Controlling the rates of reductively-activated elimination from the (indol-3-yl)methyl position of indolequinones

Article abstract of DOI:10.1039/b009652k

A series of substituted 3-(4-nitrophenyloxy)methylindole-4,7-diones (Q) were synthesised. The effects of substitution patterns on the indole core on rates of elimination of 4-nitrophenol as a model for drug release following fragmentation of a phenolic et

Full text of DOI:10.1039/b009652k

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Controlling the rates of reductively-activated elimination from the
(indol-3-yl)methyl position of indolequinones
Steven A. Everett,*a Matthew A. Naylor,a Paola Barraja,b Elizabeth Swann,b Kantilal B. Patel,a
Michael R. L. Stratford,a Anna R. Hudnott,b Borivoj Vojnovic,a Rosalind J. Locke,a
Peter Wardmana and Christopher J. Moodyb
2
a Gray Laboratory Cancer Research Trust, Mount Vernon Hospital, PO Box 100, Northwood,
Middlesex, UK HA6 2JR
b School of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 4QD
Received (in Cambridge, UK) 1st December 2000, Accepted 14th March 2001
First published as an Advance Article on the web 19th April 2001
A series of substituted 3-(4-nitrophenyloxy)methylindole-4,7-diones (Q) were synthesised. The effects of
substitution patterns on the indole core on rates of elimination of 4-nitrophenol as a model for drug release
Ϫ
ؒ
following fragmentation of a phenolic ether linker were studied. After reduction to either the radical anion (Q )
or hydroquinone (QH2) elimination of 4-nitrophenol occurred from the (indol-3-yl)methyl position. The half-lives
Ϫ
Ϫ3
ؒ
1
2
of Q radicals at [O ] ≈ 5 µmol dm , typical of tumour hypoxia, were t ≈ 0.3–1.8 ms, the higher values associated
–
2
with higher reduction potentials. Half-lives for the autoxidation of the QH2 were markedly longer at the same
oxygen concentration (t ≈ 8–102 min) and longer still in the presence of 4 µmol dmϪ3 superoxide dismutase
1
–
2
Ϫ
ؒ
1
(t ≈ 8–19 h). Although the indolequinones were able to eliminate 4-nitrophenol with high efficiency only Q
–
2
1
radicals of the 3-carbinyl substituted derivatives did so with sufficiently short half-lives (t ≈ 41–2 ms) to compete
–
2
with electron transfer to oxygen and therefore have the potential to target the leaving group to hypoxic tissue. The
1
hydroquinones are not sufficiently oxygen sensitive to prevent the elimination of 4-nitrophenol (t ≈ 1.5–3.5 s) even at
–
2
oxygen concentrations expected in normal tissue. By incorporating electron rich substituents at the indolyl carbinyl
position it is possible to control the rate of reductive fragmentation. This may prove an important factor in the design
of an indolequinone-based bioreductive drug delivery system.
Introduction
We have recently reported on the potential of indolequinones to
act as a reductively-activated drug delivery system.1–3 This class
of compound was shown to be able to efficiently eliminate a
variety of leaving groups from the (indol-3-yl)methyl position
upon reduction.2 Subsequent studies on the oxygen sensitive
reduction chemistry of this class of compound revealed that
the rate of reductive fragmentation is probably an important
determinant of prodrug selectivity for hypoxic tissues.4
Indolequinones have been considered of particular import-
ance in this field, because of the potential of indol-3-ylcarbinyl
substituents in such compounds to undergo an elimination
process upon reductive activation. This elimination chemistry,
through the intervention of ‘normal’ indole reactivity, is
suppressed in the quinone through delocalization into the
quinonoid vinylogous amide system. The archetypal indole-
quinone-based bioreductive drug is mitomycin C (1, Fig. 1),
Fig. 1 Structures of bioreductive quinones: compound 1 = mitomycin
which has been widely studied in this context, eliminating a
carbamate group from the equivalent position.5–7 Such pro-
cesses have been demonstrated previously with simpler benzo-
quinones8 and naphthoquinones9 bearing halide leaving groups
(e.g. 2 and 3, Fig. 1), but not with biologically useful leaving
groups. As depicted in Scheme 1 there are two possible reductive
pathways for fragmentation involving either one-electron
C; 2 = 2-CH2X-1,4-benzoquinone (X = leaving group); 3 = 2-CH2X-1,4-
napthoquinone (X = leaving group); 4 = substituted indolequinone.
a balance between the one-electron reduction potential (which
Ϫ
ؒ
governs the rate of Q radical scavenging by oxygen) and the
rate of reductive elimination from the (indol-3-yl)methyl pos-
Ϫ
ؒ
ition. If the reactivity of the Q radical with oxygen is much
faster than the rate of reductive elimination then the half-life of
Ϫ
ؒ
reduction to the intermediate semiquinone radical (Q )
catalysed in biological systems by for example, NADPH: cyto-
chrome c (P450) reductase10 and/or two-electron reduction to
the hydroquinone (QH2). The latter occurs biologically follow-
ing reduction by DT-diaphorase (NQO1),11–16 where QH2 is
Ϫ
ؒ
the Q radical may be too short to allow efficient release of a
leaving group even under severe hypoxia. Conversely, should
the rate of reductive elimination be much greater than the
Ϫ
ؒ
rate of Q radical reactivity with oxygen then the release of
the leaving group may also occur in normoxic tissue. Both
scenarios would limit the hypoxia-selectivity of these indole-
quinones which would rely entirely on two-electron reducing
Ϫ
ؒ
formed directly via hydride transfer, by-passing Q radical
formation.17 From a chemical kinetic point of view the selectiv-
ity of indolequinones for hypoxic tissue will require establishing
DOI: 10.1039/b009652k
J. Chem. Soc., Perkin Trans. 2, 2001, 843–860
This journal is © The Royal Society of Chemistry 2001
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Scheme 1 One- and two-electron reduction pathways leading to the
elimination of
indolequinones.
a leaving group (X) from 3-carbinyl-substituted
enzymes such as NQO1 to promote reductive elimination
directly from the hydroquinone.4,18
A series of indolequinones (4, Fig. 1) with varying alkyl and
aryl substituents were prepared. The derivatives studied
included those substituted on the exocyclic (indol-3-yl)carbinyl
group and bearing as a leaving group (X), the chromophoric
4-nitrophenol moiety (a model for drugs eliminated through
a phenolic ether linkage). The indolequinones were reduced
in a controlled and quantifiable manner using radiolytically-
produced reducing radicals. The rates of reductive elimination
Ϫ
ؒ
of the model leaving group from both Q radical and QH2
were determined by pulse radiolysis. These rates were then
Scheme 2 Reagents and conditions: (i) KOH, MeI, DMSO; (ii) HNO3,
AcOH; (iii) Sn, HCl; (iv) LiAlH4, THF; (v) Fremy’s salt, Me2CO,
NaH2PO4 buffer.
compared with the corresponding reactivities of the Q Ϫ radical
ؒ
and QH2 with oxygen with a view to controlling drug delivery
over the range of oxygen concentrations present in hypoxic
tumours.
Results
Synthesis
A number of indolequinones had been prepared previously.
New derivatives were prepared from 5-hydroxyindole-3-carb-
oxylates 5 obtained from the Nenitzescu reaction of 1,4-
benzoquinones with aminoalkenoates. Subsequent methylation
to 5-methoxyindole-3-carboxylates 6 and nitration gave 4-nitro-
indoles 7 in good yield, after chromatographic separation of
the minor 6-nitro isomer in some cases. Reduction of the nitro
group to the amine 8 was followed by further reduction of the
ester, and oxidation to the indolequinones using Fremy’s salt
(Scheme 2) except for 9 where the sequence of the ultimate step
was reversed. The starting materials for the indolequinones
28, 30 and 31 were the 3-acylindoles 10 prepared via their
N-bromomagnesyl (Grignard) indole derivatives. Treatment
with the appropriate acyl chloride then furnished the required
3-acylindoles 10, which were then converted into the indole-
quinones 28, 30 and 31 by way of the nitro compounds 11 and
acylquinones 12 (Scheme 3) using established methods.2,4 In
general, the 3-(hydroxymethyl)indolequinones 13–31 (Table 1)
were converted into the corresponding 3-(4-nitrophenoxy)
derivatives 32–50 by coupling to 4-nitrophenol under standard
conditions (Scheme 4).
Scheme 3 Reagents and conditions: (i) EtMgBr, Et2O then R3ЈCOCl;
(ii) NaH, MeI, THF; (iii) HNO3, AcOH; (iv) Sn, HCl; (v) Fremy’s salt;
(vi) NaBH4 then air.
Chemical kinetics
Table 2 contains the one-electron reduction potentials and rate
constants for the reaction of semiquinone radicals with oxygen,
and rates of hydroquinone autoxidation for the corresponding
alcohols 13–31. Table 3 contains the rate constants for the
reductive elimination of 4-nitrophenol plus the leaving group
efficiencies of the 3-carbinyl substituted indolequinones under
study 32–50. The indolequinone alcohols 13–31 exhibit much
poorer leaving group ability [leaving group (H2O) pKa = 15.7]
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Table 1 3-Hydroxymethylindole-4,7-diones 13–31 and their corresponding 3-(4-nitrophenoxy)alkyl indolequinones 32–50
CH2OH indole
R1
R2
R3Ј
R5
R6
CH2OAr indole
13a
14b
15b
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Me
-(CH2)3-
Me
Me
Me
Me
Me
Me
H
—
Me
Me
Me
Ph
4-Ph-C6H4
2-Naphthyl
Me
Et
Me
Me
Me
Me
Me
Me
Me
H
H
H
H
H
H
H
H
H
H
H
H
H
H
H
Me
MeO
MeO
MeO
MeO
Morpholino
MeO
MeO
MeO
MeO
MeO
MeO
MeO
MeO
MeO
MeO
MeO
H
H
H
Me
H
H
H
H
H
H
H
Me
H
H
Me
H
H
H
H
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
c-Pr
CH2Ph
Ph
Ph
4-F-C6H4
n-Pr
n-Pr
Me
Me
Me
Me
Ph
2-Thienyl
4-Methylpiperazin-1-yl
MeO
MeO
Me
Me
Me
a Ref. 2. b Ref. 13.
Scheme 4 Reagents and conditions: (i) SOCl2–CH2Cl2 then 4-NO2-
C6H4-OH–NaH–DMF; (ii) 4-NO2-C6H4-OH–Ph3P–DEAD–THF.
than their corresponding 4-nitrophenol conjugates [leaving
group (4-nitrophenol) pKa = 7.8 0.1] but their redox proper-
ties do not differ appreciably. The oxygen sensitivity of the
semiquinone radical and hydroquinone autoxidation of 13–31
will parallel that of their 4-nitrophenoxy derivatives 32–50, but
measurements could be made without interference from the
reductive elimination of the leaving group.
Fig. 2 Absorption spectra obtained on the reduction of 34 (40 µmol
dmϪ3) by the (CH3)2C OH radical at pH 9.3: (–᭹–) 200 µs, (–ᮀ–) 100
ؒ
ms and (–᭺–) 10 s after the pulse. All absorbances were normalized to a
Ϫ3
ؒ
dose of 16 Gy corresponding to [(CH3)2C OH] ≈ 11 µmol dm in a 2
cm path length optical cell.
(RNO2 Ϫ), indicating that the reduction of 34 generates pre-
ؒ
Ϫ
ؒ
Rates of reductive elimination of 4-nitrophenol from substi-
tuted indolequinones. Elimination of 4-nitrophenol could feas-
ibly occur either from the one-electron reduction of the parent
dominantly (∼96%) Q radical. The rate constant for the
ؒ
reduction of 4-nitrophenol by (CH3)2C OH was determined
Ϫ
ؒ
from the first-order build-up of the RNO2 anion radical at
300 nm at [4-nitrophenol] ≈ 25–200 µmol dmϪ3 in propan-2-ol–
water (50%, v/v) at pH 7.4 and was slower than that previously
determined in propanol–water (95/5%, v/v) by conductivity
detection.19 From the pH dependence of the absorption at 345
indolequinones to the semiquinone radical (Q Ϫ) or two-
ؒ
electron reduction to the hydroquinone (QH2) as depicted in
Scheme 1. Indolequinones were rapidly reduced by the propan-
9
3
Ϫ1
ؒ
2-ol (CH3)2C OH radical (k1 ≈ 10 dm mol
Q
s
Ϫ1) to generate
Ϫ radicals via reaction (1).
nm, a pKa (QH /Q Ϫ) = 5.2 0.1 for 15 was obtained indicating
that the semiquinone radical is deprotonated at physiological
pH, which is expected to be the case for all 4-nitrophenol
conjugates 32–50.
ؒ
ؒ
ؒ
Q + (CH3)2C OH → Q Ϫ + (CH3)2CO + H+
(1)
ؒ
ؒ
At pH 4.5 the semiquinone radical absorption of 34 recorded
at 345 nm decayed via pure second order kinetics with a half-life
which decreased with increasing radiation dose or initial con-
Fig. 2 shows the absorption spectra obtained by pulse radio-
lysis of an N2O-saturated propan-2-ol–water mixture (50%,
v/v) containing 40 µmol dmϪ3 34, in potassium phosphate
buffer (4 mmol dmϪ3) at pH 7.4. The initial spectrum observed
ؒ
centration of reducing radicals ([(CH3)2C OH] ≈ 3–30 µmol
dmϪ3), indicating that the semiquinone radical decays pre-
dominantly by a radical–radical reaction to generate the hydro-
quinone via reaction (2).
