Baeza et al.
JOCArticle
purified by flash chromatography or centrifugal circular thin-
layer chromatography, using the system of eluents indicated in
each case.
(CH3-NH), 22.7 (3-C), 18.3 (β-C, Ala). ES-MS: 410.2 [M þ 1]þ,
432.1 [M þ Na]þ. Anal. Calcd for C23H27N3O4: C, 67.46; H,
6.65; N, 10.26. Found: C, 67.21; H, 6.81; N, 10.18.
Method B. To a solution of the corresponding dipeptide with
the free C-terminal carboxylic acid (0.34 mmol) in CH2Cl2 were
added MeNH2 HCl (3.40 mmol) and BOP (195 mg, 0.44 mmol).
The solution was cooled to 0 °C, and TEA (3.84 mmol) was
added. After stirring for 6 days at room temperature, the
reaction mixture was successively washed with citric acid
(10%), NaHCO3 (10%), H2O, and brine. The organic layer
was dried over Na2SO4, the solvent was evaporated to dryness,
and the residue was purified by flash chromatography using the
system of eluents indicated in each case.
General Procedure for the N-Acylation of Dipeptide Deriva-
tives. Method A. To a solution of the corresponding Z-pro-
tected dipeptide (0.73 mmol) in MeOH (15 mL) at 0 °C was
added Pd-C (15% w/w). The mixture was hydrogenated at
15 psi and room temperature for 1 h. After filtration of the
catalyst, the solvent was evaporated to dryness. The residue was
dissolved in dry CH2Cl2 (6 mL) and cooled to 0 °C under argon
atmosphere. Subsequently, TEA (0.21 mL, 1.53 mmol) and
acetyl or pivaloyl chloride (1.17 mmol) were added. After 2 h
of reaction at room temperature the reaction was successively
washed with citric acid (10%), NaHCO3 (10%), H2O, and brine.
The organic layer was dried over Na2SO4, the solvent was
evaporated to dryness, and the residue was purified by flash
chromatography using the system of eluents indicated in each
case.
Method B. Following the same procedure as in Method A,
except that, because of the solubility of the final product in H2O,
the aqueous phase was evaporated to dryness and the resulting
residue was purified by flash chromatography.
Method C. As in Method A, but using propylene oxide
(0.77 mL, 10.92 mmol) instead of TEA. After 15 h of stirring
at room temperature the solvent was evaporated to dryness, and
the residue was purified by flash chromathography using the
system of eluents indicated in each case.
Ac-Ala-Aze-NHMe (11a). Syrup, 80% yield (from 8a, Method
B). Eluent:MeOH/CH2Cl2 (1:20). [R]D =-158.1 (c1.13, CHCl3).
1H NMR (CDCl3): trans/cis isomers ratio 3.5:1; trans isomer δ
7.31 (br s, 1H, NH-CH3), 6.30 (m, 1H, NH-Ala), 4.84 (dd, 1H,
J = 9.4, 6.2, H-2), 4.50 (q, 1H, J = 7.0, R-H, Ala), 4.31 (m, 1H,
H-4), 4.08 (m, 1H, H-4), 2.80 (d, 3H, J = 4.7, CH3-NH), 2.70 (m,
1H, H-3), 2.47 (m, 1H, H-3), 1.99 (s, 3H, CH3-CO), 1.30 (d, 3H,
J = 7.0, β-H, Ala); cis isomer δ 8.21 (br s, 1H, NH-CH3), 6.49 (m,
1H, NH-Ala), 4.75 (dd, 1H, J = 10.2, 5.3, H-2), 4.01 (m, 3H, H-4,
R-H, Ala), 2.89 (d, 3H, J = 4.7, CH3-NH), 2.70 (m, 1H, H-3), 2.34
(m, 1H, H-3), 1.99 (s, 3H, CH3-CO), 1.30 (m, 3H, β-H, Ala). 1H
NMR (400 MHz, DMSO-d6): trans/cis isomers ratio 2.7:1; trans
isomer δ 8.17 (d, 1H, J = 6.8, NH-Ala), 7.86 (m, 1H, NH-CH3),
4.59 (dd, 1H, J = 8.8, 5.9, H-2), 4.32 (q, 1H, J = 6.8, R-H, Ala),
4.27 (m, 1H, H-4), 4.17 (m, 1H, H-4), 2.69 (d, 3H, J = 4.9, CH3-
NH), 2.49 (m, 1H, H-3), 2.16 (m, 1H, H-3), 1.90 (s, 3H, CH3-CO),
1.24 (d, 3H, J = 6.8, β-H, Ala); cis isomer δ 8.37 (m, 1H, NH-
CH3), 8.17 (m, 1H, NH-Ala), 4.85 (dd, 1H, J = 8.8, 3.9, H-2), 4.13
(m, 1H, R-H, Ala), 3.87 (m, 2H, H-4), 2.74 (d, 3H, J = 3.9,
CH3-NH), 2.64 (m, 1H, H-3), 2.16 (m, 1H, H-3), 1.90 (s, 3H,
CH3-CO), 1.24 (m, 3H, β-H, Ala). 13C NMR (CDCl3): trans
isomer δ 174.5 (CO-Ala), 170.9 (2-CO), 169.7 (CO-CH3), 61.9 (2-
C), 48.8 (4-C), 44.4 (R-C, Ala), 26.1 (CH3-NH), 22.8 (CH3-CO),
18.8 (3-C), 17.9 (β-C, Ala); cis isomer δ 173.1 (CO-Ala), 171.5
(CO-CH3), 170.6 (2-CO), 63.0 (2-C), 46.3 (4-C), 46.1 (R-C, Ala),
26.2 (CH3-NH), 22.3 (CH3-CO), 22.2 (3-C), 16.1 (β-C, Ala).
