There are 9 words that start with 'isopr'.
| isoprene | isoprenes | 
| isopropyl | isoprenoid | 
| isopropyls | isoprenaline | 
| isoprenalines | isoproterenol | 
| isoproterenols | |
Note: These 9 words that start with 'isopr' are found from the USA & Canada version of the tournament Scrabble word list.