∼200 µs after the electron pulse is characteristic of the Q Ϫ rad-
ؒ
ical generated in reaction (1) and was virtually identical to that
obtained on reduction of the alcohol 15. Similar spectra were
previously observed on the reduction of (5-methoxy-1-methyl-
4,7-dioxoindol-3-yl)methyl derivatives.2 The rate constant for
Ϫ
ؒ
ؒ
Q
+ Q Ϫ + 2H+
QH2 + Q
(2)
ؒ
the reduction of the alcohol 15 by the (CH3)2C OH radical was
determined to be k1 = (4.1 0.1) × 109 dm3 molϪ1 sϪ1, over one
order of magnitude faster than the reduction of 4-nitrophenol
k = (1.5 0.1) × 108 dm3 molϪ1 sϪ1 to the nitro anion radical
The reciprocal of the first half-life of the semiquinone radical
varied linearly with the initial radical concentration, and from
the slope of the fitted straight line, the rate constant 2k2 =
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(8.2 0.1) × 107 dm3 molϪ1 sϪ1 was obtained at pH 4.5. At pH
Ϫ
ؒ
7.4 (where the Q radical is fully deprotonated), the rate of
second-order decay decreases by an order of magnitude to
2k2 = (1.1 0.1) × 107 dm3 molϪ1 sϪ1 and the plot of the
reciprocal of the first half-life of the semiquinone radical versus
the initial radical concentration did not pass through the origin
but gave an intercept indicative of a competing first-order
process. The decay kinetics of the Q Ϫ radical were independent
ؒ
of the concentration of 34 ≈ 30–100 µmol dmϪ3 confirming a
unimolecular first-order decay pathway which was ascribed to
intramolecular fragmentation of the indolequinone conjugate
and elimination of the leaving group (LG = 4-nitrophenol) as
shown in reaction (3). This gave an estimate of k3 ≈ 20–50 sϪ1
which was more accurately determined from observing the
release of the 4-nitrophenol chromophore.
Ϫ
(Q–LG) → Q + + LG
(3)
ؒ
ؒ
In propan-2-ol–water (50%, v/v) 4-nitrophenol has
a
pKa = 7.8 0.1 and when deprotonated exhibits an absorption
maximum at ∼420 nm. At pH > 6 the decay of the Q Ϫ radical is
ؒ
Fig. 3 Transient absorption traces recorded at 410 nm on the pulse
radiolysis of either 35 or 48 (50 µmol dmϪ3) in an N2O-saturated
propan-2-ol–water mixture (50%, v/v) at pH 9.3 and 7.4 respectively.
Panels a and b show the biphasic reductive elimination of 4-nitrophenol
on two different timescales when a dose per pulse of 15.5 Gy equivalent
associated with an increase in absorption in the 350–500 nm
region ascribed to the reductive elimination of the 4-nitro-
phenoxide anion as shown in Fig. 2. At pH < 6, 4-nitrophenol
does not absorb above 400 nm and the only absorption
to [(CH3)2C OH] = 10. 4 µmol dmϪ3 was used. Panels c and d show the
ؒ
observed is that of the Q Ϫ radical. The reductive elimination of
ؒ
reductive elimination of 4-nitrophenol from the semiquinone radical of
Ϫ3
ؒ
48 on two different timescales when [(CH3)2C OH] = 5.4 µmol dm
.
4-nitrophenol from 34 is biphasic; the first phase complete by
Each of the kinetic traces is overlapped by a simulated trace which best
∼100 ms and a much slower second phase which is complete by
fits the experimental data.
Ϫ
Ϫ
ؒ
ؒ
10 s after reduction to the Q radical. The fact that the Q
radical of the alcohol 15 decayed by pure second-order kinetics
Ϫ3
over a broad pH range 3–9.5 (even at low [Q Ϫ] ≈ 1.5 µmol
JϪ1). When [(CH3)2C OH] > 16 µmol dm the semiquinone
ؒ
ؒ
dmϪ3) confirmed that the position of the equilibrium reaction
radical decays predominantly via reaction (2) and G(4-nitro-
(2) lay well to the side of the hydroquinone and that negligible
phenol) ≈ 0.3 µmol JϪ1 correlates well with the expected
Ϫ
ؒ
G(QH2) = 0.33 µmol JϪ1 i.e. one-half of G(Q Ϫ) = 0.67 µmol JϪ1
.
ؒ
quantities of the Q radicals would be generated by the back
reaction on the timescale of 4-nitrophenol release. At low initial
Ϫ3
ؒ
At low [(CH3)2C OH] ≈ 5 µmol dm
the elimination of
radical concentrations (when [Q Ϫ] ≈ 1.5 µmol dmϪ3), the first
4-nitrophenol directly from the Q radical begins to compete
with reaction (2) and as a consequence the radiation chemical
yield of 4-nitrophenol increases to G(4-nitrophenol) ≈ 0.54
µmol JϪ1 and the contribution of the QH2 to the overall yield of
4-nitrophenol decreases from 70 to 25%.
Ϫ
ؒ
ؒ
phase of 4-nitrophenol release could be fitted to first-order
kinetics and gave an estimate for k3 ≈ 40 sϪ1 falling in the range
of that determined from the decay of the Q Ϫ radical. Neverthe-
ؒ
less, even under optimal experimental conditions approximately
10% of Q Ϫ radicals would be expected to decay via reaction (2)
More accurate determinations of the rates of reductive
ؒ
and as a consequence the rate constant k3 ≈ 40 sϪ1 would be an
elimination of 4-nitrophenol from both the Q radical and
QH2 were made using a data fitting model in FACSIMILE. A
model comprising reactions (2)–(4) was used to give ‘best’ fits to
kinetic traces of 4-nitrophenol versus time traces obtained by
pulse radiolysis. Fig. 3a and 3b show typical fits to kinetic data
obtained 5 s and 1.1 s respectively, after the reduction of 35.
Rate constants for the reductive elimination of 4-nitrophenol
from both the semiquinone radical and hydroquinone for all the
3-carbinyl substituted indolequinones 32–50 at pH 7.4 are dis-
played in Table 3. Rates of elimination from the Q radical
varied by over 2 orders of magnitude from k3 ≈ 3–354 sϪ1 and
were always significantly faster than the corresponding rates of
elimination from the hydroquinone. It was not possible to
determine k4 for the indolequinones 47, 48 and 50 since even at
Ϫ
ؒ
over-estimation of the actual value. The half-life for the dispro-
Ϫ
ؒ
portionation of Q radicals via reaction (2) at pH 7.4 and 12
7
Ϫ6
Gy ≈ [Q Ϫ] ≈ 8 µmol dmϪ3 is t ≈ (1.1 × 10 × 8 × 10
)
Ϫ1 ≈ 11
ؒ
1
2
–
ms which can compete with the elimination of 4-nitrophenol
Ϫ
ؒ
1
2
directly from the Q radical t ≈ (0.7/40) ≈ 15 ms via reaction
–
(3). This second slower phase of 4-nitrophenol release was
ascribed to the reductive elimination of chromophore from the
hydroquinone QH2 in reaction (4).
Ϫ
ؒ
(QH2–LG) → QH2+ + LGϪ
(4)
The slower elimination of 4-nitrophenol occurred on a time-
scale of seconds and the observed rate of 4-nitrophenol release
was k4 ≈ 0.3 sϪ1, significantly slower than from the Q Ϫ radical.
high [(CH3)2C OH] ≈ 30 µmol dm the release of 4-nitro-
Ϫ3
ؒ
ؒ
Ϫ
ؒ
Further evidence for this designation was obtained by compar-
ing the effect of the initial radical concentrations on the
radiation chemical yields of 4-nitrophenol at different pHs.
Radiation chemical yields G(4-nitrophenol)/µmol JϪ1 were
determined from absorbance measurements at 420 nm and
some 10 s after the initial reduction of 34, by which time semi-
quinone radicals had completely decayed and the reductive
elimination of 4-nitrophenol was complete. The corresponding
extinction coefficients for 4-nitrophenol in propan-2-ol–water
phenol from the Q radical could easily out-compete the
formation of QH2 by reaction (2). Fig. 3c and 3d show fits to
kinetic data obtained from the reduction of 48 after 10 and
2.5 ms respectively. As expected the reduction of 48 to the
Ϫ
ؒ
Q
radical results in stoichiometric release of the leaving
group i.e. [Q Ϫ] ≈ [4-nitrophenol] = 5.4 µmol dmϪ3
.
ؒ
Efficiencies of 4-nitrophenol release. The leaving group chem-
istry of the indolequinones was investigated by product analysis
(HPLC) following γ-radiolysis of N2O-saturated solutions con-
taining quinones (100 µmol dmϪ3) and propan-2-ol (8.3 mol
dmϪ3, 50%, v/v) at pH 7.4. The radiation chemical yield of
(50%, v/v) at pH 9.3 and 7.4 were determined to be ε420
=
8.72 × 103 and 3.54 × 103 dm3 molϪ1 cmϪ1 respectively. At pH
9.3, as the initial radical concentration decreased ([(CH3)2-
C OH] ≈ 16–1.5 µmol dmϪ3) the radiation chemical yield of
the (CH3)2C OH radical in N2O-saturated propan-2-ol–water
ؒ
ؒ
4-nitrophenol increased (G(4-nitrophenol) ≈ 0.3–0.54 µmol
mixtures was determined by ferricyanide reduction to be
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Fig. 5 Autoxidation of the hydroquinone of 15 in oxygen-saturated
Fig. 4 HPLC chromatogram showing a typical product profile
obtained by the γ-radiolysis (8 Gy) of 38 (40 µmol dmϪ3) in an N2O-
saturated propan-2-ol–water mixture (50%, v/v) containing phosphate
buffer (4 mmol dmϪ3) at pH 7.4.
0.1 mol dmϪ3 propan-2-ol and 200 µmol dmϪ3 phosphate buffer at pH
7.4. Spectrum measured at 10 s intervals. Insert: restoration of the
ground-state absorption of 7 at 292 nm following the autoxidation of
the hydroquinone in the presence of 650 µmol dmϪ3 oxygen.
G((CH3)2C OH) = 0.67 0.02 µmol JϪ1 in propan-2-ol–water
This is consistent with the fact that for quinones in general
where reduction potentials are lower than Ϫ200 mV, manipu-
lation of the redox potential will prove unsuccessful in modify-
ing significantly the rate of reaction (6).20
ؒ
(50%, v/v) and 0.72 0.01 µmol JϪ1 in 1 mol dmϪ3 propan-2-ol.
Fig. 4 shows the product profile obtained on the reduction of
38 by the (CH3)2C OH radical and is characteristic of that
ؒ
obtained for all the 4-nitrophenol conjugates under study. Loss
of the parent quinone 38 (G(–Q) = 2.2 0.01 µmol JϪ1) paral-
leled the formation of the 4-nitrophenol leaving group (LG)
with G(4-nitrophenol) = 1.6 0.15 µmol JϪ1 (∼ 73% efficiency),
both more than double the input of reducing (single-electron)
equivalents. The two remaining major peaks in Fig. 4 were
derived from the reaction of the resultant iminium derivative
with water to generate the alcohol 19 and with the propan-2-ol
to generate the isopropyl ether 51 (also synthesised independ-
ently). Both of these quinones are generated by autoxidation of
their respective hydroquinones via reaction (5) following the
unavoidable introduction of oxygen during HPLC sampling.
Hydroxymethyl compounds 13–31 exhibit much poorer
leaving group behavior than 4-nitrophenol and were therefore
considered good candidates for the study of hydroquinone
autoxidation without the added complication of reductive elim-
ination of leaving groups. HPLC confirmed that under the
conditions employed for radiolytic reduction (0.1 mol dmϪ3
propan-2-ol and 0.2 mmol dmϪ3 phosphate buffer) the hydro-
quinones derived from the isopropyl ethers or monophosphates
(both indicative of H2O lost) would make a negligible contribu-
tion to the observed rates of autoxidation. Fig. 5 shows the
spectral changes which occur when 15 is reduced incrementally
(5 Gy) by increasing doses of between 0–55 Gy or 0–40 µmol
dmϪ3 (CH3)2C OH radicals. The insert in Fig. 5 shows a typical
ؒ
trace recorded at 292 nm showing the autoxidation of the
hydroquinone and regeneration of the parent indolequinone 15
absorption in the presence of oxygen [O2] ≈ 650 µmol dmϪ3. The
autoxidation of the hydroquinone of 15 was not pure first-
order in oxygen concentration, but in every case the half-life did
decrease significantly with increasing oxygen concentration.
