| Compound | [α]D25 in MeOH | Tautomeric composition in D2O, (%) | ||
| Form A | Form (2R,4S) | Form (2S,4S) | ||
| 2a | ?89.1, с 1.31 | ? | 95 | 5 |
| 2b | ?91.2, с 1.50 | ? | 93 | 7 |
| 2c | ?70.1, с 1.50 | ? | 90 | 10 |
| 2d | ?97.7, с 1.40 | ? | 93 | 7 |
| 2e | ?77.2, с 1.53 | ? | 87 | 13 |
| 2f | ?69.5, с 1.50 | ? | 92 | 8 |
| 2g | ?60.2, с 2.01 | 13 | 68 | 19 |
| 2h | ?35.1, с 2.02 | 51 | 40 | 9 |
| 2i | ?37.2, с 1.70 | 18 | 66 | 16 |