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: S - 312 , S - 312 - d , but not S - 312 - l , L - type calcium channel antagonists , showed anticonvulsant effects on the audiogenic tonic convulsions in DBA / 2 mice ; and their ED50 values were 18 . 4 ( 12 . 8 - 27 . 1 ) mg / kg , p . o . and 15 . 0 ( 10 . 2 - 23 . 7 ) mg / kg , p . o . , respectively , while that of flunarizine was 34 . 0 ( 26 . 0 - 44 . 8 ) mg / kg , p . o .
### Output Text:
<span class="chemical">S - 312</span> , <span class="chemical">S - 312 - d</span> , but not <span class="chemical">S - 312 - l</span> , L - type <span class="chemical">calcium</span> channel antagonists , showed anticonvulsant effects on the audiogenic tonic convulsions in DBA / 2 mice ; and their ED50 values were 18 . 4 ( 12 . 8 - 27 . 1 ) mg / kg , p . o . and 15 . 0 ( 10 . 2 - 23 . 7 ) mg / kg , p . o . , respectively , while that of <span class="chemical">flunarizine</span> was 34 . 0 ( 26 . 0 - 44 . 8 ) mg / kg , p . o . 