Thus for the hydroquinone of 15, first-order rate constants of
k5 ≈ 170 and ≈ 280 sϪ1 were measured for [O2] = 110 and 650
µmol dmϪ3 respectively. In marked contrast to the very rapid
reactivity of the semiquinone radicals with oxygen in reaction
(6), the autoxidation of the corresponding hydroquinones
(QH2) via reaction (5) occurs many orders of magnitude slower,
with apparent values falling in the range k5 ≈ 40–300 dm3 molϪ1
sϪ1 (see Table 2). It is noted that rates of autoxidation for
hydroquinones corresponding to 13–31 are all slower than that
previously determined for both radiolytic4 and enzymatic
QH2 + O2 → Q + H2O2
(5)
As expected, the relative yields of 19 and isopropyl ether 51
were dependent on the alcohol concentration, with the alkyl-
ation product 51 virtually disappearing when radiolysis was
performed in 1 mol dmϪ3 propan-2-ol. As shown in Table 3 all
the indolequinones reductively eliminated 4-nitrophenol with
high efficiency (typically >70%) although both G(ϪQ)/µmol
JϪ1 and G(4-nitrophenol)/µmol JϪ1 were significantly greater
(G(ϪQ) = 1.1–2.2 µmol JϪ1) than expected from the bimolecular
Ϫ
ؒ
decay of Q radicals via reaction (2) where the expected
G(ϪQ) = 0.33 µmol JϪ1 (i.e. one-half of G((CH3)2C OH) = 0.67
ؒ
µmol JϪ1 determined by ferricyanide reduction). Reduction of
2,6-dimethylbenzoquinone to its hydroquinone under the same
experimental conditions gave the expected G(ϪQ) = 0.37 0.01
µmol JϪ1 and G(QH2) = 0.32 0.03 µmol JϪ1 and confirmed the
presence of a chain reaction in the reduction of the indole-
quinones which occurred beyond the timescale of 4-nitrophenol
release observed by pulse radiolysis. This chain reaction was
previously observed for the reduction of (5-methoxy-1-methyl-
4,7-dioxoindol-3-yl)methyl derivatives under similar experi-
mental conditions.2,4
reduction21 of the drug EO9 where k5 ≈ 2.4 × 103 dm3 molϪ1 sϪ1
.
Reaction (5) represents the overall stoichiometry of QH2
autoxidation but is an oversimplification of a more complex
Ϫ
ؒ
kinetic system involving the O2 radical as an intermediate
including reactions (2), (6)–(8).22,23
Ϫ
O2 + QH2 → Q Ϫ + H2O2
(7)
(8)
ؒ
ؒ
Semiquinone and hydroquinone reactivities with oxygen. The
one-electron reduction potentials for selected indolequinone
alcohols 13–31 are displayed in Table 2 and vary by ∼100 mV,
O2 + O2 Ϫ + 2H+ → H2O2 + O2
Ϫ
ؒ
ؒ
falling in the range E(Q/Q Ϫ) ≈ Ϫ376 to Ϫ277 mV. The corre-
ؒ
Our previous studies have shown that in the absence of oxy-
gen the equilibrium reaction (2) favours the formation of the
sponding rates of electron transfer from the Q Ϫ radical to oxy-
ؒ
gen in reaction (6) remain rather fast k6 ≈ 1.3–6.4 × 108 dm3
ؒ
4
Ϫ
hydroquinone. However, Q exists in equilibrium with both
molϪ1 sϪ1
.
ؒ
Ϫ
QH2 and Q and the rapid reactivity of Q with oxygen pro-
duces the O2 Ϫ radical via reaction (6). In the absence of super-
ؒ
Ϫ
ؒ
Ϫ
ؒ
Q
+ O2 → Q + O2
(6)
oxide dismutase (SOD) which catalyses the disproportionation
J. Chem. Soc., Perkin Trans. 2, 2001, 843–860
849

View Article Online
of O2 Ϫ radicals in cells via reaction (8), reaction (7) may repre-
would imply that the only strategy capable of controlling
release over a range of oxygen tensions would require modify-
ing the rate of release of the leaving group (4-nitrophenol in this
study). Many of the substitutions at the 1- and 2-positions of
the indolequinone ‘core’ reduced the rate of reductive elimin-
ation 10-fold (e.g. 37–39). However, the 3-carbinyl substituted
analogues 47, 48 and 50 exhibited faster rates of 4-nitrophenol
release than 34. Parallels can be drawn with the reduction
of nitrobenzyl halides where α-substitution with methyl
increased the rate of fragmentation and release of halide ion
by decreasing the bond dissociation energy of the linker
through stabilization of the resultant nitrobenzyl radical.26
Interestingly, although phenyl substitution in analogue 49
was expected to facilitate fragmentation by stabilizing the
resultant radical cation, the rate of 4-nitrophenol release was
slower than that of the unsubstituted indolequinone 34. This
may reflect distortion from planarity and impaired p-orbital
overlap.
ؒ
sent the rate determining step in QH2 autoxidation when Q is
reduced radiolytically. Under our experimental conditions
<50% of Q is reduced to QH2 prior to mixing with oxygen and
this would be expected to influence the position of the equi-
librium reaction (2) and therefore the measured rate of QH2
autoxidation. The mixing of SOD (∼4 µmol dmϪ3 after mixing,
a biologically representative concentration) with QH2 resulted
in a significant reduction in the apparent rate constant of 15
QH2 autoxidation, to k5 ≈ 2–83 dm3 molϪ1 sϪ1 (see Table 2). This
is consistent with the involvement of O2 Ϫradicals in the overall
ؒ
autoxidation.24
Discussion
In this work we have determined the rates of elimination and
release of a model leaving group from indolequinone semi-
quinone and hydroquinone intermediates and also their corre-
sponding rates of reaction with molecular oxygen. From a
chemical kinetic point of view the selectivity of indolequinones
for hypoxic environments will rely on establishing a balance
between the one-electron reduction potential (which governs
the rate of semiquinone radical reactivity with oxygen) and the
rate of reductive elimination from these 3-carbinyl substituted
derivatives. In most normal tissues, values of pO2 < 10 mmHg
or 1.3% O2 are rarely observed, but such levels are common to
many solid tumours.25 If the reactivity of the semiquinone
radical towards oxygen is faster than the rate of reductive
elimination, the half-life of the semiquinone radical at tumour
relevant oxygen tensions will be too short to allow efficient drug
release even under severe hypoxia. It is immediately obvious
that in hypoxic tumour cells where [O2] ≈ 5 µmol dmϪ3, the
semiquinone radical of 15 reacts with oxygen with a first-order
rate constant of k6 = 5.2 × 108 × 5 × 10Ϫ6 ≈ 2.6 × 103 sϪ1 (half-
Conclusion
The semiquinone radical derived from the R3Ј-methyl substi-
tuted analogue 47 exhibits the fastest rate of elimination of
1
4-nitrophenol (t ≈ 2 ms) and is therefore capable of competing
–
2
1
2
against electron transfer to oxygen (t ≈ 1.6 ms) at [O ] ≈ 5 µmol
–
2
dmϪ3 (a value typical of tumour hypoxia). However, 5 µmol
dmϪ3 O2 prevented elimination of 4-nitrophenol from 34.
Therefore 3-carbinyl substituted compounds with simple alkyl
(e.g. methyl, 47) or electron rich heterocyclic groups, (e.g.
2-thienyl, 50) eliminate the model drug at a rate that can com-
pete with oxygen at this concentration. It should be noted that
3-carbinyl substitution may not be the only structural feature
which determines the rate of fragmentation on reduction. The
use of 4-nitrophenol as a model leaving group in this study has
facilitated structural optimisation of the indolequinone moiety
but clearly the nature of the leaving group itself must also be
considered in the design of novel drugs which are capable of
selective fragmentation in hypoxic tissue.
1
life, t = 0.7/k [O ] ≈ 270 µs). Elimination of 4-nitrophenol from
–
6
2
2
the semiquinone radical of 34 is therefore too slow (half-life,
t = 0.7/k ≈ 28 ms) to compete effectively with reaction (6). As
1
2
–
3
expected the reductive elimination of 4-nitrophenol from 34
was completely inhibited by 5 µmol dmϪ3 O2 during pulse
radiolysis and steady-state γ-radiolysis. Conversely, the rate of
autoxidation of the hydroquinone of 15 at the same oxygen
concentration k5 ≈ 240 (average) × 5 × 10Ϫ6 ≈ 1.2 × 10Ϫ3 sϪ1
Experimental
General procedures
1
(t ≈ 580 s), indicating that reaction of the hydroquinone
–
2
derived from 34 with oxygen will be too slow to compete with
NMR spectra: J values are given in Hz. UV–VIS spectra:
ε values are given in dm3 molϪ1 cmϪ1. Elemental analyses were
determined at the University of Exeter or by MEDAC Ltd.
(Egham, Surrey, UK) and all compounds characterized by
HRMS were chromatographically homogeneous. Solutions
in organic solvents were dried by standard procedures,
and dimethylformamide, toluene and tetrahydrofuran were
anhydrous commercial grades. Silica gel for flash column
chromatography was Merck Kieselgel 60 H grade (230–400
mesh) or Matrex silica 60.
1
reductive elimination of 4-nitrophenol (t ≈ 2 s). Indeed, the
–
2
rate of autoxidation could be significantly slower in vivo if
Ϫ
ؒ
SOD rapidly removes O2 radicals via reaction (8), rate
k5 ≈ 5 × 5 × 10Ϫ6 ≈ 2.5 × 10Ϫ5 sϪ1 (t ≈ 8 h). Thus, although the
1
–
2
reduction of 3-carbinyl substituted indolequinones to their
hydroquinones, which may be effected in vivo via two-electron
reducing enzymes such as NQO1, results in efficient elimination
of the substituent, this reaction is not inhibited by even normal
tissue oxygen concentrations. Therefore based on kinetic argu-
ments, such compounds would not be expected to be hypoxia-
selective per se, and will only target such environments in vivo if
the corresponding enzymes are actually up-regulated, which is
the case for some solid tumours.15 However, there is now com-
pelling evidence that indolequinones substituted at the (indol-3-
yl)methyl position are exceptionally poor substrates for NQO1,
and in certain cases the resultant iminium derivative formed on
reductive elimination from the hydroquinone actually inhibits
the enzyme.12,13 For example, the indolequinone alcohol 18 is
efficiently metabolised by NQO1 while the corresponding
4-nitrophenoxy conjugate 37 is not.13 The exploitation of the
oxygen-sensitive reduction chemistry of these indolequinones
to the semiquinone radical is therefore most likely to be the only
way to attain hypoxia-selectivity in tumour cells.
Materials
4-Nitrophenol, 1,1Ј-dimethyl-4,4Ј-bipyridinium dichloride
(methyl viologen, MV2+), 1,1Ј-dibenzyl-4,4Ј-bipyridinium
dichloride (benzyl viologen, BV2+), propan-2-ol and superoxide
dismutase (SOD) were obtained from Sigma-Aldrich Chemical
Company Ltd (Gillingham, Dorset, UK). Nitrous oxide,
oxygen and mixtures thereof were obtained from the British
Oxygen Company (Gillingham, Kent, UK). The follow-
ing compounds were obtained from Maybridge Chemical
Company Ltd (Tintagel, Cornwall, UK): methyl 3-(methyl)-
aminobut-2-enoate, ethyl 3-(phenyl)aminobut-2-enoate, ethyl
3-(4-fluorophenyl)aminobut-2-enoate, ethyl 1-cyclopropyl-5-
hydroxy-2-methylindole-3-carboxylate 5c, methyl 1-benzyl-2-
ethyl-5-hydroxyindole-3-carboxylate 5d and ethyl 5-hydroxy-2-
methyl-1-phenylindole-3-carboxylate 5e.
The redox potentials of these compounds are not changed
sufficiently by chemical modification to significantly lengthen
the half-life of the semiquinone radicals under hypoxia. This
850
J. Chem. Soc., Perkin Trans. 2, 2001, 843–860

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Pulse radiolysis
saturated propan-2-ol–water (50%, v/v) as determined by ferri-
cyanide reduction. Dose rates of 5.9 to 6.5 Gy minϪ1 were used,
as determined by Fricke dosimetry.32 For studies on the aut-
oxidation of the reduced forms of selected indolequinones,
steady-state γ-radiolysis of N2-saturated solutions of Q (50
µmol dmϪ3) in 0.1 mol dmϪ3 propan-2-ol and phosphate buffer
(NaH2PO4–Na2HPO4, 0.2 mmol dmϪ3, pH 7.4) was performed
in 20 cm3 hypodermic syringes (Popper & Sons, USA). In this
The redox properties of the indolequinones and the kinetic
characteristics of their semiquinone radicals (Q Ϫ) were investi-
ؒ
gated by pulse radiolysis. Semiquinone radicals were generated
following reduction of the parent indolequinone by the propan-
2-ol radical (CH3)2C OH. Kinetic spectrophotometry with sub-
ؒ
microsecond time resolution was used to monitor the reactions
Ϫ
ؒ
of Q radical and the reductive elimination of 4-nitrophenol.
Experiments were performed using a 6 MeV linear accelerator
as described previously.2 The absorbed radiation dose per
electron pulse (typically 1–30 Gy) was determined by the
thiocyanate dosimeter.27
case, an absorbed dose of 1 Gy = 0.72 µmol dmϪ3 (CH3)2C OH
ؒ
radicals and a dose rate of 5.9 Gy minϪ1 was employed.
High-performance liquid chromatography
The potentials were determined by establishing redox equi-
libria with a viologen (V2+) of known reduction potential.
Typically, solutions consisted of N2O-saturated propan-2-ol
(1–6.5 mol dmϪ3) and phosphate buffer (NaH2PO4–Na2HPO4,
4 mmol dmϪ3, pH 7.4–8.5) with Q (0–30 µmol dmϪ3) and V2+
(0–5 mmol dmϪ3). The alcohol converts the radiolytically-
Product analysis following γ-radiolysis of indolequinone solu-
tions was performed by gradient separation on a 100 mm × 3.2
mm base-deactivated reversed-phase column (Hichrom RPB,
Hichrom, Reading, UK) at a flow rate of 1 cm3 minϪ1. The
solvents and gradients used in the separation of products are
displayed in Table 4. Detection was at 228 nm using a Waters
486 detector (Watford, UK) and concentrations were deter-
mined from peak areas using Waters Maxima Software.
