Table 1.
1H NMR data of compounds 1–7 (1–6 recorded in CDCl3, 7 recorded in CD3OD, δH in ppm, J in Hz).
| Position | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|
| L-Phenylalanine | L-Tyrosine | ||||||
|
| |||||||
| α | 4.63–4.67, m | 4.63, dd (2.5, 10.5) | 4.69–4.77, m | 4.65, dd (3.4, 11.4) | 4.61, dd (3.0, 11.0) | 4.61–4.67, m | 4.52, dd (6.2, 8.3) |
| α-NH | - | - | 6.54, d (8.6) | - | - | 6.8, d (8.3) | N/A |
| N-CH3 | 2.87, s | 2.87, s | - | 2.87, s | 2.87, s | - | - |
| β | 2.94 dd (10.5, 14.4) 3.38, dd (2.7, 14.3) |
2.95, dd (10.9, 12.4) 3.30, dd (2.52, 12.2) |
3.12–3.23, m | 2.94, dd (11.7, 14.4) 3.41, dd (3.4, 14.1) |
2.88, dd (11.5, 14.5) 3.31, dd (3.0, 14.5) |
3.05–3.10, m | 2.99 dd (8.6, 14.1) 3.12, dd (6.2, 14.1) |
| o | 7.10, d (7.5) | 7.07, d (6.9) | 7.17, d (7.1) | 7.09, d (6.9) | 6.91, d (8.5) | 6.96, d (7.9) | 6.99, d (8.6) |
| m | 7.26–7.31, m | 7.23–7.29, m | 7.23–7.32, m | 7.22–7.31, m | 6.75, d (8.5) | 6.74, d (7.9) | 6.99, d (8.6) |
| p | 7.23–7.25, m | 7.23, t (6.9) | 7.23, t (6.9) | 7.29, t (7.6) | - | - | - |
|
| |||||||
| β-Alanine | R-3-Aminoisobutyric acid (R-3-AIB) | β-Alanine | |||||
|
| |||||||
| α | 2.54–2.61, m | 2.64–2.69, m | 2.53–2.67, m | 2.57, dd (3.8, 8.3) | 2.54–2.57, m | 2.49–2.52, m | 2.44–2.59, m |
| α-CH3 | - | 1.21, d (7.1) | - | - | - | - | - |
| β | 3.31–3.39, m 3.98–4.09, m |
3.60–3.71, m | 3.82–3.94, m 3.25–3.34, m |
4.04, dt (3.8, 13.7) 3.33–3.42, m |
3.97–4.10, m 3.34–3.42, m |
3.80–3.84, m 3.21–3.25, m |
3.73–3.80, m 3.22–3.30, m |
| β-NH | 7.45–7.48, m | 7.45, dd (5.0, 5.5) | 7.10–7.15, m | 7.44–7.49, m | 7.49, d (6.8) | 7.55–7.57, m | N/A |
|
| |||||||
| (R)-2-hydroxyisocaproic acid (R-HICA) | |||||||
|
| |||||||
| α | 5.13–5.18, m | 5.12, dd (5.0, 7.6) | 5.19, dd (3.8, 9.9) | 5.21, dd (6.2, 7.9) | 5.17, dd (6.4, 7.6) | 5.17–5.21, m | 5.17–5.24, m |
| β | 1.68–1.85, m | 1.68–1.88, m | 1.66–1.90, m | 1.72–1.87, m | 1.71–1.85, m | 1.62–1.83, m | 1.61–1.78, m |
| γ | 1.59–1.71, m | 1.58–1.73, m | 1.60–1.77, m | 1.59–1.70, m | 1.60–1.69, m | 1.54–1.68, m | 1.64–1.74, m |
|
| |||||||
| L-Leucine | L-Valine | L-Leucine | L-Valine | ||||
|
| |||||||
| α | 4.48–4.56, m | 4.50, ddd (3.0, 9.7, 10.8) | 4.08–4.18, m | 4.43, d (4.1) | 4.48–4.55, m | 4.13–4.17, m | 3.90, d (8.9) |
| α-NH | 6.16, d (9.8) | 6.32, d (9.4) | 6.89, d (6.6) | 6.41, d (9.6) | 6.32, d (9.6) | 7.41, d (6.6) | N/A |
| β | 1.57–1.72, m | 1.48–1.73, m | 1.54–1.73, m | 2.35, qqd (4.1, 6.5, 6.9) | 1.50–1.81, m | 1.50–1.70, m | 2.08–2.16, m |
| γ | 1.65–1.86, m | 1.61–1.76, m | 1.60–1.77, m | 1.64–1.82, m | 1.54–1.65, m | ||
|
| |||||||
| (S)-2-Hydroxyisocaproic acid (S-HICA) | |||||||
|
| |||||||
| α | 4.65–4.70, m | 4.73, dd (2.1, 10.5) | 5.07, dd (3.6, 6.1) | 4.66, dd (2.3, 11.3) | 4.72, dd (1.8, 11.0) | 5.15–5.17, m | 5.17–5.24, m |
| β | 1.35–1.59, m −0.38 – −0.47, m |
1.36–1.48, m −0.32 – −0.40, m |
1.35–1.54, m | 1.37–1.52, m −0.38 – −0.47, m |
1.41–1.50, m −0.21 – −0.27, m |
1.45–1.57, m | 1.29–1.54, m |
| γ | 1.35–1.59, m | 1.36–1.48, m | 1.33–1.52, m | 1.23–1.40, m | 1.43–1.60, m | 1.30–1.43, m | 1.43–1.49, m |
|
| |||||||
| R/S-2-Hydroxyisocaproic acid (R/S-HICA) and δ-H of L-leucine (L-Leu)/γ-H of L-valine (L-Val) | |||||||
|
| |||||||
|
R-HICA 0.56, d (6.5) 0.67, d (6.5) S-HICA/L-Leu 0.89, d (6.5) 0.93, d (6.5) |
R-HICA/L-Leu 0.92, d (5.5) 0.87, d (5.9) S-HICA 0.66, d (6.2) 0.56, d (6.4) |
S-HICA 0.84, d (5.9) 0.86, d (6.8) R-HICA/L-Leu 0.92, d (6.2) 0.93, d (6.2) 0.95, d (6.5) 1.00, d (5.9) |
R-HICA 0.91, d (6.5) 0.95, d (6.1) L-Val 0.91, d (6.5) 1.01, d (6.9) S-HICA 0.56, d (6.5) 0.67, d (6.5) |
R-HICA/L-Leu 0.90, d (6.2) 0.9, d (6.4) S-HICA 0.62, d (6.4) 0.73, d (6.2) |
S-HICA 0.91, d (5.9) 0.92, d (6.2) L-Leu 0.91, d (5.9) 0.97, d (5.5) R-HICA 0.83, d (5.8) 0.87, d (5.2) |
R-HICA 0.95, d (6.5) 0.99, d (6.2) L-Val 0.97, d (6.5) 1.00, d (6.5) S-HICA 0.86, d (5.8) 0.89, d (5.8) |
|