Semisynthetic Maytansine Analogues
Journal of Medicinal Chemistry, 2006, Vol. 49, No. 14 4403
5.88 (1H, dd, J ) 9 Hz), 6.22-6.26 (2H, m), 6.41 (1H, dd, J )
11, 15 Hz), 6.78 (1H, d, J ) 1.6 Hz), 6.84 (1H, d, J ) 1.6 Hz).
HRMS calcd for C36H51ClN3O10S2 (M + Na)+, 806.2524; found,
806.2518.
6.820 (1H, d, J ) 2 Hz). HRMS calcd for C37H52ClN3O10S2Na
(M + Na)+, 820.2680; found, 820.2667.
1
6d. H NMR (CDCl3) δ 0.874 (3H, s), 1.193-1.429 (3H, m),
1.290 (3H, d, J ) 6.4 Hz), 1.314 (3H, d, J ) 6.8 Hz), 1.696 (3H,
s), 1.777 (1H, d, J ) 13.6 Hz), 2.058 (2H, m), 2.209 (1H, dd, J )
11.2, 3.2 Hz), 2.420 (3H, s), 2.529 (2H, m), 2.662 (1H, dd, J )
12, 3.6 Hz), 2.727-2.801 (2H, m), 2.826 (1H, d, J ) 9.6 Hz),
3.044 (3H, s), 3.167 (3H, s), 3.204 (1H, d, J ) 11.2 Hz), 3.342
(3H, s), 3.439 (1H, d, J ) 9.2 Hz), 3.514 (1H, d, J ) 7.6 Hz),
3.999 (3H, s), 4.351 (1H, t), 4.933 (1H, dd, J ) 8.8, 3.2 Hz), 5.082
(1H, m), 5.844 (1H, dd, J ) 9.6, 5.6 Hz), 6.231 (1H, d, J ) 8.8
Hz), 6.242 (1H, s), 6.434 (1H, dd, J ) 11.2, 4.4 Hz), 6.799 (1H,
d, J ) 2 Hz) and 6.851 (1H, d, J ) 2 Hz). HRMS calcd for C37H52-
ClN3O10S2Na (M + Na)+, 820.2680; found, 820.2658.
N2′-Deacetyl-N2′-[2-(phenydithio)-1-oxopropyl]maytansine
(DMISPh, 2c) and Its D-Alanyl Isomer D-DM1SPh (6c). May-
tansinol (4) was reacted with N-methyl-N-[(2-phenyldithio)-1-oxo-
proyl]-L-alanine (5c) as described above. The product was purified
by preparative TLC of the residue on silica gel, and eluting twice
with 5% MeOH/CHCL3 gave two strongly UV absorbing bands
with Rf ) 0.5 and 0.6. The two products were isolated by extraction
with ethyl acetate. The higher Rf band was found to be the
D-aminoacyl ester 6c of maytansinol, and the lower band was the
L-aminoacyl ester 2c. The products were separated and further
purified by HPLC on a Waters Radialpak C-18 column, eluting at
a flow rate of 1.5 mL/min with a linear gradient of acetonitrile/
water (70-90% acetonitrile/10 min). Under these conditions, both
isomers had an identical retention time of 6.0 min.
N2′-Deacetyl-N2′-[4-(R,S)-(methyldithio)-1-oxopentyl]may-
tansine (DM3-SMe, 2f). Maytansinol (4) was reacted with N-meth-
yl-N-[(4-(R,S)-methyldithio-1-oxopentyl)]-S-alanine (5f) as de-
scribed above. The reaction mixture was purified by silica
chromatography using a mixture of dichloromethane and methanol
to remove unreacted maytansinol. The fractions containing the
desired product were combined, and the solvent was removed under
vacuum to give a mixture of the diastereomers 2f and 6f. The
residue was purified on a 50 cm × 250 cm, 10 micron Diazem CN
column using as mobile phase a 68:8:24 mixture of hexane,
2-propanol, and ethyl acetate. The flow rate was 118 mL/min. The
desired product 2f eluted with a retention time of 11 min, and the
undesired diastereomer 6f had a retention time of 19 min.
DM1SPh (2c). 1H NMR (CDCl3) δ 0.82 (3H, s), 1.11-1.25 (1H,
m), 1.33 (3H, d, J ) 3 Hz), 1.61 (3H, s), 1.63 (3H, d, J ) 14 Hz),
2.19 (1H, dd, J ) 3, 15 Hz), 2.61 (1H, dd, J ) 12, 15 Hz), 2.78
(3H, s), 2.68-3.03 (2H, m), 3.07 (1H, d, J ) 9 Hz), 3.20 (3H, s),
3.38 (3H, s), 3.53 (1H, d, J ) 9 Hz), 3.63 (1H, d, J ) 13 Hz), 3.68
(3H, s), 4.01 (3H, s), 4.30 (1H, t, J ) 11 Hz), 4.79 (1H, dd, J )
3, 8 Hz), 5.43 (1H, q, J ) 7 Hz), 5.68 (1H, dd, J ) 9, 15 Hz), 6.23
(1H, s), 6.45 (1H, dd, J ) 12, 15 Hz), 6.60 (1H, d, J ) 1.5 Hz),
6.75 (1H, d, J ) 12 Hz), 6.77 (1H, d, J ) 1.5 Hz), 7.22-7.40 (5H,
m). HRMS cacld for C41H52ClN3O10S2Na (M +Na)+, 868.2680;
found, 868.2670.