ؒ
ؒ
generated OH and H radicals in <2 µs to the propan-2-ol
ؒ
radical ((CH3)2C OH) which rapidly reduces both the indole-
quinones and V2+ to the Q Ϫ radical or viologen radical-cation
ؒ
+
ؒ
(V ). Absorbances were measured at 600 nm at a dose per
Stopped-flow experiments
pulse of 3 Gy (or ∼2 µmol dmϪ3 (CH3)2C OH radicals). Redox
ؒ
equilibration usually occurred within ∼100 µs (during which
time there was negligible decay of either the Q radical or V
Effective rate constants for hydroquinone autoxidation were
measured using a 1 cm flow cell (Optiglass Ltd, Essex, UK) and
absorbance changes measured using a Hewlett Packard 8452A
Diode Array Spectrophotometer. Irradiated samples and air or
oxygen-saturated solutions were mixed just before the mixing
cell via 20 cm3 hypodermic syringes and a capillary t-junction,
and passed through the flow cell to a stopping syringe in a
conventional arrangement. The absorbance changes at specific
wavelengths were monitored 0–500 s after mixing, with meas-
urements every 0.5–2 s. The effect of SOD on rates of hydro-
quinone autoxidation was studied by mixing irradiated samples
with SOD (∼4 µmol dmϪ3 after mixing) in oxygen-saturated
solutions containing 0.2 mmol dmϪ3 phosphate buffer at pH
7.4. All experiments were performed at ambient room
temperature (25 2 ЊC).
Ϫ
ؒ
+
ؒ
radical-cation via self-disproportionation reactions) and it was
possible to determine the equilibrium constant K from the
absorbance at equilibrium.28 One-electron reduction potentials
(E(Q/Q Ϫ)) for new indolequinones displayed in Table 2 are
ؒ
2+
+
quoted relative to E(BV /BV ) = Ϫ368 7 mV in 1 mol dmϪ3
ؒ
propan-2-ol, E(BV /BV ) = Ϫ374 7 mV in 0.2 mol dmϪ3
2+
+
ؒ
propan-2-ol, E(MV /MV ) = Ϫ450 7 mV in 0.2 mol dmϪ3
2+
+
ؒ
2+
+
ؒ
propan-2-ol and E(MV /MV ) = Ϫ448 7 mV in 0.7 mol
dmϪ3 propan-2-ol.29
The reactivity of semiquinone radicals with oxygen were
determined by gassing solutions with N2O–O2 mixtures (0.2–
Ϫ
ؒ
2.1% O2, British Oxygen Company, UK). At pH > 7 the Q
radical absorption monitored at 345 nm exhibited negligible
decay in the absence of oxygen up to 500 µs after an electron
Ϫ
ؒ
pulse of 1 Gy. In the presence of oxygen the Q radicals
decayed faster with increasing oxygen concentrations. Absolute
rate constants were determined from the slopes of the linear
plots of the observed first-order rate constants versus oxygen
concentration and are displayed in Table 3. The latter were
Chemical synthesis
Ethyl 3-amino-3-(2-naphthyl)propenoate. Ethyl (2-naphthoyl)-
acetate (4.6 g, 0.019 mol), ammonium acetate (14.6 g, 0.19
mol), benzene (150 cm3) and acetic acid (30 cm3) were refluxed
under Dean–Stark conditions for 24 h. The cooled reaction
mixture was washed with sodium hydrogen carbonate and the
benzene layer dried (Na2SO4) and concentrated. The crude
material was purified by column chromatography (70%
dichloromethane–30% light petroleum) to give the title com-
pound (3.2 g, 70%) as a pale yellow oil; νmax (film)/cmϪ1 3483,
3442, 3334, 3058, 2981, 1680, 1655, 1619; δH (300 MHz; CDCl3)
8.02 (1H, m), 7.87–7.83 (3H, m), 7.59 (1H, dd, J 8.6, J 1.8),
7.55–7.50 (2H, m), 5.12 (1H, s), 4.21 (2H, q, J 7.1), 1.33 (3H, t,
J 7.1); NH2 not observed; δC (100 MHz; CDCl3) 170.4, 160.4,
134.9, 134.1, 133.0, 128.6, 128.5, 127.7, 127.1, 126.8, 125.8,
123.6, 85.1, 59.0, 14.6; m/z (EI, relative intensity) 241 (M+,
40%), 196 (40), 169 (100); m/z (HRMS) 241.1088 (C15H15NO2
requires M 241.1103).
corrected for oxygen solubility in propan-2-ol (1–6.5 mol dmϪ3
)
from literature data.30
For measurements of the reductive elimination of 4-nitro-
phenol from indolequinones over longer timescales up to 10 s,
a solid-state light source was developed to minimise possible
sample photobleaching. The source uses a number of narrow-
band (15–30 nm) light-emitting diodes (LEDs) which cover the
range ∼430–900 nm. Thus 12 LEDs were positioned in front of
an optical fibre and positioning was achieved using a rotating
wheel servo system. The output end of the fibre was at the
focus of an aspheric lens, producing a highly collimated beam
to illuminate the sample cell. This novel system was utilised in
combination with the traditional tungsten lamp and photo-
diode detector to determine the rates of 4-nitrophenol release
displayed in Table 3. For indolequinones where the dispro-
portionation of semiquinone radicals could compete with
the release of 4-nitrophenol a simulated data fitting model
(FACSIMILE)31 provided estimates of rate constants from
experimental data.
General method for the preparation of the 5-hydroxyindole-3-
carboxylates 5 by the Nenitzescu reaction
(a) 1,4-Benzoquinone (5.5 mmol) and the aminoalkenoate (4.6
mmol) were refluxed for 1 h in acetic acid (50 cm3). The acetic
acid was removed in vacuo. The crude product was purified by
column chromatography (80% light petroleum–20% acetone)
and recrystallised (acetone–light petroleum) to yield the
product.
Steady-state ꢀ-radiolysis
HPLC analysis was carried out using indolequinone solutions
(50–100 µmol dmϪ3) which were saturated with N2O gas in
gas-tight vials before irradiation in a 60Co source. An absorbed
(b) Alternatively the reaction was carried out in nitromethane
dose of 1 Gy = 0.67 µmol dmϪ3 (CH3)2C OH radicals in N2O-
at room temperature as previously described.33
ؒ
J. Chem. Soc., Perkin Trans. 2, 2001, 843–860
851

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Table 4 Solvents used in HPLC analysis of indolequinones (Q)
Q
Aqueous buffer (mmol dmϪ3
)
Organic phase
Gradient (% organic phase)
37
KH2PO4 (5), H3PO4 (5)
KH2PO4 (5), H3PO4 (5)
KH2PO4 (5) H3PO4 (5)
KH2PO4 (5), H3PO4 (5)
KH2PO4 (5), H3PO4 (5)
KH2PO4 (5), H3PO4 (5)
KH2PO4 (5), H3PO4 (5)
KH2PO4 (5), H3PO4 (5)
KH2PO4 (5), H3PO4 (5)
75%MeCN
75%MeCN
75%MeCN
75%MeCN
75%MeCN
75%MeCN
75%MeCN
MeOH
50–95%, 6 min
35–80%, 8 min
50–95%, 6 min, hold 2.5 min
45–95%, 6 min
40–85%, 5 min
50–95%, 8 min, hold 1 min
45–90%, 5 min, hold 1 min
50–95%, 8 min
32, 33, 34
38, 45
36, 47
40, 48, 46
41, 49
50
39, 42, 43, 44
35
MeOH
40–85%, 5 min, hold 1 min
Methyl 5-hydroxy-1,2,6-trimethylindole-3-carboxylate 5a.
Prepared from 2-methyl-1,4-benzoquinone and methyl 3-
(methyl)aminobut-2-enoate in nitromethane as an inseparable
mixture which was used directly in the next step.
washed thoroughly with 1 mol dmϪ3 hydrochloric acid. The
organic layer was separated, dried (MgSO4) and concentrated.
The crude material was purified by column chromatography
(70% light petroleum–30% ethyl acetate) and recrystallised
(ethyl acetate–light petroleum) to yield the title compound as a
colorless crystalline solid.
Ethyl 5-hydroxy-2-(2-naphthyl)indole-3-carboxylate 5b. Pre-
pared from 1,4-benzoquinone and ethyl 3-amino-3-(2-
naphthyl)propenoate in acetic acid in 78% yield; mp 197–199 ЊC
(Found: C, 76.2; H, 5.2; N, 4.2. C21H17NO3 requires C, 76.1; H,
5.2; N, 4.2%); νmax (KBr disc)/cmϪ1 3377, 3323, 3049, 2985,
1666, 1628; δH (400 MHz; (CD3)2CO) 10.89 (1H, br s), 8.23 (1H,
d, J 1.0), 7.96–7.93 (4H, m), 7.86 (1H, dd, J 8.6, J 1.8), 7.72
(1H, d, J 2.4), 7.55 (2H, m), 7.35 (1H, dd, J 8.6, J 0.5), 6.85 (1H,
dd, J 8.6, J 2.4), 4.23 (2H, q, J 7.1), 1.22 (3H, t, J 7.1); δC (100
MHz; (CD3)2CO) 164.8, 152.9, 144.5, 133.4, 132.9, 130.6, 130.3,
129.3, 128.8, 128.2, 127.9, 127.6, 127.0, 126.6, 126.3, 112.8,
112.0, 106.2, 103.7, 58.8, 13.8; m/z (EI, relative intensity) 331
(M+, 95%), 286 (84), 259 (100); m/z (HRMS) 331.1208
(C21H17NO3 requires M 331.1208).
Methyl 5-methoxy-1,2,6-trimethylindole-3-carboxylate 6a.
(80%), mp 162–164 ЊC; νmax (CH2Cl2)/cmϪ1 1685; δH (300 MHz;
CDCl3) 7.55 (1H, s), 7.02 (1H, s), 3.99 (6H, s), 3.60 (3H, s), 2.70
(3H, s), 2.29 (3H, s); δC (75 MHz; CDCl3) 166.7, 154.2, 144.0,
131.1, 125.2, 122.3, 110.6, 103.3, 101.7, 55.7, 50.2, 29.6, 17.1,
12.0; m/z (EI, relative intensity) 247 (M+, 100%), 232 (64), 216
(34); m/z (HRMS) 247.1206 (C14H17NO3 requires M 247.1208).
Ethyl 5-methoxy-1-methyl-2-(2-naphthyl)indole-3-carboxylate
6b. (90%), mp 130–131 ЊC (Found: C, 76.6; H, 5.8; N, 3.8.
C23H21NO3 requires C, 76.9; H, 5.9; N, 3.9%); νmax (KBr disc)/
cmϪ1 3047, 3012, 2973, 2946, 2898, 2833, 1699, 1617, 1599;
δH (300 MHz; CDCl3) 8.00–7.88 (4H, m), 7.82 (1H, d, J 2.5),
7.59–7.50 (3H, m), 7.30 (1H, dd, J 8.8, J 0.3), 7.00 (1H, dd,
J 8.8, J 2.5), 4.16 (2H, q, J 7.1), 3.94 (3H, s), 3.58 (3H, s), 1.07
(3H, t, J 7.1); δC (100 MHz; CDCl3) 165.2, 156.0, 146.6, 133.3,
132.8, 132.1, 129.8, 129.2, 128.3, 128.0, 127.8, 127.6, 127.5,
126.8, 126.4, 113.2, 110.6, 105.2, 103.5, 59.2, 55.8, 31.1, 14.1;
m/z (EI, relative intensity) 359 (M+, 100%), 314 (40), 287 (38),
242 (21); m/z (HRMS) 359.1521 (C23H21NO3 requires M
359.1521).
Ethyl 5-hydroxy-2,6-dimethyl-1-phenylindole-3-carboxylate
5f. Prepared from 2-methyl-1,4-benzoquinone and ethyl 3-
(phenyl)aminobut-2-enoate in nitromethane as an inseparable
mixture which was used directly in the next step.
Ethyl
1-(4-fluorophenyl)-5-hydroxy-2-methylindole-3-carb-
oxylate 5g. Prepared from 1,4-benzoquinone and ethyl 3-(N-4-
fluorophenyl)aminobut-2-enoate in nitromethane in 22% yield;
mp 220–222 ЊC (Found: C, 67.3; H, 5.1; N, 4.4. C18H16FNO3ؒ
0.4 H2O requires C, 67.4; H, 5.3; N, 4.4%); νmax (CH2Cl2)/cmϪ1
3257, 1659; δH(300 MHz; (CD3)2SO) 7.54–7.42 (5H, m), 6.77
(1H, d, J 8.8), 6.64 (1H, dd, J 8.8, J 2.4), 4.34 (2H, d, J 7.0), 2.50
(3H, s), 1.37 (3H, t, J 7.0); OH not observed; δC (75 MHz;
(CD3)2SO) 165.1, 163.3 (d, JCF 246.2), 132.3 (d, JCF 2.9), 131.6,
130.3 (d, JCF 9.0), 127.1, 116.8 (d, JCF 22.9), 112.1, 110.7, 105.5,
103.7, 59.0, 14.2, 12.8; m/z (EI, relative intensity) 313 (M+,
43%), 268 (24), 241 (10), 83 (100), 58 (56); m/z (HRMS)
313.1116 (C18H16FNO3 requires M 313.1114).
Ethyl 1-cyclopropyl-5-methoxy-2-methylindole-3-carboxylate
6c. (72%), mp 114–116 ЊC (Found: C, 70.1; H, 7.0; N, 4.9.
