In the sentence extracted from biomedical literature, identify all the chemical entities. The required answer format is the same sentence with HTML <span> tags to mark up specific entities. 
### Entity Markup Guides:
Use <span class="chemical"> to denote a chemical.

### Input Text: Of the CCK - 2 - 8 analogues , Ser ( SO3H ) 7 - Ac - CCK - 2 - 8 - SE and Thr ( SO3H ) 7 - Ac - CCK - 2 - 8 - SE and Hyp ( SO3H ) - Ac - CCK - 2 - 8 - SE were slightly more active than CCK - 8 - SE .
### Output Text:
Of the CCK - 2 - 8 analogues , Ser ( SO3H ) 7 - Ac - CCK - 2 - 8 - SE and Thr ( SO3H ) 7 - Ac - CCK - 2 - 8 - SE and Hyp ( SO3H ) - Ac - CCK - 2 - 8 - SE were slightly more active than <span class="chemical">CCK - 8</span> - SE . 