1
2f. White solid (36% yield). H NMR (CDCl3) δ 0.80 (3H, s),
1.19-1.23(1H,m), 1.28-1.36 (9H, m), 1.42-1.46(1H, m), 1.53-
1.63 (2H, m), 1.64 (3H, s), 1.80-1.89 (1H, m), 1.90-2.09 (1H,
m), 2.18 (1H, dd, J ) 3 and 14 Hz), 2.32 (3H, s), 2.33-2.42 (1H,
m), 2.49-2.62 (2H, m), 2.88 (3H, s), 3.04 (1H, d, J ) 9 Hz), 3.11
(1H,d,J ) 11 Hz), 3.23 (3H,s), 3.35 (3H,s), 3.49 (1H, d, J ) 9
Hz), 3.63 (1H, d, J ) 12 Hz), 3.98 (3H, s), 4.27 (1H, t, J ) 10
Hz), 4.79 (1H, dd, J ) 3 and 12 Hz), 5.41 (1H, q, J ) 7 Hz), 5.66
(1H, dd J ) 9 and 15 Hz), 6.21 (1H, s), 6.42 (1H, dd, J ) 11 and
15 Hz), 6.65 (1H, d, J ) 1.5 Hz), 6.73 (1H, d, J ) 11 Hz), 6.81
(1H, d, J ) 1.5 Hz). HRMS calcd for C38H54ClN3O10S2Na (M +
Na)+, 834.2837; found, 834.2819.
D-DM1SPh (6c). 1H NMR (CDCl3) δ 0.89 (3H, s), 1.31 (3H, d,
J ) 6.4 Hz), 1.48-1.53 (m, 1H), 1.51 (3H, d), 1.72 (3H, s), 2.10
(1 H, d, J ) 6 Hz), 2.15 (1H, dd, J ) 3, 15 Hz), 2.69 (1H, dd,
J ) 12, 15 Hz), 2.81-2.89 (2H, m), 2.96 (3H, s), 3.02 (1H, d, J )
7 Hz), 3.20 (3H, s), 3.36 (3H, s), 3.47 (1H, d, J ) 9 Hz), 3.55 (1H,
d, J ) 13 Hz), 3.68 (3H, s), 4.04 (3H, s), 4.31 (1H, t, J ) 11 Hz),
4.93 (1H, dd, J ) 3, 12 Hz), 5.20 (1H, q, J ) 7 Hz), 5.90 (1H, dd,
J ) 9, 15 Hz), 6.25 (1H, s), 6.27 (1H, d, J ) 12 Hz), 6.45 (1H, dd,
J ) 12, 15 Hz), 6.83 (1H, d, J ) 1.5 Hz, 6.89 (1H, d, J ) 1.5 Hz),
7.27-7.49 (5H, m). HRMS cacld for C41H52ClN3O10S2Na (M
+Na)+, 868.2680; found, 868.2672.
1
6f. White solid (30% yield) H NMR δ 0.869 (3H, s), 1.200-
N2′-Deacetyl-N2′-[3-(methyldithio)-1-oxobutyl]maytansine (D-
M2′SMe, 2d). Maytansinol (4) was reacted with N-methyl-N-3-
(methyldithio)-1-oxobutyl]-L-alanine (5d) as described above. The
reaction mixture was purified by preparative TLC on silica gel,
eluting twice with 7% MeOH in CHCl3. Two new UV absorbing
bands (Rf ) 0.65, 0.75) were obtained. The products were isolated
by extraction with ethyl acetate. The higher Rf band was determined
to be the D-aminoacyl ester 6d (31%), whereas the lower Rf band
was the desired L-aminoacyl ester 2d (44%). Both isomers were
further purified by HPLC using a Waters Radialpak C-18 column,
eluting at a flow rate of 2 mL/min with a linear gradient of
acetonitrile/water (50-80% acetonitrile/10 min). Under these
conditions, the D-aminoacyl ester had a retention time of 7.4 min,
whereas the L-aminoacyl isomer had a retention time of 7.6 min.
The diastereomeric purity of 2d and 6d were determined by HPLC
analysis using a Kromasil cyano column (250 mm × 4.6 mm, 10
micron particle size) at a flow rate of 1.50 mL/min, eluting with
an isocratic mixture of ethyl acetate/hexane/2-propanol (24:66:10/
v/v). Under these conditions, 2d eluted with a retention time of
11.96 min, and its D-alanyl 6d isomer eluted with a retention time
of 17.30 min.