C16H19NO3 requires C, 70.3; H, 7.0; N, 5.1%); νmax (CH2Cl2)/
cmϪ1 1679; δH (300 MHz; CDCl3) 7.64 (1H, d, J 2.6) 7.43 (1H,
d, J 8.8), 6.85 (1H, dd, J 8.8, J 2.6), 4.39 (2H, q, J 7.2), 3.88 (3H,
s), 3.15–3.08 (1H, m), 2.81 (3H, s), 1.45 (3H, t, J 7.2), 1.25–1.19
(2H, m), 1.03–0.97 (2H, m); δC (75 MHz; CDCl3) 166.0, 155.4,
147.4, 132.1, 127.2, 111.3, 111.2, 103.9, 103.4, 59.2, 55.6, 24.9,
14.5, 13.1, 7.5; m/z (EI, relative intensity) 273 (M+, 100%), 244
(78), 228 (43), 200 (28); m/z (HRMS) 273.1370 (C16H19NO3
requires M 273.1365).
Ethyl 5-hydroxy-2-methyl-1-propylindole-3-carboxylate 5h.
Prepared from 1,4-benzoquinone and ethyl 3-(propylamino)-
but-2-enoate in nitromethane in 47% yield; mp 180–182 ЊC
(lit.34 176–177 ЊC).
Methyl 1-benzyl-2-ethyl-5-methoxyindole-3-carboxylate 6d.
(90%), mp 114–116 ЊC (Found: C, 74.6; H, 6.7; N, 4.1. C20H21-
NO3 requires C, 74.3; H, 6.55; N, 4.33%); νmax (CH2Cl2)/cmϪ1
1687; δH (300 MHz; CDCl3) 7.53 (1H, d, J 2.6), 7.35 (1H, d,
J 8.8), 7.30–7.21 (3H, m), 6.98 (2H, dd, J 7.6, J 1.09), 6.81 (1H,
dd, J 8.8, J 2.6), 5.51 (2H, s), 3.84 (3H, s), 3.79 (3H, s), 3.11
(2H, q, J 7.3), 1.06 (3H, t, J 7.3); δC (75 MHz; CDCl3) 165.2,
155.3, 150.9, 137.6, 131.1, 128.8, 127.4, 127.0, 126.0, 111.5,
111.5, 103.4, 102.3, 55.4, 55.6, 45.9, 18.8, 13.9; m/z (EI, relative
intensity) 323 (M+, 86%), 292 (22), 200 (33), 91 (100); m/z
(HRMS) 323.1522 (C20H21NO3 requires M 323.1521).
Ethyl 5-hydroxy-2,6-dimethyl-1-propylindole-3-carboxylate
5i. Prepared from 2-methyl-1,4-benzoquinone and ethyl 3-
(propylamino)but-2-enoate in nitromethane in 52% yield; mp
195–198 ЊC (lit.35 193.5–195.0 ЊC)
General method for the synthesis of 5-methoxyindole-3-
carboxylates 6
To a stirring solution of the 5-hydroxyindole 5 (2.3 mmol) in
DMSO (15 cm3) was added potassium hydroxide (0.52 g, 9.3
mmol). After 30 min, iodomethane (1.30 g, 9.2 mmol) was
added drop-wise. The mixture was stirred at room temperature
for 3 h. The crude mixture was diluted with ethyl acetate and
Ethyl 5-methoxy-2-methyl-1-phenylindole-3-carboxylate 6e.
(82%), mp 87–88 ЊC; νmax (CH2Cl2)/cmϪ1 1680.23; δH (400 MHz;
CDCl3) 7.71 (1H, d, J 2.5), 7.57–7.53 (3H, m), 7.30–7.33 (2H,
m), 6.91 (1H, dd, J 8.8, J 0.5), 6.79 (1H, dd, J 8.8, J 2.5), 4.35
852
J. Chem. Soc., Perkin Trans. 2, 2001, 843–860

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(2H, q, J 7.1), 3.90 (3H, s), 2.57 (3H, s), 1.47 (3H, t, J 7.1); δC
(100 MHz; CDCl3) 166.2, 155.9, 145.4, 136.7, 132.8, 129.7,
128.7, 128.2 (2 × CH), 127.4, 112.1, 111.1, 104.9, 104.4, 59.4,
55.8, 14.6, 13.1; m/z (EI, relative intensity) 309 (M+, 28%), 152
(74), 84 (100), 55 (52); m/z (HRMS) 309.1370 (C19H19NO3
requires M 309.1364).
cmϪ1 1695, 1536; δH (300 MHz; CDCl3) 7.14 (1H, s), 3.84 (3H,
s), 3.78 (3H, s), 3.62 (3H, s), 2.64 (3H, s), 2.40 (3H, s); δC (75
MHz; CDCl3) 164.8, 146.7, 145.5, 138.2, 134.1, 126.6, 115.4,
112.9, 102.71, 62.7, 50.3, 29.9, 16.5, 11.9; m/z (EI, relative inten-
sity) 292 (M+, 43%), 215 (26), 69 (100); m/z (HRMS) 292.1061
(C14H16N2O5 requires M 292.1059).
Ethyl
5-methoxy-1-methyl-2-(2-naphthyl)-4-nitroindole-3-
Ethyl 5-methoxy-2,6-dimethyl-1-phenylindole-3-carboxylate
6f. (80%), mp 111–113 ЊC; νmax (CH2Cl2)/cmϪ1 1680; δH (300
MHz; CDCl3) 7.66 (1H, s), 7.60–7.48 (3H, m), 7.31 (2H, dd,
J 7.5, J 2.2), 6.78 (1H, s), 4.44 (2H, t, J 7.0), 3.94 (3H, s), 2.56
(3H, s), 2.25 (3H, s), 1.48 (3H, t, J 7.0); δC (75 MHz; CDCl3)
166.3, 154.5, 144.1, 136.8, 132.2, 129.7, 128.7, 128.2, 125.3,
122.8, 111.7, 104.8, 101.5, 59.4, 55.7, 16.94, 14.7, 13.1; m/z (EI,
relative intensity) 323 (M+, 100%), 308 (20), 278 (22); m/z
(HRMS) 323.1529 (C20H21NO3 requires M 323.1521).
carboxylate 7b. (74%), mp 217–219 ЊC (Found: C, 67.8; H, 4.9;
N, 6.7. C23H20N2O5 requires C, 68.3; H, 5.0; N, 6.9%); νmax (KBr
disc)/cmϪ1 3012, 2985, 2931, 1691, 1621, 1596; δH (300 MHz;
CDCl3) 7.93 (4H, m), 7.57 (2H, m), 7.48 (2H, m), 7.11 (1H, d,
J 9.0), 4.07 (2H, q, J 7.12), 3.98 (3H, s), 3.60 (3H, s), 0.98 (3H, t,
J 7.2); δC (75 MHz; CDCl3) 163.6, 148.6, 147.3, 133.4, 133.0,
132.6, 129.9, 128.3, 127.9, 127.9, 127.8, 127.4, 127.1, 126.7,
118.2, 112.6, 109.2, 104.7, 60.1, 57.8, 31.4, 13.7 (1 C not
observed); m/z (EI, relative intensity) 404 (M+, 10%), 149 (19),
105 (50), 44 (100); m/z (HRMS) 404.1372 (C23H20N2O5 requires
M 404.1372).
Ethyl 1-(4-fluorophenyl)-5-methoxy-2-methylindole-3-carb-
oxylate 6g. (70%), mp 113–115 ЊC; νmax (CH2Cl2)/cmϪ1 1683;
δH (300 MHz; CDCl3) 7.70 (1H, d, J 2.4), 7.32–7.22 (4H, m),
6.87 (1H, d, J 9), 6.79 (1H, dd, J 9, J 2.4), 4.42 (2H, q, J 7.0),
3.90 (3H, s), 2.56 (3H, s), 1.47 (3H, t, J 7.0); δC (75 MHz;
CDCl3) 166.1, 162.4 (d, JCF 249.2), 156.0, 145.4, 132.8, 132.6 (d,
JCF 3.3), 130.4, 130.0 (d, JCF 8.8), 127.3, 116.8 (d, JCF 22.8),
112.2, 110.9, 103.4, 59.5, 55.8, 14.6, 13.1; m/z (EI, relative inten-
sity) 327 (M+, 100%), 282 (33), 84 (38), 57 (38); m/z (HRMS)
327.1274 (C19H18FNO3 requires M 327.1270).
Ethyl 1-cyclopropyl-5-methoxy-2-methyl-4-nitroindole-3-carb-
oxylate 7c. (70%), mp 177–179 ЊC (Found: C, 58.9, H, 5.5, N,
9.1. C16H18N2O5ؒ0.5 H2O requires C, 58.7; H, 5.8; N, 8.8%);
νmax (CH2Cl2)/cmϪ1 1696, 1510; δH (300 MHz; CDCl3) 7.60 (1H,
d, J 9.0), 6.93 (1H, d, J 9.0), 4.27 (2H, q, J 7.2), 3.89 (3H, s),
3.18–3.11 (1H, m), 2.75 (3H, s), 1.34 (3H, t, J 7.2), 1.29–1.20
(2H, m), 0.93–0.90 (2H, m); δC (75 MHz; CDCl3) 164.5, 149.5,
146.9, 133.4, 133.3, 117.8, 113.4, 108.0, 103.3, 60.1, 57.7, 25.2,
14.2, 13.2, 7.8; m/z (EI, relative intensity) 318 (M+, 100%), 272
(19), 84 (26); m/z (HRMS) 318.1225 (C16H18N2O5 requires M
318.1216).
Ethyl 5-methoxy-2-methyl-1-propylindole-3-carboxylate 6h.
(68%), mp 88–89 ЊC (lit.36 87.5–88 ЊC).
Ethyl 5-methoxy-2,6-dimethyl-1-propylindole-3-carboxylate
6i. Ethyl 5-hydroxy-2,6-dimethyl-1-propylindole-3-carboxylate
(2.0 g, 7.3 mmol) in DMF (20 cm3) was added to a stirring
suspension of sodium hydride (0.34 g, 14.2 mmol) in DMF (30
cm3) at 0 ЊC. The mixture was stirred at room temperature for
45 min. Iodomethane (2.06 g, 14.5 mmol) was added drop-wise
at 0 ЊC and the mixture allowed to warm to room temperature.
After 2 h saturated ammonium chloride solution was added
and the mixture extracted with ethyl acetate. The ethyl acetate
layer was washed thoroughly with hydrochloric acid 1 mol
dmϪ3, dried (MgSO4) and concentrated. The crude product was
purified by column chromatography (10% ethyl acetate–hexane
elution) to yield the title compound as colourless needles
(1.69 g, 80%), mp 94–95 ЊC (from hexane) (Found: C, 70.7; H,
8.2; N, 4.8. C17H23NO3 requires C, 70.5; H, 8.0; N, 4.8%); νmax
(KBr disc)/cmϪ1 2971, 2935, 2894, 1685, 1572; δH (300 MHz;
CDCl3) 7.61 (1H, s), 7.04 (1H, s), 4.40 (2H, q, J 7.1), 4.01 (2H,
t, J 7.4), 3.91 (3H, s), 2.73 (3H, s), 2.35 (3H, s), 1.78 (2H, sextet,
J 7.4), 1.46 (3H, t, J 7.1), 0.96 (3H, t, J 7.4); δC (100 MHz;
CDCl3) 166.3, 154.1, 143.5, 130.5, 125.5, 122.2, 110.8, 103.5,
101.8, 59.2, 55.6, 44.8, 23.1, 17.1, 14.6, 12.0, 11.4; m/z (EI,
relative intensity) 290 (MH+, 100%).
Methyl 1-benzyl-2-ethyl-5-methoxy-4-nitroindole-3-carboxyl-
ate 7d. (70%), mp 178–180 ЊC (Found: C, 65.2; H, 5.4; N, 7.4.
C20H20N2O5 requires C, 65.2; H, 5.5; N, 7.6%); νmax (CH2Cl2)/
cmϪ1 1701, 1507; δH (300 MHz; CDCl3) 7.31–7.26 (3H, m), 7.21
(1H, d, J 9.0), 6.92 (2H, m), 6.88 (1H, d, J 9.0), 5.37 (2H, s),
3.87 (3H, s), 3.82 (3H, s), 3.11 (2H, q, J 7.2), 1.18 (3H, t, J 7.2);
δC (75 MHz; CDCl3) 164.5, 152.9, 147.1, 135.7, 133.8, 132.3,
129.1 (2 × CH), 128.0, 125.7, 118.1, 112.7, 108.5, 102.6, 57.7,
50.5, 46.8, 19.3, 13.8; m/z (EI, relative intensity) 368 (M+, 10%),
319 (2), 201 (3); m/z (HRMS) 368.1373 (C20H20N2O5 requires M
368.1372).
Ethyl 5-methoxy-2-methyl-4-nitro-1-phenylindole-3-carboxyl-
ate 7e. (75%), mp 129–131 ЊC; νmax (CH2Cl2)/cmϪ1 1696, 1516;
δH (400 MHz; CDCl3) 7.60–7.58 (3H, m), 7.30–7.04 (2H, m),
7.03 (1H, d, J 9.0), 6.89 (1H, d, J 9.0), 4.35 (2H, q, J 7.2), 3.92
(3H, s), 2.53 (3H, s), 1.39 (3H, t, J 7.2); δC (100 MHz; CDCl3)
164.6, 147.6, 147.4, 135.7, 133.8, 131.3, 130.0, 129.5, 128.2,
118.0, 113.1, 108.6, 104.2, 60.3, 57.8, 14.2, 13.1; m/z (EI, relative
intensity) 354 (M+, 100%), 263 (40), 221 (35), 77 (57); m/z
(HRMS) 354.1227 (C19H18N2O5 requires M 354.1216).
