[C:1]1([CH3:20])[CH:6]=[CH:5][C:4]([NH:7][C:8]2[CH:16]=[C:15]([C:17]([OH:19])=[O:18])[CH:14]=[CH:13][C:9]=2[C:10]([OH:12])=O)=[CH:3][CH:2]=1.C(Cl)(Cl)Cl>CO.O.O1CCOCC1>[CH3:20][C:1]1[CH:2]=[C:3]2[C:4]([NH:7][C:8]3[CH:16]=[C:15]([C:17]([OH:19])=[O:18])[CH:14]=[CH:13][C:9]=3[C:10]2=[O:12])=[CH:5][CH:6]=1To a round bottom flask equipped with a condenser was added compound 138A (2.0 g), polyphosphoric acid (15 g) and CHCl3 (50 mL), and the mixture was heated to 100° C. for 18 h. LC/MS indicated that the reaction was complete. The reaction mixture was cooled to room temperature, diluted with MeOH (25 mL), and H2O (50 mL) was added. The resulting mixture was filtered through a medium porosity fritted funnel, washed with MeOH:1% Et3N in H2O (1:1, 30 mL) two times, and dried in air to give a yellow paste which was then dispersed in dioxane (10 mL) with sonication and dried over lyophlyzer to give compound 138B as a yellow solid (2.0 g). HPLC retention time: 2.76 min., condition A. M+: 254.
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