L. F. Tietze et al.
Conclusion
52.07 (C-2ꢅ), 63.05 (C-10ꢅ), 75.35, 75.53, 75.55 (CHCO
2
tBu), 82.64 (C-
A
H
U
G
E
N
N
3
)
3
2
2
1
1
’’), 118.54, 118.63, 121.95, 122.01 (C-5a’, C-9b’), 122.35, 122.38 (C-6’),
23.21 (C-9’), 123.60, 123.62 (C-7’), 127.00, 127.11, 127.22 (C-8’, C-1’’),
30.03 (C-9a’), 141.07, 141.11, 141.89, 141.91 (C-6’’, C-3a’), 147.99, 148.03
In conclusion, with prodrug (S,S)-7a we have successfully
developed a photoactivatable prodrug whose cytotoxicity
6
could be dramatically reduced by a factor of 2ꢄ10 in com-
(C-4’’), 151.97 (C-3’’), 152.44, 152.47 (C-5’), 166.45, 166.48 (C=O),
1
1
70.92 ppm (CON); HRMS (ESI): m/z: calcd for
C
57
H
56
N
4
O
18
:
parison to the parent seco-drug (ꢀ)-(S,S)-5 (IC =110 fm).
5
0
+
107.3482; found: 1107.3481 [M+Na] .
Compound (ꢀ)-(S,S)-5 can be formed from (S,S)-7a by ex-
Compound (S,S)-7a: A solution of alcohol (S,S)-15 (300 mg, 277 mmol,
.00 equiv) in CH Cl (30 mL) was cooled to 08C and treated with trie-
posure to UV-A light under relatively mild conditions with
1
2
2
ꢀ
2
an irradiation-power of only 2 Jcm . With a QIC of up to
5
0
thylamine (5.75 mL, 41.5 mmol, 150 equiv) and methanesulfonyl chloride
8200 it is well suited for a potential use in a selective cancer
(430 mL, 5.53 mmol, 20.0 equiv) and stirred for 45 min at room tempera-
therapy. In contrast, the introduction of an ortho-nitrobenzyl
moiety carrying a carboxylic acid group enhances the overall
cytotoxicity. Such an effect has not been described previous-
ture. The solution was poured into sat. NaHCO
with CH Cl (3ꢄ75 mL). The combined organic layers were dried over
MgSO and the solvent was removed under reduced pressure. The resi-
due was dried under high vacuum together with LiCl (410 mg,
.68 mmol, 20.0 equiv) for 1 h. Abs. DMF (30 mL) was added and the sol-
3
(75 mL) and extracted
2
2
4
[11]
ly for this class of protecting groups.
9
ution was stirred for 5.5 h at 758C. The reaction was monitored by HPLC
analysis. After cooling to room temperature, the solution was poured
into brine (90 mL) and extracted with CH
ganic layers were dried over MgSO , the solvent was removed, and the
residue was taken up in CH Cl and filtered over a hydrophobic syringe
filter. Purification on preparative HPLC gave the product (254 mg,
226 mmol, 82%) as a colorless solid. HPLC (analytical) t =12.32 min
2 2
Cl (3ꢄ75 mL). Combined or-
Experimental Section
4
2
2
General: All reactions were performed in flame-dried flasks under an
argon atmosphere. Solvents were dried according to common laboratory
techniques and freshly distilled prior to use. All reagents purchased from
commercial sources were used directly without further purification. TLC
analysis was performed on precoated silica gel SIL G/UV254 plates from
Merck and Silica gel 60 (0.040–0.063 mm) from Merck was used for
column chromatography. Vanillin in methanolic sulphuric acid (0.5 g va-
R
(Kromasil 100 C-18 250ꢄ4.6 mm, 5 mm) on a gradient: A=MeOH, B=
water; 0–6 min: 70A/30B!100A/0B, 6–9.5 min: 100A/0B, 9.5–10 min:
ꢀ
1
100A/0B!70A/30B, 10–15 min: 70A/30B, flow=0.8 mLmin
; HPLC
R
(preparative) t =26.18 min (Kromasil 100 C-18 250ꢄ4.6 mm, 5 mm) on a
gradient: A=MeOH, B=water; 0–25 min: 70A/30B!100A/0B, 25–
2 4