Ethyl 5-methoxy-2,6-dimethyl-4-nitro-1-phenylindole-3-carb-
oxylate 7f. (61%), mp 122–124 ЊC (Found: C, 64.9; H, 5.4; N,
7.6. C20H20N2O5 requires C, 65.2; H, 5.5; N, 7.6%); νmax
(CH2Cl2)/cmϪ1 1706, 1536; δH (300 MHz; CDCl3) 7.64–7.55
(3H, m), 7.28 (2H, dd, J 7.0, J 2.2), 6.88 (1H, s), 4.34 (2H, q,
J 7.0), 3.88 (3H, s), 2.51 (3H, s), 2.34 (3H, s), 1.39 (3H, t, J 7.0);
δC (75 MHz; CDCl3) 164.6, 146.9, 146.10, 138.2, 135.7, 135.3,
130.1, 129.5, 128.2, 127.3, 115.6, 114.2, 104.3, 62.7, 60.3, 16.5,
14.2, 13.1; m/z (EI, relative intensity) 368 (M+, 1%), 295 (8), 149
(37), 84 (60), 69 (100); m/z (HRMS) 368.1379 (C20H20N2O5
requires M 368.1372).
General method for nitration
To a solution of indole 6 (2.06 mmol) in acetic acid (10 cm3),
cooled to Ϫ10 ЊC was added a mixture of nitric acid (0.14 cm3)
and acetic acid (0.54 cm3). The mixture was stirred at room
temperature for 2 h. A yellow suspension was obtained which
was poured on to an ice–water mixture and the crystals
obtained were filtered off and dried. The crude product was
purified by column chromatography (50% dichloromethane–
50% ethyl acetate) to yield the 4-nitro (major) and 6-nitro
(minor) compounds. Spectroscopic data are given for the
required 4-nitro isomer.
Ethyl 1-(4-fluorophenyl)-5-methoxy-2-methyl-4-nitroindole-3-
carboxylate 7g. (60%), mp 153–155 ЊC; νmax (CH2Cl2)/cmϪ1
1700, 1512; δH (300 MHz; CDCl3) 7.32–7.26 (4H, m), 7.0 (1H,
d, J 9.0), 6.89 (1H, d, J 9.0), 4.32 (2H, q, J 7.0), 3.90 (3H, s),
Methyl 5-methoxy-1,2,6-trimethyl-4-nitroindole-3-carboxyl-
ate 7a. (65%), mp 174–176 ЊC (Found: C, 57.1; H, 5.4; N, 9.6.
C14H16N2O5 requires C, 57.5; H, 5.5; N, 9.6%); νmax (CH2Cl2)/
J. Chem. Soc., Perkin Trans. 2, 2001, 843–860
853

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2.51 (3H, s), 1.37 (3H, t, J 7.0); δC (75 MHz; CDCl3) 162.8 (d,
JCF 249.6), 147.6, 147.4, 133.8, 131.6 (d, JCF 3.2), 131.2, 130.0
(d, JCF 8.9), 117.9, 117.2 (d, JCF23.0), 113.0, 108.7, 104.6, 104.3,
60.3, 57.7, 14.2, 13.1.
t, J 7.2), 1.24–1.18 (2H, m), 1.0–0.95 (2H, m); δC (75 MHz;
CDCl3) 167.0, 146.1, 141.0, 134.5, 131.1, 114.3, 109.4, 104.8,
98.2, 60.1, 57.6, 25.1, 14.5, 14.3, 8.0; m/z (EI, relative intensity),
288 (M+, 41%), 263 (100), 227 (52), 83 (96); m/z (HRMS)
288.1466 (C16H20N2O3 requires M 288.1474)
Ethyl 5-methoxy-2-methyl-4-nitro-1-propylindole-3-carboxyl-
ate 7h. (72%), mp 162–164 ЊC (Found: C, 59.9; H, 6.3; N, 8.7.
C16H20N2O5 requires C, 60.0; H, 6.3; N, 8.7%); νmax (KBr disc)/
cmϪ1 3093, 2975, 2929, 2903, 1695; δH (300 MHz; CDCl3) 7.34
(1H, d, J 9.0), 6.95 (1H, d, J 9.0), 4.30 (2H, q, J 7.1), 4.07 (2H, t,
J 7.4), 3.92 (3H, s), 2.70 (3H, s), 1.76 (2H, sextet, J 7.4), 1.36
(3H, t, J 7.1), 0.96 (3H, t, J 7.4); δC (100 MHz; CDCl3) 164.6,
146.93, 146.91, 133.7, 132.2, 118.0, 111.9, 108.2, 103.2, 60.1,
57.8, 45.1, 23.0, 14.1, 12.0, 11.3; m/z (EI, relative intensity) 343
(M + Na, 100%), 275 (26).
Methyl
4-amino-1-benzyl-2-ethyl-5-methoxyindole-3-carb-
oxylate 8d. (75%), mp 150–152 ЊC (Found: C, 70.4; H, 6.6; N,
8.1. C20H22N2O3 requires C, 70.1; H, 6.6; N, 8.3%); νmax
(CH2Cl2)/cmϪ1 3329–3432, 1675; δH (400 MHz; CDCl3) 7.27–
7.25 (3H, m), 6.98–6.95 (2H, m), 6.83 (1H, d, J 8.8), 6.45 (1H, d,
J 8.8), 5.73 (2H, br s), 5.28 (2H, s), 3.91 (3H, s), 3.86 (3H, s),
3.02 (2H, q, J 7.2), 1.16 (3H, t, J 7.2); δC (100 MHz; CDCl3)
167.3, 149.6, 141.4, 136.7, 133.7, 130.8, 128.9, 127.5, 125.8,
114.8, 109.9, 103.9, 97.5, 57.5, 51.3, 46.6, 20.1, 14.1; m/z (EI,
relative intensity) 338 (M+, 52%), 291 (27), 83 (100); m/z
(HRMS) 338.1630 (C20H22N2O3 requires M 338.1630).
Ethyl 5-methoxy-2,6-dimethyl-4-nitro-1-propylindole-3-carb-
oxylate 7i. (60%), mp 99–101 ЊC (Found: C, 60.7; H, 6.6; N, 8.6.
C17H22N2O5 requires C, 61.0; H, 6.6; N, 8.4%); νmax (KBr disc)/
cmϪ1 3416, 3324, 2980, 2924, 1695, 1659, 1602; δH (300 MHz;
CDCl3) 7.20 (1H, s), 4.30 (2H, J 7.1), 4.05 (2H, t, J 7.4), 3.88
(3H, s), 2.71 (3H, s), 2.45 (3H, s), 1.77 (2H, sextet, J 7.4), 1.37
(3H, t, J 7.1), 0.98 (3H, t, J 7.5); δC (100 MHz; CDCl3) 164.6,
146.2, 145.6, 138.3, 133.6, 126.5, 115.7, 113.1, 103.3, 62.6, 60.0,
45.0, 22.9, 16.6, 14.2, 12.0, 11.3; m/z (EI, relative intensity) 335
(MH+, 43%), 263 (40), 241 (100).
Ethyl
4-amino-5-methoxy-2-methyl-1-phenylindole-3-carb-
oxylate 8e. (80%), mp 161–162 ЊC (Found: C, 68.4; H, 5.9; N,
8.3. C19H20N2O3ؒ0.5 H2O requires C, 68.4; H, 6.4; N, 8.4%);
νmax (CH2Cl2)/cmϪ1 3472–3329, 1700; δH (400 MHz; CDCl3)
7.57–7.47 (2H, m), 7.30–7.26 (3H, m), 6.78 (1H, d, J 8.8), 6.19
(1H, d, J 8.8), 5.81 (2H, br s), 4.39 (2H, q, J 7.0), 3.86 (3H, s),
2.46 (3H, s), 1.42 (3H, t, J 7.0); δC (100 MHz; CDCl3) 167.1,
144.1, 141.2, 137.0, 135.2, 131.0, 129.7, 128.7, 128.6, 114.4,
109.8, 105.6, 97.9, 60.2, 57.6, 14.5, 14.3; m/z (EI, relative inten-
sity) 324 (M+, 65%), 309 (28), 263 (100), 77 (14); m/z (HRMS)
324.1470 (C19H20N2O3 requires M 324.1474).
General method for reduction of the nitro group
To a suspension of the 4-nitroindole 7 (1.16 mmol) in ethanol
(30 cm3) were added tin powder (0.62 g, 5.21 mmol) and hydro-
chloric acid (3.0 mol dmϪ3, 9 cm3). The mixture was refluxed for
30 min. Upon cooling the solution was decanted from the
excess tin and neutralized with saturated aqueous sodium
hydrogen carbonate. The suspension obtained was added to an
equal volume of water. The precipitate and aqueous layer were
stirred overnight with dichloromethane, and filtered through
Celite and the layers separated. The organic layer was dried
(Na2SO4) and concentrated. The crude product was purified
by column chromatography (80% light petroleum–20% ethyl
acetate) and recrystallised (light petroleum–ethyl acetate).
Ethyl
4-amino-5-methoxy-2,6-dimethyl-1-phenylindole-3-
carboxylate 8f. (60%), mp 125–127 ЊC; νmax (CH2Cl2)/cmϪ1
3473–3340, 1675; δH (400 MHz; CDCl3) 7.59–7.48 (3H, m),
7.29–7.26 (2H, m), 6.04 (1H, s), 5.85 (2H, br s), 4.38 (2H, q,
J 7.2), 3.76 (3H, s), 2.43 (3H, s), 2.26 (3H, s), 1.41 (3H, t, J 7.2);
δC (100 MHz; CDCl3) 167.2, 143.3, 140.0, 137.0, 136.0, 133.3,
129.7, 128.8, 128.6, 126.9, 113.1, 105.8, 100.1, 60.3, 59.1, 16.5,
14.5, 14.1; m/z (EI, relative intensity) 338 (M+, 25%), 277 (49),
83 (100); m/z (HRMS) 338.1635 (C20H22N2O3 requires M
338.1630).
Ethyl 4-amino-1-(4-fluorophenyl)-5-methoxy-2-methylindole-
3-carboxylate 8g. (65%), mp 121–123 ЊC (Found: C, 66.5; H,
5.6; N, 7.8. C19H19FN2O3 requires C, 66.7; H, 5.6; N, 8.2%); νmax
(CH2Cl2)/cmϪ1 3452–3324, 1672; δH (400 MHz; CDCl3) 7.26–
7.21 (4H, m), 6.78 (1H, d, J 8.6), 6.16 (1H, d, J 8.6), 5.78 (2H,
br s), 4.39 (2H, q, J 7.2), 3.86 (3H, s), 2.44 (3H, s), 1.42 (3H, t,
J 7.2); δC (100 MHz; CDCl3) 167.0. 162.4 (d, JCF 249.2), 144.0,
141.3, 135.3, 133.0, 131.0, 130.4 (d, JCF 8.8), 116.7 (d, JCF 22.6),
114.3, 109.8, 105.8, 97.6, 60.3, 57.5, 14.4, 14.2; m/z (EI, relative
intensity) 342 (M+, 40%), 327 (15), 281 (26) 83 (100); m/z
(HRMS) 342.1382 (C19H19FN2O3 requires M 342.1380).
Methyl 4-amino-5-methoxy-1,2,6-trimethylindole-3-carboxyl-
ate 8a. (80%), mp 169–171 ЊC; νmax (CH2Cl2)/cmϪ1 3473–3334,
1675; δH (300 MHz; CDCl3) 6.38 (1H, s), 5.78 (2H, s), 3.88 (3H,
s), 3.76 (3H, s), 3.54 (3H, s), 2.60 (3H, s), 2.38 (3H, s) δC (75
MHz; CDCl3) 167.4, 143.1, 139.6, 134.8, 133.9, 126.5, 113.0,
104.3, 98.5, 59.1, 51.2, 29.9, 16.7, 12.9; m/z (EI, relative inten-
sity) 262 (M+, 41%), 247 (37), 215 (100); m/z (HRMS) 262.1323
(C14H18N2O3 requires M 262.1317).
Ethyl 4-amino-5-methoxy-1-methyl-2-(2-naphthyl)indole-3-
carboxylate 8b. (64%), mp 165–167 ЊC (Found: C, 73.6; H, 5.9;
N, 7.5. C23H22N2O3 requires C, 73.8; H, 5.9; N, 7.5%); νmax (KBr
disc)/cmϪ1 3479, 3312, 2974, 2931, 2899, 2845, 1659, 1595;
δH (300 MHz; CDCl3) 7.94–7.86 (3H, m), 7.81 (1H, s), 7.56 (2H,
m), 7.43 (1H, dd, J 8.4, J 1.6), 7.00 (1H, d, J 8.7), 6.63 (1H, d,
J 8.7), 5.87 (2H, br s), 3.91 (5H, m), 3.44 (3H, s), 0.59 (3H, t,
J 7.1); δC (75 MHz; CDCl3) 166.6, 146.2, 141.1, 134.3, 133.0,
132.7, 131.7, 130.6, 129.4, 128.1, 127.9, 127.8, 127.4, 126.7,
126.5, 114.6, 110.7, 105.8, 96.8, 59.7, 57.7, 31.2, 13.4; m/z (EI,
relative intensity) 374 (M+, 74%), 314 (23), 313 (100); m/z
(HRMS) 3374.1630 (C23H22N2O3 requires 374.1630).
