10188
D. R. Appleton et al. / Tetrahedron 57 -2001) 10181±10189
H2O were added and the solvent was removed in vacuo.
Puri®cation was achieved using C18 ¯ash column chromato-
graphy. After eluting with H2O and then MeOH/H2O
#40:60), the product 9 #31 mg, 78%) was eluted with
MeOH/H2O #50:50). The solvent was removed in vacuo
yielding a white amorphous solid. Mp 188±1928C;
anhydrous MgSO4. The solvent was the removed in vacuo
yielding 20 #131 mg, 96%) as a clear glass. [a]20 115# c
D
1.0, MeOH); IR #smear) nmax 3401, 2924, 1738, 1659, 1515,
1435, 1342, 1221, 743 cm21; 1H NMR #CDCl3, 400 MHz) d
8.16, 8.11 #2H, each s, H-1, H-14), 7.61 #1H, d, J7.9 Hz,
H-11), 7.62±7.04 #8H, series of doublets and triplets, H-4,
H-5, H-6, H-7, H-17, H-18, H-19, H-20), 6.93, 6.84 #2H,
each d, J2.2, 2.4 Hz resp, H-2, H-15), 4.92 #1H, m, H-12),
3.66 #3H, s, CO2CH3), 3.64 #1H, m, H-9), 3.32 #1H, dd,
J14.6, 4.5Hz, H-8), 3.27 #2H, d, J5.7 Hz, H-13), 2.84
#1H, dd, J14.6, 9.1 Hz, H-8), #NH2 not observed); 13C
NMR #CDCl3, 100 MHz) d 174.6, 172.4, 136.4, 136.1,
127.6, 127.4, 123.1, 122.7, 122.17, 122.15, 119.6, 119.5,
118.9, 118.6, 111.7, 111.24, 111.20, 110.2, 55.6, 52.6,
52.3, 30.6, 27.6; FABMS m/z 405[M 1H]1; HRFABMS
m/z 405.1935 #calcd for C23H25N4O3 405.1927).
[a]20 26 #c 0.69, MeOH/H2O #1:1)); UV #MeOH) lmax
D
#log 1) 220 #4.72), 274 #3.95), 281 #3.97), 290 #3.90) nm; IR
#smear) nmax 3043, 1668, 1617, 1548, 1202, 1131,
1
745cm 21; H NMR ##CD3)2SO, 400 MHz) d 11.26 #1H,
bs, H-1), 10.83 #1H, bs, H-14), 8.40 #1H, bs, H-11), 7.55
#1H, d, J7.9 Hz, H-4), 7.51 #1H, d, J7.9 Hz, H-17), 7.34
#1H, d, J7.9 Hz, H-7), 7.27 #1H, d, J8.0 Hz, H-20), 7.21
#1H, bs, H-2), 7.11 #1H, bs, H-15), 7.06 #1H, t, J7.7 Hz,
H-6), 7.00 #1H, t, J7.2 Hz, H-5), 7.00 #1H, t, J7.2 Hz,
H-19), 6.91 #1H, t, J7.4 Hz, H-18), 4.49 #1H, bm, H-9),
4.08 #1H, bm, H-12), 3.34 #1H, obsc, H-13), 3.31 #1H, obsc,
H-8), 3.23 #1H, dd, obsc, H-8), 3.08 #1H, dd, J14.8,
5.8 Hz, H-13), 2.88 #9H, s, 1N#CH3)3); 13C NMR
##CD3)2SO, 100 MHz) d 171.7 #CO22), 163.8 #C-10),
136.0 #C-7a), 135.7 #C-20a), 127.8 #C-16a), 126.7 #C-3a),
124.0 #C-2), 123.3 #C-15), 120.9 #C-6), 120.3 #C-19), 118.3
#C-17), 118.2 #C-5), 117.9 #C-4), 117.7 #C-18), 111.5 #C-7),
111.1 #C-16), 110.9 #C-20), 106.6 #C-3), 73.1 #C-9), 55.5
#C-12), 51.0 #1N#CH3)3), 27.1 #C-13), 21.6 #C-8); FABMS
m/z 433 [M1H]1; HRFABMS m/z 433.2253 #calcd for
C25H29N4O3 433.2240).
3.4.10. l-Tryptophyl-d-tryptophan ,21). To a solution of
20 #121 mg, 0.30 mmol) in MeOH #2 mL), KOH #0.56 g,
10 mmol) in H2O #3 mL) was added. The mixture was stir-
red at room temperature for 5h. The resulting mixture was
neutralised with 2N HCl, and the solvent was removed in
vacuo. The product was puri®ed with C18 ¯ash column chro-
matography by eluting with H2O and then with MeOH/H2O
#40:60) to yield 21 #85mg, 73%) as a white amorphous
solid. Mp 184±1888C; [a]20 143 #c 0.89, MeOH); IR
D
#smear) nmax 3400, 3050, 1729, 1673, 1457, 1338, 1230,
1
743 cm21; H NMR ##CD3)2SO, 400 MHz) d 11.01, 10.92
3.4.8. N-t-Butyloxycarbonyl-l-tryptophyl-d-tryptophan-
methyl ester ,19). Compounds 13 #100 mg, 0.39 mmol) and
12 #119 mg, 0.39 mmol) were dissolved in dry CH2Cl2
#10 mL) and dry Et3N #136 mL, 0.98 mmol). To this, BOP
#190 mg, 0.43 mmol) was added and the mixture was stirred
under N2 at room temperature for 4.5h. CH 2Cl2 #20 mL)
was then added and the solution was washed with 2N HCl
#2H, each d, J1.9, 1.8 Hz resp, H-1, H-14), 8.94 #1H, d,
J8.0 Hz, H-11), 7.58±6.79 #8H, series of doublets and
triplets, H-4, H-5, H-6, H-7, H-17, H-18, H-19, H-20),
7.15, 7.10 #2H, each d, J2.3 Hz, H-2, H-15), 4.52 #1H,
m, H-12), 4.01 #1H, dd, J8.3, 5.2 Hz, H-9), 3.15 #1H,
dd, J14.4, 5.2 Hz, H-13), 3.07 #1H, dd, J14.7, 5.1 Hz,
H-8), 3.01 #1H, dd, J14.4, 8.5Hz, H-13), 2.84 #1H, dd,
J14.6, 8.3 Hz, H-8), #NH2 and CO2H not observed); 13C
NMR ##CD3)2SO, 100 MHz) d 173.0, 168.7, 136.2, 136.0,
127.1, 127.0, 124.8, 123.8, 120.9, 120.8, 118.5, 118.3,
118.2, 118.1, 111.3, 111.2, 109.4, 106.9, 53.3, 52.5, 27.5,
27.3; FABMS m/z 391 [M1H]1; HRFABMS m/z 391.1785
#calcd for C22H23N4O3 391.1770).