nillin, 3 mL conc. H SO , 85 mL methanol and 10 mL acetic acid) was
30 min: 100A/0B, 30–31 min: 100A/0B!70A/30B, 31–40 min: 70A/30B,
ꢀ
1
used as the staining agent for TLC analysis. Preparative separations were
performed on a HPLC system from Jasco equipped with two PU-2087
PLUS solvent pumps and a UV-2075 PLUS detector. As the stationary
phase a Kromasil 100 C18 (250ꢄ20 mm, particle size 7 mm) column in
combination with a Kromasil 100 C18 (50ꢄ20 mm, 5 mm) guard column
3
flow=18 mLmin ; UV (CH CN): lmax (lg e)=196 (4.920), 255 (4.828),
263 (4.820), 305 (4.260), 317 nm (4.326); IR (ATR): n˜ =2954, 2920, 2851,
1736, 1661, 1628, 1579, 1525, 1505, 1483, 1465, 1395, 1368, 1332, 1310,
ꢀ
1
1258, 1147, 1133, 1097, 1081, 1032, 965, 929, 844, 818, 755, 718 cm
;
1
H NMR (600 MHz, [D
possible): d=1.37 (s, 18H; C
(m , 4H; 2-H , 4-H ), 3.79–3.92 (m, 1H; 10’-H
), 4.14–4.27 (m, 2H; 1’-H, 2’-H ), 4.30–4.40 (m, 1H; 2’-H
9.2 Hz, 2H; OCH O), 6.45, 6.46 (2s, 1H; OCHCO tBu), 7.31, 7.35 (2s,
6
]DMSO; signals of diastereomers are assigned if
(CH ), 1.88–1.98 (m, 2H; 3-H ), 2.50–2.73
), 3.96–4.04 (m, 1H; 10’-
), 6.28 (t, J=
(
both from Jasco) was used. UV spectra were recorded by using a
A
H
U
G
R
N
U
G
3
)
3
2
Lambda 2 spectrometer from Perkin–Elmer or a V-630 spectrometer
from Jasco. IR spectra were recorded on a Bruker Vector 22 spectrome-
ter (KBr discs). An FTIR-4100 instrument from Jasco was used as well.
c
2
2
a
H
b
a
b
2
2
1
13
H and C NMR spectra were recorded on a Mercury 300, Unity 300 or
1H; 2’’-H), 7.43–7.47 (m, 1H; 7’-H), 7.56–7.60 (m, 1H; 8’-H), 7.76, 7.77
(2s, 1H; 5’’-H), 7.88 (d, J=8.3 Hz, 1H; 9’-H), 8.12, 8.14 (2s, 1H, 4’-H),
Inova 600 from Varian. Chemical shifts are reported in d (ppm). Residu-
al peaks of the deuterated solvents indicated were used as internal stand-
ards. For HPLC-MS the ESI mass spectrometry with the ion-trap mass
spectrometer LCQ (Finnigan) was used. The HPLC system comprises of
solvent pump Rheos 400, degasser ERC-3415a (Flux Instruments), auto-
sampler 851 (Jasco), and a diode array detector (Thermo). The column
was a Synergi Max-RP C12 (150 2 mm, 4 mm, phenomenex).
1
3
8.20 ppm (d, J=8.4 Hz, 1H; 6’-H); C NMR (125 MHz, [D
nals of diastereomers are assigned if possible): d=19.07 (C-3), 27.32 (C-
(CH ), 34.36 (C-2, C-4), 40.60, 40.71 (C-1’), 47.53, 47.62 (C-10’), 52.63
(C-2’), 75.32, 75.48 (OCHCO tBu), 82.71 (C(CH ), 99.15, 99.32 (C-4’),
103.80 (OCH O), 105.68, 105.70 (C-5’’), 106.88, 106.92 (C-2’’), 116.83,
116.92 (C-5a’), 122.00, 122.08 (C-6’), 122.53, 122.59 (C-9b’), 122.76 (C-9’),
23.85 (C-7’), 126.85, 126.99 (C-1’’), 127.72 (C-8’), 129.74 (C-9a’), 141.64
C-3a’), 141.93, 141.95 (C-6’’), 148.04, 148.07 (C-4’’), 151.98 (C-3’’),
53.06, 153.14 (C-5’), 166.40, 166.43 (CO tBu), 170.87, 170.90 ppm
CON); HRMS (ESI): m/z calcd for C57 16: 1143.2804; found:
6
]DMSO; sig-
A
H
U
G
R
N
U
G
3 3
)
2
A
H
U
G
E
N
N
3 3
)
2
1
(
Compound (S,S)-15:
18 mmol, 1.00 equiv), K
A
solution of diphenol (ꢀ)-(S,S)-14 (220 mg,
4
2
CO (173 mg, 1.25 mmol, 3.00 equiv), and pro-
3
1
2
tective group 11 (331 mg, 919 mmol, 2.20 equiv) in abs. DMF (30 mL) was
stirred for 16 h at room temperature. The solution was poured into brine
(
1
2 4
H54Cl N O
+
143.2811 [M+Na] .
