22103
The key intermediate 20 was prepared by a six - step sequence from the corresponding arabinonucleoside by selective protection of 3 ' - and 5 ' - hydroxy groups with acid - labile groups , followed by stereoselective SN 2 fluorination and deprotection .
 Chemical: arabinonucleoside; Chemical: 3 ' - and 5 ' - hydroxy
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: Chemical 
Text: {0} 
Answer:
 Chemical: arabinonucleoside; Chemical: 3 ' - and 5 ' - hydroxy