| Comp. | X | R |
| 4a | -NH | Methyl |
| 4b | -NH | Ethyl |
| 4c | -NH | Isopropyl |
| 4d | -NH | Cyclopropyl |
| 4e | -S | Methyl |
| 4f | -S | Ethyl |
| 4g | -S | Isopropyl |
| 4h | -S | Cyclopropyl |
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