(
100 mL) and extracted with CH
layers were washed with brine (3ꢄ150 mL), dried over MgSO
solvent was removed under reduced pressure. The product (335 mg,
08 mmol, 74%) was obtained by column chromatography on silica
CH Cl yellowish solid. =0.38 (CH Cl
/MeOH 75:1!25:1) as
MeOH 25:1); UV (CH CN): lmax (lg e)=194 (4.859), 256 (4.996), 264
4.983), 318 nm (4.514); IR (ATR): n˜ =1738, 1653, 1626, 1579, 1525, 1505,
2
Cl
2
(4ꢄ150 mL). The combined organic
4
, and the
Compound (S,S)-7b: Ester (S,S)-7a (36.3 mg, 32.6 mmol) was dissolved in
TFA (2.5 mL) and stirred for 30 min at room temperature. The solvent
was removed under reduced pressure and the residue was dried under
high vacuum. The product (39.9 mg, 29.5 mmol, 90%) was obtained as a
light-yellow solid. HPLC (analytical) t =16.56, 17.00, 17.36 min (Kroma-
R
sil 100 C-18 250ꢄ4.6 mm, 5 mm) on a gradient: A=MeOH, B=water+
3
(
2
2
a
R
f
2
2
/
3
(
ꢀ1
1
466, 1394, 1369, 1333, 1259, 1148, 1133, 1095, 1030, 928, 844, 757 cm
;
0.03% HCl; 0–15 min: 50A/50B!100A/0B, 15–25 min: 100A/0B, 25–
1
ꢀ1
H NMR (600 MHz, [D
6
]DMSO; signals of diastereomers are assigned if
(CH ), 1.88–1.97 (m, 2H; 3-H ),
), 3.37–3.45 (m, 1H; 10’-H ), 3.71–3.88 (m,
1’-H), 4.22 (m, 2H; 2’-H 2’-H ), 4.88–4.97 (m, 2H;
OH), 6.23–6.31 (m, 2H; OCH O), 6.42 (s, 1H; OCHCO tBu), 7.30,
.33 (2s, 1H; 2’’-H), 7.39–7.45 (m, 1H; 7’-H), 7.55 (t, J=7.6 Hz, 1H; 7’-
H), 7.76 (s, 1H; 5’’-H), 7.84 (d, J=8.3 Hz, 1H; 9’-H), 8.10, 8.12 (2s, 1H;
27 min: 100A/0B!50A/50B, 27–35 min: 50A/50B, flow=0.8 mLmin
;
possible): d=1.37, 1.38 (2s, 18H; C
A
H
U
G
R
N
N
3
)
3
2
UV (CH
3
CN): lmax (lg e)=195 (4.879), 255 (5.004), 263 (4.986), 306
2
2
CH
.51–2.71 (m
H; 10’-H
c
, 4H; 2-H
2
, 4-H
2
a
(4.431), 317 nm (4.500); IR (ATR): n˜ =1724, 1652, 1627, 1579, 1523, 1505,
ꢀ
1
1
b
,
a
,
b
1467, 1396, 1332, 1259, 1131, 1023, 982, 927, 756 cm
(600 MHz, [D ]DMSO; signals of diastereomers are assigned if possible):
d=1.87–1.96 (dd, J=14.3, 7.1 Hz, 2H; 3-H ), 2.51–2.71 (m , 4H; 2-H , 4-
), 3.80–3.91 (m, 1H; 10’-H ), 4.01 (dd, J=14.2, 6.4 Hz, 1H; 10’-H ),
4.15–4.26 (m, 2H; 1’-H, 2’-H ), 4.30–4.40 (m, 1H; 2’-H ), 6.20–6.30 (m,
2H; OCH O), 6.55, 6.56 (2s, 1H; OCHCO H), 7.29, 7.33 (2s, 1H; 2’’-H),
7.44 (t, J=7.6 Hz, 1H; 7’-H), 7.58 (t, J=7.6 Hz, 1H; 8’-H), 7.74, 7.75 (2s,
;
H NMR
2
2
2
6
7
2
c
2
H
2
a
b
1
3
4
’-H), 8.17 ppm (d, J=8.4 Hz, 1H; 6’-H);
]DMSO; signals of diastereomers are assigned if possible): d=19.08
C-3), 27.29, 27.30 (C(CH ), 34.32, 34.40 (C-2, C-4), 41.71, 41.74 (C-1’),
C NMR (125 MHz,
a
b
[
D
6
2
2
(
A
C
H
T
U
N
G
T
R
E
N
N
U
N
G
3 3
)
1730
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2013, 19, 1726 – 1731