Med Chem Res (2013) 22:3918–3933
3923
Synthesis of PCU cage diol diprolinamide (9) A solution
of compound 14 (1 eq, 0.5 g) in 15 mL of dry DCM was
stirred at room temperature for 5 min. To this mixture was
added prolinamide (4 eq, 0.8 g). The solution was cooled
in an ice water bath and stirred for 5 min. To the above-
cooled mixture was added HATU (5 eq, 3.24 g) followed
by DIPEA (8 eq, 1.76 g, 2.4 mL) as a base. The solution
was then slowly brought to room temperature and stirred
for 6 h. The crude reaction mixtures was diluted with DCM
and filtered. The crude product was evaporated to dryness
under vacuum using a Teflon pump at 40 °C to obtain a
thick yellow oil which was purified by preparative HPLC
and solid-phase extraction to give pure PCU cage diol
diprolinamide 9 as pale yellow solid (65 %). Melting point:
83–85 °C. Retention time: 13.42 min (HPLC), [a]2D0:
-37.50 (c 0.16 in MeOD). IR mmax: 3,179, 2,957, 2,872,
1,669, 1,603, 1,448, 1,417, 1,288, 1,191, 1,168, 1,071, 987,
J = 10.6 Hz), 1.47 (1H, d, J = 10.5 Hz), 1.85 (1H, d,
J = 8.4 Hz), 2.02 (1H, d, J = 8.7 Hz), 2.10–2.35 (8H, m),
2.49 (2H, s), 2.86–2.92 (2H, m), 3.14–3.18 (2H, m), 3.71
(1H, s) 4.65–4.67 (1H, q, J = 4.5 Hz), 4.72–4.74 (1H, q,,
J = 4.5 Hz), 6.69–6.73 (4H, m), 7.01–7.06 (4H, m). 13C
NMR [CD3OD, 100 MHz]: dC 34.8, 37.8, 40.5, 40.7, 44.2,
44.5, 45.0, 45.6, 45.7, 45.8, 50.3, 50.5, 52.8, 55.0, 78.3,
78.7, 116.4, 116.5, 128.9, 131.5, 131.6, 157.4, 157.5,
174.0, 174.2. HR ESI m/z: calculated for C33H36N2O10
[M-H]-: 619.2297 found 619.2045.
Synthesis of PCU cage diol diproline (12) A white solid
(35 %). Retention time: 14.34 min (HPLC), Melting point:
170–172 °C, [a]D20: -63.64 (c 0.11 in MeOD). IR mmax
3,164, 2,957, 2,875 1,720, 1,598, 1,448, 1,423, 1,288,
:
1,223, 1,188, 1,072, 978, 908, 873, 654, 544, and
1
429 cm-1. H NMR [CD3OD, 600 MHz]: dH 1.16 (1H, d,
908, 653, 539 and 421 cm-1 1H NMR [(CD3)2SO,
.
J = 10.7 Hz), 1.62 (1H, d, J = 11.2 Hz), 1.98–2.01 (5H,
m), 2.18–2.31 (5H, m), 2.36–2.40 (1H, m), 2.43–2.62 (8H,
m), 2.75–2.83 (1H, m), 3.48–3.56 (1H, m), 3.63–3.73 (3H,
m), 4.41–4.44 (1H, m), 4.71–4.77 (1H, m). 13C NMR
[CD3OD, 100 MHz]: dC 23.6, 23.7, 30.5, 30.6, 32.1, 34.9,
35.0, 40.6, 40.7, 40.8, 40.9, 41.0, 43.1, 43.2, 43.5, 43.7,
44.7, 44.9, 45.8, 45.9, 46.0, 47.5, 51.1, 51.4, 51.6, 52.9,
53.0, 53.4, 60.3, 61.5, 79.4, 79.5, 79.6, 79.7, 173.4, 175.8,
175.9. HR ESI m/z: calculated for C25H32N2O8 [M-H]-:
487.2086 found 487.2025.
400 MHz]: dH 1.04 (1H, t, J = 10.6 Hz), 1.48 (1H, t,
J = 10.5 Hz), 1.74–2.72 (14H, m), 3.50–3.68 (2H, m),
4.16–4.22 (2H, m), 6.92–6.95 (2H, m), 7.08–7.22 (2H, m).
13C NMR [(CD3)2SO, 100 MHz]: dC 24.03, 29.3, 33.5,
38.5, 41.3, 42.0, 42.2, 43.9, 47.3, 50.3, 59.3, 77.8, 170.6,
173.8. HR ESI m/z: calculated for C25H34N4O6 [M?H]?:
487.2542 found 487.2551.
