反应详情

Methyl pheophorbide-a (2) prepared in Example 1 (300 mg, 0.49 mmole) was dissolved in warm pyridine (5 mL) and the solution was diluted with ether (500 mL). The solution was stirred with a stream of air passing through it, and a solution of potassium hydroxide (4 g) in n-propanol (10 mL) was added. The bright green mixture containing precipitated potassium hydroxide was stirred and aerated for 30 min and then extracted with wateruntil the ethereal layer was no longer green. The ethereal solution was discarded, the aqueous extracts were combined and adjusted to pH~4 with concentrated sulfuric acid (~4 mL). Then the mixture was extracted with methylene chloride until the aqueous layer was no longer green-brown. The combined methylene chloride extract containing so-called "unstable chlorin" was subjected to repeated evaporation and redissolutionin distilled THF until no further increase in visible absorption at 700 nm was observed. The product was esterified with ethereal diazomethane, then washed with water, dried and evaporated to dryness. The product was purified on preparative TLC plates, eluting with 2% methanol in methylene chloride to give a purple-brown band. After evaporating the solvents, the residue was crystallized from methylene chloride/methanol to yield 143 mg (50%) of purpurin-18 methyl ester (3).

1. additionThe bright green mixture containing
2. customprecipitated potassium hydroxide
3. stirringwas stirred
4. extractionextracted with wateruntil the ethereal layer
5. extractionThen the mixture was extracted with methylene chloride until the aqueous layer
6. extractionThe combined methylene chloride extract
7. additioncontaining so-called "unstable chlorin"
8. customevaporation and redissolutionin
9. distillationdistilled THF until
10. temperatureno further increase in visible absorption at 700 nm
11. washwashed with water
12. customdried
13. customevaporated to dryness
14. customThe product was purified on preparative TLC plates
15. washeluting with 2% methanol in methylene chloride
16. customto give a purple-brown band
17. customAfter evaporating the solvents
18. customthe residue was crystallized from methylene chloride/methanol