A sample of 1.0 g of S-(9H-Xanthen-9-yl)cysteine (3.3 mmole) from Example 4 was dissolved in 10 ml of chloroform. To the solution was added 1.5 ml of water and 1.5 ml of diethylamine. The mixture was cooled to 4° C. by an ice bath and 0.98 g of trityl chloride (3.5 mmole) was added in portions over a period of 30 min. After 2 h of stirring at room temperature. The reaction mixture was separated. The organic phase was washed twice with 4% diethylamine aqueous solution. The organic layer was dried over Na2SO4. The drying reagent was removed by filtration and the filtrate was condensed to dryness by rotary evaporation. The residue was refluxed in 10 ml of a 1:30 mixture of diethyl amine/ethyl alcohol. The resultant diethyl ammonium salt was partitioned between 10 ml of ethyl acetate and 7 ml of 5% aqueous KHSO4 and 7 ml of water. The ethyl acetate layer was separated and was dried over MgSO4 and was concentrated to get 1.4 g of product.