Ethyl
4-amino-5-methoxy-2-methyl-1-propylindole-3-carb-
oxylate 8h. (88%), mp 105–107 ЊC (Found: C, 66.1; H, 7.7; N,
9.5. C16H22N2O3 requires C, 66.2; H, 7.6; N, 9.6%); νmax (KBr
disc)/cmϪ1 3457, 3308, 2929, 2868, 2817, 1674, 1602; δH (400
MHz; CDCl3) 6.86 (1H, d, J 8.7), 6.54 (1H, d, J 8.7), 5.77 (2H,
br s), 4.37 (2H, q, J 7.1), 3.97 (2H, t, J 7.4), 3.87 (3H, s), 2.64
(3H, s), 1.76 (2H, sextet, J 7.4), 1.41 (3H, t, J 7.1), 0.95 (3H, t,
J 7.4); δH (100 MHz; CDCl3) 167.0, 143.4, 140.9, 133.4, 131.2,
114.7, 109.6, 104.4, 96.7, 60.0, 57.6, 44.9, 22.7, 14.5, 13.0, 11.4;
m/z (CI, relative intensity) 291 (MH+, 100%).
Ethyl
4-amino-1-cyclopropyl-5-methoxy-2-methylindole-3-
Ethyl
4-amino-5-methoxy-2,6-dimethyl-1-propylindole-3-
carboxylate 8c. (70%), mp 140–142 ЊC (Found: C, 66.2; H, 7.0;
N, 9.6. C16H20N2O3 requires C, 66.6; H, 7.0; N, 9.7%);
νmax (CH2Cl2)/cmϪ1 3334–3462, 1670; δH (300 MHz; CDCl3)
6.86 (1H, d, J 8.6), 6.81 (1H, d, J 8.6), 5.73 (2H, br s), 4.36 (2H,
q, J 7.2), 3.87 (3H, s), 3.08–3.02 (1H, m), 2.73 (3H, s), 1.41 (3H,
carboxylate 8i. (82%), mp 86–88 ЊC (Found: C, 67.1; H, 8.1; N,
9.2. C17H24N2O3 requires C, 67.1; H, 8.0; N, 9.2%); νmax (KBr
disc)/cmϪ1 3416, 3324, 2980, 2924, 1695, 1659, 1602; δH (400
MHz; CDCl3) 6.39 (1H, s), 5.06 (2H, br s), 4.36 (2H, q, J 7.1),
3.95 (2H, t, J 7.5), 3.76 (3H, s), 2.63 (3H, s), 2.38 (3H, s), 1.76
854
J. Chem. Soc., Perkin Trans. 2, 2001, 843–860

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(2H, sextet, J 7.5), 1.41 (3H, t, J 7.1), 0.97 (3H, t, J 7.5); δC (100
MHz; CDCl3) 167.0, 142.5, 139.5, 134.2, 133.9, 126.3, 113.2,
104.7, 98.8, 60.0, 59.0, 44.8, 22.8, 16.7, 14.5, 12.9, 11.4; m/z (ES,
relative intensity) 305 (MH+, 26%), 219 (100).
3-Hydroxymethyl-1,2-dimethyl-5-(morpholin-1-yl)indole-4,7-
dione 17. Prepared as previously described.13
3-Hydroxymethyl-5-methoxy-1-methyl-2-phenylindole-4,7-
dione 18. Prepared as previously described.13
Ethyl 5-methoxy-2,6-dimethyl-1-propyl-4,7-dioxoindole-3-
carboxylate 9
2-(Biphenyl-4-yl)-3-hydroxymethyl-5-methoxy-1-methyl-
indole-4,7-dione 19. Prepared as previously described.13
To a solution of the ethyl 4-amino-5-methoxy-2,6-dimethyl-1-
propylindole-3-carboxylate (0.03 g, 0.098 mmol) in acetone (10
cm3) was added a solution of potassium nitrosodisulfonate
(0.079 g, 0.29 mmol) in sodium dihydrogen phosphate buffer
(0.3 mol dmϪ3, 10 cm3). The mixture was stirred at room tem-
perature for 1 h. The excess acetone was removed in vacuo. The
resulting residue was extracted with dichloromethane and
washed with water. The organic layer was dried (Na2SO4) and
concentrated. The crude product was purified by column
chromatography (column 50% ethyl acetate–50% hexane elu-
tion) to yield the title compound as an orange solid (0.03 g,
96%), mp 75–76 ЊC (from hexane) (Found: C, 63.7; H, 6.6; N,
4.2. C17H21NO5 requires C, 63.9; H, 6.6; N, 4.4%); λmax
(MeOH)/nm 440 (log ε 2.97), 332 (3.61), 288 (4.13); νmax (KBr
disc)/cmϪ1 2986, 2950, 1732, 1671, 1640, 1609; δH (300 MHz;
CDCl3) 4.37 (2H, q, J 7.1), 4.26 (2H, m), 4.01 (3H, s), 2.43 (3H,
s), 1.94 (3H, s), 1.71 (2H, sextet, J 7.4), 1.39 (3H, t, J 7.1), 0.97
(3H, t, J 7.4); δC (100 MHz; CDCl3) 179.3, 177.2, 164.4, 16.6,
140.4, 128.9, 127.2, 122.5, 113.0, 61.0, 60.8, 46.9, 23.6, 14.1,
11.0, 10.6, 8.5; m/z (CI, relative intensity) 320 (MH+, 100%).
3-Hydroxymethyl-5-methoxy-1-methyl-2-(2-naphthyl)indole-
4,7-dione 20. (73%), mp 223–225 ЊC (Found: C, 72.4; H, 4.8; N,
4.1. C21H17NO4 requires C, 72.6; H, 4.9; N, 4.0%); λmax
(MeOH)/nm 454 (log ε 3.39), 350 (3.62), 274 (4.45); νmax (KBr
disc)/cmϪ1 3404, 3060, 2953, 2840, 1675, 1636, 1597; δH (400
MHz; CDCl3) 7.93 (3H, m), 7.81 (1H, m), 7.61–7.55 (2H, m),
7.39 (1H, dd, J 8.4, J 1.7), 5.75 (1H, s), 4.56 (2H, d, J 7.2), 4.08
(1H, t, J 7.2), 3.87 (3H, s), 3.83 (3H, s); δC (100 MHz; CDCl3)
179.3, 178.9, 156.0, 139.2, 133.3, 133.0, 130.5, 130.0, 128.7,
128.2, 127.9, 127.3, 127.2, 127.0, 125.6, 124.3, 122.2, 107.4,
56.7, 56.2, 34.2; m/z (EI, relative intensity) 347 (M+, 100%), 346
(67), 331 (28), 286 (26), 189 (29), 165 (32); m/z (HRMS)
347.1156 (C21H17NO4 requires 347.1157).
1-Cyclopropyl-3-hydroxymethyl-5-methoxy-2-methylindole-
4,7-dione 21. (60%), mp 217–219 ЊC (Found: C, 64.1; H, 5.8; N,
5.0. C14H15NO4 requires C, 64.4; H, 5.8; N, 5.4%); λmax
(MeOH)/nm 454 (log ε 3.34), 346 (3.57), 286 (4.35); νmax
(CH2Cl2)/cmϪ1 3429, 1638, 1601; δH (400 MHz; CDCl3) 5.61
(1H, s), 4.56 (2H, d, J 7.0), 3.99 (1H, t, J 7.0), 3.79 (3H, s), 3.17–
3.09 (1H, m), 2.32 (3H, s), 1.28–1.21 (2H, m), 0.86–0.80 (2H,
m); δC (100 MHz; CDCl3) 179.5, 177.0, 159.0, 136.8, 130.9,
122.5, 122.3, 107.5, 56.5, 55.7, 27.9, 11.2, 10.0; m/z (EI, relative
intensity) 261 (M+, 100%), 246 (47), 220 (10); m/z (HRMS)
261.0993 (C14H15NO4 requires M 261.1001).
General method for the preparation of 3-hydroxymethylindole-
4,7-diones
To a suspension of lithium aluminum hydride (0.079 g, 2.08
mmol) in tetrahydrofuran (30 cm3) at 0 ЊC was added a solution
of 4-aminoindole-3-ester 8 (0.52 mmol) in tetrahydrofuran (15
cm3). The reaction was allowed to warm to room temperature
and stirred for 30 min. The mixture was cooled to 0 ЊC and
quenched by the addition of water (0.5 cm3), sodium hydroxide
(1.0 mol dmϪ3, 0.5 cm3) and silica gel (5 g). The granular pre-
cipitate was filtered off through a pad of Celite. The filtrate was
dried (MgSO4) and concentrated in vacuo to give the alcohol
which was used directly in the next step without purification, or
characterization. To a solution of indole in acetone (20 cm3)
was added a solution of potassium nitrosodisulfonate (0.70 g,
2.6 mmol) in sodium dihydrogen phosphate buffer (0.3 mol
dmϪ3, 20 cm3). The mixture was stirred at room temperature for
1 h. The excess acetone was removed in vacuo. The resulting
residue was extracted with dichloromethane and washed with
water. The organic layer was dried (Na2SO4) and concentrated.
The crude product was purified by column chromatography
(5% ethyl acetate–95% dichloromethane) and recrystallised
(ethyl acetate–light petroleum).
1-Benzyl-2-ethyl-3-hydroxymethyl-5-methoxyindole-4,7-dione
22. (65%), mp 117–119 ЊC (Found: C, 69.9; H, 5.9; N, 4.1.
C19H19NO4 requires C, 70.1; H, 5.9; N, 4.3%); λmax (MeOH)/nm
462 (log ε 3.30), 344 (3.48), 286 (4.31); νmax (CH2Cl2)/cmϪ1 3454,
1639, 1602; δH (400 MHz; CDCl3) 7.30–7.20 (3H, m), 7.00–6.98
(2H, m), 5.63 (2H, s), 5.61 (1H, s), 4.62 (2H, d, J 7.0), 4.07 (1H,
t, J 7.0), 3.80 (3H, s), 2.56 (2H, q, J 7.0), 0.98 (3H, t, J 7.0);
δC (100 MHz; CDCl3) 179.5, 178.3, 159.5, 146.6, 136.3, 129.0,
128.8, 127.7, 126.1, 122.9, 122.6, 107.4, 56.6, 55.7, 48.3,
17.1.14.6; m/z (EI, relative intensity) 325 (M+, 38%), 234 (66),
91 (100); m/z (HRMS) 325.1312 (C19H19NO2 requires M
325.1314).
3-Hydroxymethyl-5-methoxy-2-methyl-1-phenylindole-4,7-
dione 23. (68%), mp 270–272 ЊC (Found: C, 67.0; H, 4.9; N, 4.4.
C17H15NO4ؒ0.4 H2O requires C, 67.0; H, 5.2; N, 4.6%); λmax
(MeOH)/nm 450 (log ε 3.28), 344 (3.48), 286 (4.31); νmax
(CH2Cl2)/cmϪ1 3462, 1653, 1646; δH (400 MHz; CDCl3) 7.53–
7.50 (3H, m), 7.24–7.19 (2H, m), 5.56 (1H, s), 4.68 (2H, d,
J 7.0), 4.06 (1H, t, J 7.0), 3.81 (3H, s), 2.01 (3H, s); δC (100
MHz; CDCl3) 179.8, 176.9, 159.5, 136.9, 135.3, 130.4, 129.4,
129.3, 127.1, 122.6, 122.4, 107.1, 56.6, 56.0, 10.1; m/z (EI,
relative intensity) 297 (M+, 38%), 282 (18), 84 (100), 77 (21);
m/z (HRMS) 297.0998 (C17H15NO4 requires M 297.1001).
3-Hydroxymethyl-5-methoxy-1-methylindole-4,7-dione
13.
Prepared as previously described.37
7-Methoxy-9-hydroxymethyl-2,3-dihydro-1H-pyrrolo[1,2-a]-
indole-5,8-dione 14. Prepared as previously described.13
3-Hydroxymethyl-5-methoxy-1,2-dimethylindole-4,7-dione
15. Prepared as previously described.13,38
3-Hydroxymethyl-5-methoxy-2,6-dimethyl-1-phenylindole-
4,7-dione 24. (65%), mp 135–137 ЊC; λmax (MeOH)/nm 460 (log
ε 3.04), 342 (3.64), 286 (4.23); νmax (CH2Cl2)/cmϪ1 3417, 1637,
1612; δH (300 MHz; CDCl3) 7.53–7.50 (3H, m), 7.21–7.18 (2H,
m), 4.67 (2H, d, J 7.0), 4.23 (1H, t, J 7.0), 3.99 (3H, s), 2.07 (3H,
s), 1.77 (3H, s); δC (100 MHz; CDCl3) 181.4, 177.4, 156.0, 137.1,
135.4, 130.1, 130.0, 129.4, 129.3, 127.1, 123.0, 122.4, 61.1, 56.0,
10.1, 8.8; m/z (EI, relative intensity) 311 (M+, 100%), 296 (69),
222 (15), 118 (22), 77 (71); m/z (HRMS) 311.1156 (C18H17NO4
requires M 311.1157).
