added. The flask was iced down and the pH of the reaction mixture was adjusted to approximately 6 by addition of 10.0 mL of cone, hydrochloric acid. The pH was further adjusted to 5.3 by addition of 2 N hydrochloric acid. Successive additions were required to attain a stable pH. A total of 16.0 mL of 2N hydrochloric acid was added. Stirring and cooling were continued for one hour. The red- brown solid that formed was collected by filtration, washed with a small amount of ice-water and with 100 mL of acetonitrile. The resulting red-brown triacid salt 11 was dried on the filter under a stream of nitrogen.Dried 11 (21.21 g) was dissolved in 330 mL of concentrated sulfuric acid and stirred for 2.5 hours. The acid solution was poured onto 1400 g of ice to yield a suspension of blood- red solids. The suspension was stirred with cooling for one hour. The product was collected by filtration and washed with ice-cold water. It was dried on a filter under a stream of nitrogen and then at 40 ⁰C under high vacuum to afford 17.85 g (97.4%) of the title compound. The NMR spectra indicated the presence of water even though it had been dried to near constant weight. Thermal gravimetric analysis gave an ash of 7.8%. Thermal gravimetric analysis involves heating the sample under a stream of oxygen. Any ash that remains after heating is indicative of metal (inorganic) impurities.

References:

WO2006/102642,2006,A1 Location in patent:Page/Page column 17-18; 1/6; 2/6; 3/6