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: Among several chemoconvulsants , bicuculline , N - methyl - D - aspartic acid and BAY k - 8644 ( the opener of L - type calcium channels ) reversed the protective activity of loreclezole alone and its combination with valproate .
### Output Text:
Among several chemoconvulsants , <span class="chemical">bicuculline</span> , <span class="chemical">N - methyl - D - aspartic acid</span> and <span class="chemical">BAY k - 8644</span> ( the opener of L - type <span class="chemical">calcium</span> channels ) reversed the protective activity of <span class="chemical">loreclezole</span> alone and its combination with <span class="chemical">valproate</span> . 