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Dehydroabietic acid (50 mg, 0.116 μmol, Helix Biotech) was dissolved in 2 ml of methanol (HPLC grade, Fisher Scientific) and cooled to 0° C. on ice in a round bottom flask. An excess (30 μmol) of ethereal diazomethane (obtained by distillation) was added and the reaction was stirred for 5 minutes. The non-reacted diazomethane was evaporated and solvent was then removed by rotary evaporation. This reaction is shown schematically in FIG. 4. The product was purified by preparative TLC (1000 μm PK6F 60 Å, Whatman) silica gel plates developed in hexane:ethyl acetate 95:5 (v:v, Rf: 0.25). This step provided 30 mg of a clear oil as the methyl ester that was pure by NMR (see FIG. 5). 1H NMR (CDCl3, 300 MHz) δ1.35-1.42 (m, 12H), 1.50-2.05 (m, 7H), 2.43 (t, J=8.80 Hz, 2H), 2.90-3.05 (m, 3H), 3.80 (s, 3H), 7.02 (s, 1H), 7.14 (d, J=8.19 Hz, 1H), 7.31 (d, J=8.19 Hz, 1H). The product also gave the following electron impact mass spectra: (%) 315 (2.9, M+1), 314 (13, M), 299 (16.4), 240 (20.1), 239 (100), 197 (6.1), 173 (5.0), 141 (5.7).

1. customThe non-reacted diazomethane was evaporated
2. customsolvent was then removed by rotary evaporation
3. customThe product was purified by preparative TLC (1000 μm PK6F 60 Å, Whatman) silica gel plates