#1£25mL), H 2O #1£25mL), 5% sat. NaHCO #1£25mL)
3
and brine #1£25mL). It was then dried with anhydrous
MgSO4 and the solvent was removed in vacuo. The product
was puri®ed with silica ¯ash column chromatography elut-
ing with CH2Cl2/MeOH #95:5) yielding 19 #194 mg, 98%)
as a clear glass. [a]20 13 #c 1.0, MeOH); IR #smear) nmax
D
1
3333, 2928, 1704, 1666, 1502, 1366, 1166, 742 cm21; H
NMR #CDCl3, 400 MHz) d 8.06 #2H, bs, H-1, H-14), 7.64±
7.02 #8H, series of doublets and triplets, H-4, H-5, H-6, H-7,
H-17, H-18, H-19, H-20), 6.77, 6.41 #2H, each s, H-2,
H-15), 6.24 #1H, d, J7.7 Hz, H-11), 5.18 #1H, bs,
NHCO2), 4.76 #1H, bm, H-12), 4.43 #1H, bm, H-9), 3.56
#3H, s, CO2CH3), 3.20 #1H, bm, H-8), 3.14±3.09 #2H, m,
3.4.11. N-,N-,N-Trimethylammonium-l-tryptophyl-d-
tryptophan inner salt ,10). To a solution of 21 #40 mg,
0.10 mmol) in MeOH #5mL), MeI #128 mL, 2.0 mmol)
and KHCO3 #102 mg, 1.02 mmol) were added. The mixture
was then stirred at room temperature for 2 d. Two drops of
H2O were added and the solvent was removed in vacuo.
Puri®cation was achieved using C18 ¯ash chromatography.
After eluting with H2O and then MeOH/H2O #40:60), the
product 10 #33 mg, 75%) was eluted with MeOH/H2O
#50:50). The solvent was then removed in vacuo yielding
H-8, H-13), 2.92 #1H, m, H-13), 1.39 #9H, s, OC#CH3)3); 13
C
NMR #CDCl3, 100 MHz) d 172.0, 171.4, 155.4, 136.14,
136.07, 127.5, 127.2, 123.2, 122.9, 122.1, 119.7, 119.5,
118.9, 118.4, 111.2, 110.5, 109.3, 80.0, 55.2, 52.4, 52.3,
28.6, 28.3, 27.3, #plus two carbon resonances either
obscured or not observed); FABMS m/z 505 [M1H]1;
HRFABMS m/z 505.2444 #calcd for C28H33N4O5 505.2451).
a white amorphous solid. Mp 198±2038C; [a]20 15 2 c#
D
0.48, MeOH/H2O #1:1)); UV #MeOH) lmax #log 1) 219
#4.72), 273 #3.96), 281 #3.99), 290 #3.91) nm; IR #smear)
1
nmax 3246, 1671, 1596, 1454, 1385, 1100, 742 cm21; H
3.4.9. l-Tryptophyl-d-tryptophan-methyl ester ,20). To a
solution of 19 #170 mg, 0.34 mmol) in CH2Cl2 #9 mL), TFA
#1 mL) was added. The mixture was then stirred at room
temperature under N2 for 1.5h. The solvent was then
removed in vacuo. The resulting product was dissolved in
CH2Cl2 #20 mL), washed with 5% sat. NaHCO3 #1£25mL),
H2O #1£25mL) and brine #1 £25mL) then dried with
NMR ##CD3)2SO, 400 MHz) d 11.55 #1H, bs, H-1), 11.02
#1H, bs, H-14), 8.42 #1H, d, J7.8 Hz, H-11), 7.57 #1H, d,
J7.9 Hz, H-4), 7.43 #1H, d, J8.1 Hz, H-7), 7.38 #1H, d,
J7.9 Hz, H-17), 7.29 #1H, d, J8.1 Hz, H-20), 7.08 #1H,
bs, H-2), 7.06 #1H, td, J8.1, 0.8 Hz, H-6), 6.99 #1H, t,
J7.3 Hz, H-5), 6.95 #1H, t, J7.3 Hz, H-19), 6.83 #1H, t,
J7.4 Hz, H-18), 6.46 #1H, bs, H-15), 4.55 #1H, dd, J10.3,