Synthesis of PCU cage diol ditryptophan (10) A pale
white solid (62 %). Retention time: 15.58 min (HPLC),
Melting point: 168–170 °C, [a]2D0: -30.77 (c 0.13 in
MeOD). IR mmax: 3,307, 2,924, 2,855 1,720, 1,624, 1,532,
1,457, 1,429, 1,343, 1,218, 1,190, 1,099, 1,064, 1,010, 910,
Synthesis of PCU cage diol dihistidine (13) A solution of
compound 14 (1 eq, 0.5 g) in 2 mL in dry DMF was stirred
in a microwave reactor vessel. To this above solution was
added H-His(trt)-OMeꢀHCl (2.5 eq, 0.8 g) followed by
HATU (2.5 eq, 3.24 g) and DIPEA (8 eq, 1.76 g, 2.4 mL)
as a base. The solution mixture was then subjected to
microwave irradiation at 200 W for 20 min at 55 °C and
then 300 W for 20 min at 60 °C (Santagada et al., 2001).
The resulting solution was diluted in an excess of water
(50 mL) and extracted twice with ethyl acetate
(2 9 50 mL). The organic layer was then washed with
brine (2 9 50 mL), dried over anhydrous Na2SO4 and fil-
tered. The crude product 24 was concentrated in vacuo to
obtain a thick colourless oil. This crude product 24 was
dissolved in a solution of TFA and water (3:1) and stirred
at 60 °C for 8 h. Excess of TFA and water from the crude
reaction mixture was removed in vacuo to give a pale
yellow oil, which was purified by preparative HPLC to give
pure PCU cage diol dihistidine 13 as a colourless oil
(58 %). Retention time: 09.80 min (HPLC), [a]2D0: =?6.25
(c 0.12 in MeOD). IR mmax: 3,132, 2,956, 2,862, 1,965,
1,624, 1,577, 1,434, 1,389, 1,289, 1,258, 1,187, 1,133,
821, 740, 536 and 424 cm-1
.
1H NMR [DMSO,
600 MHz]: dH 0.96 (1H, d, J = 10.3 Hz), 1.23 (1H,s), 1.32
(1H, d, J = 10.1 Hz), 1.88 (1H, d, J = 8.9 Hz), 1.95 (1H,
d, J = 8.8 Hz), 2.05–2.12 (2H, m), 2.19–2.22 (3H, m),
2.28–2.29 (3H, m), 2.37–2.43 (2H, m), 3.03–3.08 (2H,m),
3.16–3.28 (2H,m), 4.52–4.60 (2H, m), 6.94–7.06 (4H, m,),
7.12 (2H, q, J = 2.1 Hz), 7.32 (2H, t, J = 7.5 Hz), 7.42
(2H, s), 7.52 (2H, q, J = 4.1 Hz), 8.08 (1H, d,
J = 7.6 Hz), 8.19 (1H, d, J = 7.6 Hz), 10.81 (1H, d,
J = 1.3 Hz), 10.86 (1H, d, J = 1.8 Hz), 12.69 (1H,s). 13C
NMR [CD3OD, 100 MHz]: dC 27.1, 33.3, 38.7, 42.3, 43.6,
43.9, 44.1, 48.7, 48.8, 52.5, 64.8, 76.6, 76.7, 109.3, 111.3,
118.1, 118.3, 120.8, 123.5,123.7, 127.1, 127.2, 136.0,
171.1, 171.2, 173.1. HR ESI m/z: calculated for
C37H38N4O8 [M-H]-: 665.2617 found 665.2497.
Synthesis of PCU cage diol dityrosine (11) A white solid
(32 %). Retention time: 14.23 min (HPLC), Melting point:
199–201 °C, [a]D20: ?23.08 (c 0.13 in MeOD). IR mmax
3,232, 2,954, 2,865 1,721, 1,614, 1,536, 1,514, 1,441,
:
1
1,066, 984, 831, 797, 627, 542, and 435 cm-1. H NMR
1,364, 1,221, 1,105, 1,064, 986, 910, 825, 530 and
1
[(CD3)2SO, 600 MHz]: dH 0.97 (1H, d, J = 10.0 Hz), 1.38
(1H, d, J = 10.1 Hz), 1.90 (1H, d, J = 08.1 Hz),
428 cm-1. H NMR [CD3OD, 600 MHz]: dH 1.05 (1H, d,
123