ES-MS: 228.1 [M þ 1]þ, 250.1 [M þ Na]þ. Anal. Calcd for
C10H17N3O3: C, 52.85; H, 7.54; N, 18.49. Found: C, 52.71; H,
7.63; N, 18.29.
3
Z-Ala-2(R,S)-MeAze-NHMe (8b). Syrup, 99% yield [from
(R,S)-4b, Method A]. Eluent: EtAcO/hexane (8:1). HPLC
(Chiralpak, hexane/methanol = 95:5): tR = 22.9 min (major
diastereoisomer), 30.5 min (minor diastereoisomer). Diastereo-
isomers ratio 1.2:1. 1H NMR (CDCl3): major diastereoisomer δ
7.87 (m, 1H, NH-CH3), 7.35 (m, 5H, Ph), 5.42 (m, 1H, NH-Ala),
5.10 (s, 2H, CH2-Z), 4.21 (q, 1H, J = 7.1, R-H, Ala), 4.17 (m,
1H, H-4), 3.97 (m, 1H, H-4), 2.88 (m, 1H, H-3), 2.79 (d, 3H, J =
4.7, CH3-NH), 2.12 (m, 1H, H-3), 1.72 (s, 3H, 2-CH3, 2-
MeAze), 1.30 (d, 3H, J = 7.1, β-H, Ala); minor diastereoisomer
δ 7.93 (m, 1H, NH-CH3), 7.35 (m, 5H, Ph), 5.42 (m, 1H, NH-
Ala), 5.10 (s, 2H, CH2-Z), 4.17 (m, 1H, H-4), 4.13 (q, 1H, J =
7.0, R-H, Ala), 3.97 (m, 1H, H-4), 2.88 (m, 1H, H-3), 2.80 (d, 3H,
J = 4.5, CH3-NH), 2.12 (m, 1H, H-3), 1.73 (s, 3H, 2-CH3, 2-
MeAze), 1.34 (d, 3H, J = 7.0, β-H, Ala). 1H NMR (DMSO-d6):
major diastereoisomer δ 7.75 (m, 1H, NH-CH3), 7.59 (d, 1H,
J = 7.0, NH-Ala), 7.33 (m, 5H, Ph), 5.00 (s, 2H, CH2-Z), 4.15
(m, 1H, H-4), 4.00 (m, 1H, H-4), 3.96 (q, 1H, J = 7.0, R-H, Ala),
2.60 (d, 3H, J = 4.3, CH3-NH), 2.26 (m, 1H, H-3), 2.01 (m, 1H,
H-3), 1.52 (s, 3H, 2-CH3, 2-MeAze), 1.14 (d, 3H, J = 7.0, β-H,
Ala); minor diastereoisomer δ 7.67-7.65 (m, 2H, NH-CH3,
NH-Ala), 7.33 (m, 5H, Ph), 5.02 (s, 2H, CH2-Z), 4.15 (m, 1H, H-
4), 4.00 (m, 1H, H-4), 3.96 (q, 1H, J = 7.0, R-H, Ala), 2.57 (d,
3H, J= 4.3, CH3-NH), 2.26 (m, 1H, H-3), 2.01 (m, 1H, H-3),
1.52 (s, 3H, 2-CH3, 2-MeAze), 1.15 (d, 3H, J = 7.0, β-H, Ala).
