[NH2:1][C@H:2]([C:5]([OH:7])=[O:6])[CH2:3][SH:4].[CH:8]1[C:21]2[CH:20](O)[C:19]3[C:14](=[CH:15][CH:16]=[CH:17][CH:18]=3)[O:13][C:12]=2[CH:11]=[CH:10][CH:9]=1.C([O-])([O-])=O.[Na+].[Na+]>COCCOC.C(O)(C(F)(F)F)=O>[CH:8]1[C:21]2[CH:20]([S:4][CH2:3][C@@H:2]([C:5]([OH:7])=[O:6])[NH2:1])[C:19]3[C:14](=[CH:15][CH:16]=[CH:17][CH:18]=3)[O:13][C:12]=2[CH:11]=[CH:10][CH:9]=1A sample of 0.61 g of cysteine (5 mmole) was suspended in 100 ml of 1,2-dimethoxyethane and 2 ml of TFA. The suspension was stirred under nitrogen gas at room temperature until the solution became clear. To this clear solution was added 1 g of 9H-xanthen-9-ol (5.1 mmole) in one portion. The reaction mixture was stirred at room temperature for 30 minutes and was then neutralized to pH 7 by the addition of a saturated aqueous Na2CO3 solution. The mixture was then concentrated by rotary evaporation. The residue was diluted with 50 ml of water. The aqueous solution was treated with 10% aqueous citric acid solution to adjust the pH to 6. The mixture was stirred at room temperature for 1 hr. The resultant white solid was collected by filtration and was washed with 3×10 ml of water and 3×10 ml of ethyl acetate. The product was dried to yield 1.30 g of product.
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