1.315 (2H, m), 1.283 (3H, d, J ) 6.8 Hz), 1.373 (3H, dd, J ) 5.6,
1.2 Hz), 1.498 (3H, d, J ) 7.6 Hz), 1.600 (1H, d, J ) 14.4 Hz),
1.691 (3H, s), 1.772 (1H, m), 1.929 (2H, m), 2.203 (1H, dd, J )
11.6, 3.2 Hz), 2.421 (3H, s), 2.518 (2H, m), 2.654 (1H, t), 2.814
(1H, dd, J ) 8, 1.6 Hz), 2.902 (1H, m), 3.038 (3H, d, J ) 3.2 Hz),
3.164 (3H, s), 3.200 (1H, d, J ) 13.2 Hz), 3.339 (3H, s), 3.436
(1H, d, J ) 8 Hz), 3.507 (1H, d, J ) 12.8 Hz), 3.996 (3H, s),
4.309 (1H, t), 4.936 (1H, dd, J ) 4.8, 4 Hz), 5.093 (1H, m), 5.851
(1H, m), 6.233 (1H, d, J ) 11.2 Hz), 6.269 (1H, s), 6.429 (1H, dd,
J ) 10.8, 4.4 Hz), 6.792 (1H, s) and 6.848 (1H, s). HRMS calcd
for C38H54ClN3O10S2Na (M + Na)+, 834.2837; found, 834.2830.
N2′-Deacetyl-N2′-[4-(S)-(methyldithio)-1-oxopentyl]maytan-
sine (2g). Maytansinol (4) was coupled with N-methyl-N-[(4-(S)-
methyldithio)-1-oxopentyl]-S-alanine (5g) using DCC and zinc
chloride in dichloromethane as described above for the synthesis
of 2f. A mixture of 2 diastereomers bearing the N-methyl-L-alanyl
moiety (2g, S,S) and the N-methyl-D-alanyl moiety (6g, R,S) were
obtained. The diastereomers were separated by HPLC on a Kromasil
cyano column (4.6 mm × 250 mm), using an isocratic elution at a
flow arte of 1 mL/min with hexane/ethyl acetate/2-propanol (68:
24:8, v/v/v). Under these conditions, the isomer 2g (S,S) eluted at
24.5 min. The peak for the other isomer 6g (R,S) was well separated
and eluted at 34.6 min.
1
2d. H NMR (CDCl3) δ 0.803 (3H, s), 1.265 (2H, m), 1.280
(3H, d, J ) 2.4 Hz), 1.309 (3H, d, J ) 2.4 Hz), 1.638 (1H, d, J )
13.6 Hz), 1.643 (3H, s), 1.760 (1H, m), 2.051 (2H, m), 2.179 (1H,
dd, J ) 11.2, 2.8 Hz), 2.318 (3H, s), 2.365-2.536 (2H, m), 2.611
(1H, dd, J ) 12.4, 2 Hz), 2.719 (2H, m), 2.852 (3H, s), 3.033 (1H,
d, J ) 9.6 Hz), 3.110 (1H, d, J ) 12.4 Hz), 3.219 (3H, s), 3.355
(3H, s), 3.498 (1H, d, J ) 10.8 Hz), 3.657 (1H, d, J ) 12.4 Hz),
3.983 (3H, s), 4.284 (1H, t), 4.872 (1H, dd, J ) 8.8, 2.8 Hz), 5.660
(1H, dd, J ) 8.8, 5.6 Hz), 6.197 (1H, s), 6.430 (1H, dd, J ) 11.2,
4 Hz), 6.648 (1H, d, J ) 2 Hz), 6.740 (1H, d, J ) 11.6 Hz) and
1
2g. H NMR (CDCl3) δ 0.798 (3H, s), 1.197-1.267 (2H, m),
1.292 (3H, d, J ) 7.2 Hz), 1.283 (3H, d, J ) 2 Hz), 1.300 (3H, d,
J ) 1.2 Hz), 1.462 (1H, m), 1.536 (1H, d, J ) 8 Hz), 1.640 (3H,
s), 1.834-2.020 (2H, m), 2.176 (1H, dd, J ) 11.6, 2.8 Hz), 2.326
(3H, s), 2.373-2.522 (2H, m), 2.603 (1H, dd, J ) 12.4, 2 Hz),
2.847 (3H, s), 2.871-2.903 (1H, m), 3.028 (1H, d, J ) 9.6 Hz),
3.108 (1H, d, J ) 12.4 Hz), 3.223 (3H, s), 3.351 (3H, s), 3.499
(1H, d, J ) 9.2 Hz), 3.639 (1H, d, J ) 12.8 Hz), 3.983 (3H, s),