13C NMR (CDCl3): major diastereoisomer δ 174.4 (CO-Ala),
172.6 (2-CO), 155.6 (CO-Z), 136.2 (C-Ph), 128.5, 128.2, 128.0
(CH-Ph), 72.0 (2-C), 66.9 (CH2-Z), 46.5 (R-C, Ala), 45.8 (4-C),
27.0 (3-C), 26.2 (CH3-NH), 23.4 (2-CH3, 2-MeAze), 18.2 (β-C,
Ala); minor diastereoisomer δ 174.0 (CO-Ala), 173.4 (2-CO),
155.6 (CO-Z), 136.2 (C-Ph), 128.5, 128.2, 128.0 (CH-Ph), 71.7
(2-C), 66.9 (CH2-Z), 46.7 (R-C, Ala), 45.7 (4-C), 27.4 (3-C), 26.2
(CH3-NH), 23.2 (2-CH3, 2-MeAze), 17.7 (β-C, Ala). ES-MS:
334.0 [M þ 1]þ, 356.0 [M þ Na]þ. Anal. Calcd for C17H23N3O4:
C, 61.25; H, 6.95; N, 12.60. Found: C, 61.00; H, 6.71; N, 12.74.
Z-Ala-2(S)-BnAze-NHMe (8c). Foam, 59% yield [from (S)-
6c, Method B]. HPLC: tR = 13.41 min (Novapak, A:B =
30:70). [R]D = þ30.2 (c 0.35, CHCl3). 1H NMR (CDCl3):
trans/cis isomers ratio 10:1; trans isomer δ 8.09 (c, 1H, J =
4.8, NH-CH3), 7.33-7.07 (m, 10H, Ph), 5.44 (d, 1H, J = 8.3,
NH-Ala), 5.07 (m, 2H, CH2-Z), 4.04 (m, 1H, R-H, Ala), 3.54 (m,
1H, H-4), 3.50 (d, 1H, J = 13.9, 2-CH2, 2-BnAze), 3.07 (m, 1H,
H-4), 2.87 (d, 1H, J = 13.9, 2-CH2, 2-BnAze), 2.78 (d, 3H, J =
4.8, CH3-NH), 2.67 (m, 1H, H-3), 2.15 (m, 1H, H-3), 1.20 (d, 3H,
J = 6.9, β-H, Ala). 1H NMR (400 MHz, DMSO-d6): trans/cis
isomers ratio 10:1; trans isomer δ 7.98 (c, 1H, J = 4.5, NH-
CH3), 7.61 (d, 1H, J = 7.6, NH-Ala), 7.36-7.20 (m, 10H, Ph),
5.04 (m, 2H, CH2-Z), 3.99 (m, 1H, R-H, Ala), 3.76 (m, 1H, H-4),
3.38 (d, 1H, J = 13.9, 2-CH2, 2-BnAze), 3.21 (m, 1H, H-4), 2.98
(d, 1H, J = 13.9, 2-CH2, 2-BnAze), 2.67 (d, 3H, J = 4.5, CH3-
NH), 2.24 (m, 1H, H-3), 2.00 (m, 1H, H-3), 1.16 (d, 3H, J = 6.9,
β-H, Ala). 13C NMR (CDCl3): trans isomer δ 174.1 and 173.8
(CO-Ala and 2-CO), 155.3 (CO-Z), 136.3, 134.6 (C-Ph), 130.3,
128.6, 128.5, 128.2, 128.1, 127.3 (CH-Ph), 75.6 (2-C), 66.9 (CH2-
Z), 46.6 (R-C, Ala), 46.1 (4-C), 39.5 (2-CH2, 2-BnAze), 26.3
Ac-Ala-2(S)-BnAze-NHMe (11c). Syrup, 60% yield (from 8c,
Method C). Eluent: acetone/EtAcO (1:2). HPLC: tR = 3.25 min
1
(Novapak, A:B = 20:80). H NMR (CDCl3): δ 8.14 (m, 1H,
NH-CH3), 7.24 (m, 5H, Ph), 7.22 (d, 1H, J = 6.9, NH-Ala), 4.35
(q, 1H, J = 6.9, R-H, Ala), 3.63 (ddd, 1H, J = 9.8, 8.5, 4.9, H-4),
3.56 (d, 1H, J = 13.9, 2-CH2, 2-BnAze), 3.17 (m, 1H, H-4), 2.97
(d, 1H, J = 13.9, 2-CH2, 2-BnAze), 2.86 (d, 3H, J = 4.7, CH3-
NH), 2.73 (ddd, 1H, J = 12.2, 9.8, 7.2, H-3), 2.23 (ddd, 1H, J =
12.2, 9.2, 4.9, H-3), 2.05 (s, 3H, CH3-CO), 1.26 (d, 3H, J = 6.9,
β-H, Ala). 1H NMR (DMSO-d6): δ 8.18 (d, 1H, J = 7.3, NH-
Ala), 8.04 (m, 1H, NH-CH3), 7.25 (m, 5H, Ph), 4.19 (q, 1H, J =
7.3, R-H, Ala), 3.78 (m, 1H, H-4), 3.37 (d, 1H, J = 13.8, 2-CH2,
8210 J. Org. Chem. Vol. 74, No. 21, 2009