9969
Attempts to block metabolism by incorporating a 9 - fluoro substituent at the A - ring of compound 1 ( SCH 900229 ) using electrophilic Selectfluor (TM) led to an unexpected oxidation of the A - ring to give difluoroquinone analog 1a .
 9 - fluoro, SCH 900229, Selectfluor, difluoroquinone
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 9 - fluoro, SCH 900229, Selectfluor, difluoroquinone