Acetic Anhydride → 1-(5-Carboxy-pentyl)-4-[5-(1-ethyl-3,3-dimethyl-5-phosphono-1,3-dihydro-indol-2-ylidene)-penta-1,3-dienyl]-quinolinium chloride

Participants

Reaction Conditions

Reaction Steps

To a 50 mL flask were added 6 (0.25 g, 0.93 mmol), malonaldehyde dianilide hydrochloride (0.25 g, 0.97 mmol), acetic acid (4 mL) and acetic anhydride (4 mL). The mixture was heated at 110° C. for 90 min and then was cooled to rt. The volatile components were removed under vacuum to leave a tar. The tar was dissolved in acetic acid (4 mL) and then pyridine (5 mL) and 14 (0.34 g, 0.89 mmol) were added. The mixture was heated at 110° C. for 25 min and then cooled to rt. The volatile components were removed under vacuum to leave a dark blue tar that was dissolved in conc. HCl (20 mL). After stirring for 3 h, the mixture was diluted with water (150 mL) and then basified, first by addition of 4 M sodium hydroxide solution until the pH was approx. 4 and then with saturated sodium bicarbonate solution. The fluorescent product initially precipitated from the mixture but then re-dissolved. The aqueous solution was loaded onto a column of C-18 reverse-phase silica gel (4×15 cm) in water. The column was eluted with water to remove the salts and excess base, with 1 M HCl to generate the free acid of the fluorescent compound and then with water to remove the excess acid. Gradient elution from 0-55% methanol in water (5% steps of 500 mL-1 L) first eluted the symmetrical bisphosphonic acid fluorescent compound and then fluorescent compound 15. The fractions were evaporated in vacuo to leave a blue residue that was taken up in methanol (70 mL) and filtered through a medium frit. Water (30 mL) was added and then the solvent mixture was removed in vacuo to afford fluorescent compound 15 as a blue solid.

Provenance & Evidence