3-Hydroxymethyl-5-methoxy-1,2,6-trimethylindole-4,7-dione
16. (68%), mp 163–165 ЊC; λmax (MeOH)/nm 465 (log ε 2.37),
350 (2.79), 288 (3.41); νmax (CH2Cl2)/cmϪ1 2948, 1637, 1638;
δH (400 MHz; CDCl3) 4.60 (2H, d, J 7.0), 4.19 (1H, t, J 7.0),
3.98 (3H, s), 3.87 (3H, s), 2.22 (3H, s), 1.97 (3H, s); δC (100
MHz; CDCl3) 181.0, 178.9, 156.0, 134.7, 129.8, 122.6, 122.4,
114.0, 61.1, 56.0, 32.4, 9.6, 8.90; m/z (EI, relative intensity) 249
(M+, 100%), 234 (62), 56 (56); m/z (HRMS) 249.1001
(C13H15NO4 requires M 249.1001).
J. Chem. Soc., Perkin Trans. 2, 2001, 843–860
855

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1-(4-Fluorophenyl)-3-hydroxymethyl-5-methoxy-2-methyl-
indole-4,7-dione 25. (66%), mp 265–267 ЊC; λmax (MeOH)/nm
454 (log ε 3.20), 344 (3.40), 286 (4.22); νmax (CH2Cl2)/cmϪ1 3436,
1647, 1607; δH (400 MHz; CDCl3) 7.20–7.18 (4H, m), 5.55
(1H, s), 4.66 (2H, d, J 7.0), 4.03 (1H, t, J 7.0), 3.80 (3H, s), 2.00
(3H, s); δC (100 MHz; CDCl3) 179.7, 176.9, 162.7 (d, JCF 249.7),
159.5, 135.3, 132.8 (d, JCF 3.4), 130.4, 128.9 (d, JCF 8.9), 122.6,
122.5, 116.5 (d, JCF 23.1), 107.1, 56.6, 55.9, 10.1; m/z (EI,
relative intensity) 315 (M+, 34%), 300 (18), 277 (51), 84 (100);
m/z (HRMS) 315.0909 (C17H14FNO4 requires M 315.0907).
3-Benzoyl-5-methoxy-2-methylindole 10b. (19%), mp 185–
186 ЊC; δH (60 MHz; CDCl3) 6.65–7.57 (8H, m), 3.63 (3H, s),
2.42 (3H, s).
5-Methoxy-2-methyl-3-(2-thienylcarbonyl)indole 10c. (46%),
mp 198–200 ЊC; δH (60 MHz; CDCl3) 6.63–7.88 (6H, m), 3.69
(3H, s), 2.5 (3H, s).
General method for the preparation of 3-acyl-5-nitroindoles 11
The crude 3-acylindole (12.3 mmol) was added to a stirred sus-
pension of sodium hydride (60% dispersion in oil, 26 mmol) in
tetrahydrofuran (anhydrous, 50 cm3). The solution was stirred
for 0.5 h at 50 ЊC, cooled and iodomethane (15 cm3, 105 mmol)
added. The solution was heated under reflux for 1 h, cooled and
added to a cold solution of sodium bisulfate (10%, 50 cm3). The
solution was extracted with ethyl acetate (150 cm3), washed
with saturated sodium bicarbonate solution (100 cm3) and
evaporated. The residue was purified by column chromato-
graphy (ethyl acetate–hexane, 1 : 1) to yield the N-methyl
derivative. This material (2.3 mmol) was then dissolved in
glacial acetic acid (7.5 cm3) and cooled to 0–4 ЊC. Fuming nitric
acid (1.5 cm3) in acetic acid (4.5 cm3) was then added slowly
with stirring at 0–4 ЊC. After 1 h crushed ice (50 g) was added
and the solution stirred for 0.5 h. The resulting pale yellow solid
was filtered, washed with water and dried in a vacuum oven at
45 ЊC over potassium hydroxide pellets for 12 h to give the
title compound.
3-Hydroxymethyl-5-methoxy-2-methyl-1-propylindole-4,7-
dione 26. (39%), mp 156–158 ЊC (Found: C, 62.3; H, 6.3; N, 4.9.
C14H17NO4ؒ0.4 H2O requires C, 62.1; H, 6.6; N, 5.2%); λmax
(MeOH)/nm 460 (log ε 3.18), 352 (3.39), 280 (4.00); νmax (KBr
disc)/cmϪ1 3400, 3053, 2960, 2919, 1676, 1650, 1592; δH (300
MHz; CDCl3) 5.60 (1H, s), 4.60 (2H, d, J 6.5), 4.23 (2H, t,
J 7.4), 4.08 (1H, br t), 3.81 (3H, s), 2.23 (3H, s), 1.70 (2H, sextet,
J 7.4), 0.95 (3H, t, J 7.4); δC (100 MHz; CDCl3) 179.3, 178.2,
159.5, 134.0, 129.0, 122.9, 122.2, 107.2, 56.5, 55.9, 46.8, 23.6,
11.0, 9.4; m/z (EI, relative intensity) 263 (M+, 65%), 248 (50),
221 (91), 206 (100).
3-(Hydroxymethyl)-5-methoxy-2,6-dimethyl-1-propylindole-
4,7-dione 27. To a solution of ethyl 5-methoxy-2,6-dimethyl-1-
propyl-4,7-dioxoindole-3-carboxylate 9 (0.31 g, 0.98 mmol) in
water–dichloromethane–ethanol (20 cm3) was added sodium
dithionite (1.7 g, 9.7 mmol) and the mixture stirred over-
night. The organic layer was separated, washed with saturated
ammonium chloride, dried (Na2SO4) and concentrated, and
used directly in the next step. To a stirred suspension of the
crude dihydroxyindole in dichloromethane (30 cm3) was added
DIBAL (1 mol dmϪ3 solution in hexane, 1.38 g, 9.7 mmol) at
Ϫ10 ЊC and the mixture was allowed to warm to 0 ЊC for 2 h.
The reaction was quenched by drop-wise addition of iron()
chloride (1 mol dmϪ3 in 0.1 mol dmϪ3 hydrochloric acid, 30
cm3). The crude mixture was purified by column chromato-
graphy (1 : 1, hexane–ethyl acetate) to yield the title compound
(0.103 g, 38%) as a red crystalline material, mp 81–83 ЊC (from
hexane) (Found: C, 64.8; H, 6.9; N, 4.8. C15H19NO4 requires C,
65.0; H, 6.9; N, 5.0%); λmax (MeOH)/nm 468 (log ε 3.08), 352
(3.52), 288 (4.14); νmax (KBr disc)/cmϪ1 3457, 2969, 2942, 1633,
1606, 1503; δH (300 MHz; CDCl3) 4.60 (2H, d, J 7.0), 4.23 (3H,
m), 3.98 (3H, s), 2.23 (3H, s), 1.97 (3H, s), 1.71 (2H, sextet,
J 7.4), 0.97 (3H, t, J 7.4); δC (100 MHz; CDCl3) 181.1, 178.4,
156.0, 134.2, 129.8, 128.8, 122.8, 122.7, 61.0, 56.0, 46.9, 23.6,
11.1, 9.5, 8.9; m/z (CI, relative intensity) 278 (MH+, 89),
277 (M+, 47), 262 (100), 260 (39); m/z (HRMS) 277.1313
(C15H19NO4 requires 277.1314).
3-Acetyl-1,2-dimethyl-5-methoxy-4-nitroindole 11a. 3-Acetyl-
1,2-dimethyl-5-methoxyindole (80%), mp 123–124 ЊC; δH (60
MHz; (CD3)2SO–CDCl3) 7.49 (3H, m), 3.85 (3H, s), 3.58
(3H, s), 2.72 (3H, s), 2.54 (3H, s) and the title compound
(83%) sufficiently pure for use in the next step, mp 183–186 ЊC
(dec.); δH (60 MHz; (CD3)2SO–CDCl3) 7.15 (1H, d, J 9.0), 7.69
(1H, d, J 9.0), 3.87 (3H, s), 3.79 (3H, s), 2.67 (3H, s), 2.28
(3H, s).
3-Benzoyl-5-methoxy-1,2-dimethyl-4-nitroindole 11b. N-
Methyl derivative (89%) as an off-white solid after column
chromatography (dichloromethane); δH (60 MHz; CDCl3) 6.84–
7.70 (8H, m), 3.66 (6H, s), 2.47 (3H, s); which was used in the
next step without further purification, and the title compound
(75%), mp 180–184 ЊC; δH (60 MHz; (CD3)2SO–CDCl3) 7.72
(1H, d, J 9.0), 7.51 (5H, m), 7.14 (1H, d, J 9.0), 3.88 (3H, s),
3.76 (3H, s), 2.21 (3H, s).
5-Methoxy-1,2-dimethyl-4-nitro-3-(2-thienylcarbonyl)indole
11c. N-Methyl derivative (76%) as an off-white solid after
column chromatography (ethyl acetate–hexane, 1 : 1), mp 106–
107 ЊC; δH (60 MHz; CDCl3) 6.74–7.64 (6H, m), 3.73 (3H, s),
3.66 (3H, s), 2.53 (3H, s); which was used in the next step with-
out further purification, and the title compound (43%), purified
by column chromatography (ethyl acetate–hexane, 1 : 1), mp
183–184 ЊC; δH (60 MHz; (CD3)2SO–CDCl3) 7.81 (1H, d, J 9.0),
7.1–7.91 (3H, m), 7.07 (1H, d, J 9.0), 3.88 (3H, s), 3.75 (3H, s),
2.39 (3H, s).
General method for the preparation of 3-acylindoles 10
5-Methoxy-2-methylindole (3.2 g, 20 mmol) was dissolved in
diethyl ether (anhydrous, 15 cm3) and added drop-wise, with
vigorous stirring, to a solution of ethylmagnesium bromide
(3.0 mol dmϪ3, 6.8 cm3, 20 mmol) in diethyl ether (anhydrous,
10 cm3) under a dry nitrogen atmosphere. The solution was
heated under reflux for 0.5 h, cooled to 0 ЊC and the appropriate
acyl chloride (20 mmol in ether (10 cm3)) added with vigorous
stirring. The solution was heated under reflux for a further 1 h,
cooled and saturated ammonium chloride (100 cm3) added. The
solution was extracted with ethyl acetate (500 cm3) and washed
with saturated sodium bicarbonate solution (150 cm3) and brine
(150 cm3) then evaporated by 50% and the resulting precipitate
collected and washed with ether to give a white solid which was
used without further purification.
General method for the preparation of 3-acylindolequinones 12
The nitro compound 11 (1.91 mmol) was dissolved in ethanol
(75 cm3) and tin (powder, 2.2 g, 18.5 mmol) added, followed by
hydrochloric acid (3.0 mol dmϪ3, 30 cm3). The solution was
stirred for 0.5 h at 20 ЊC, decanted and ethyl acetate (250 cm3)
added. The organic solution was then washed with saturated
sodium bicarbonate solution (2 × 100 cm3) and brine (sat., 50
cm3), dried and evaporated. The residue was dissolved in acet-
one (60 cm3) and Fremy’s salt (0.25 g in 60 cm3 Na2HPO4–
NaH2PO4 buffer (0.3 mol dmϪ3, pH 6.0)) added. The solution
was stirred at 20 ЊC for 0.3 h and the acetone removed in vacuo.
The resulting precipitate was collected by suction filtration,
3-Acetyl-2-methyl-5-methoxyindole 10a. (62%), mp 219–
224 ЊC; δH (60 MHz; (CD3)2SO–CDCl3) 7.57 (3H, m), 3.82 (3H,
s), 2.72 (3H, s), 2.54 (3H, s).
856
J. Chem. Soc., Perkin Trans. 2, 2001, 843–860

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washed with water and dried in vacuo for 12 h to give the
title compound as an orange solid.
column chromatography (90% dichloromethane–10% ethyl
acetate) to yield the title compound (0.017 g, 25%) as a orange
solid, mp 237–239 ЊC (from dichloromethane–light petroleum)
(Found: C, 60.9; H, 4.0; N, 7.5. C19H16N2O6ؒ0.3H2O requires C,
61.0; H, 4.5; N, 7.5%); λmax (MeOH)/nm 450 (log ε 2.74), 290
(3.85), 226 (3.83); νmax (KBr disc)/cmϪ1 3119, 2970, 2919, 1670,
1644, 1593; δH (300 MHz; CDCl3) 8.18, 7.02 (4H, m), 5.64 (1H,
s), 5.39 (2H, s), 4.23 (2H, m), 3.83 (3H, s), 2.87 (2H, m), 2.57
(2H, m); δC (100 MHz; CDCl3) 178.0, 177.8, 163.5, 160.5, 143.6,
141.7, 126.6, 125.9, 124.0, 114.7, 111.6, 105.8, 62.8, 56.6, 47.0,
27.3, 23.5; m/z (EI, relative intensity) 368 (M+, 1%), 231 (9), 230
(67), 44 (100).
3-Acetyl-5-methoxy-1,2-dimethylindole-4,7-dione 12a. (64%),
mp 227–228 ЊC; δH (60 MHz; CDCl3) 5.64 (1H, s), 3.89 (3H, s),
3.84 (3H, s), 2.62 (3H, s), 2.36 (3H, s).
3-Benzoyl-5-methoxy-1,2-dimethylindole-4,7-dione
12b.
(71%), mp 178–180 ЊC; δH (60 MHz; CDCl3) 7.23–7.88 (5H, m),
5.62 (1H, s), 3.94 (3H, s), 3.72 (3H, s), 2.29 (3H, s).
5-Methoxy-1,2-dimethyl-3-(2-thienylcarbonyl)indole-4,7-dione
12c. (78%), mp 194–196 ЊC; δH (60 MHz; CDCl3) 6.94–7.66
(3H, m), 5.63 (1H, s), 3.94 (3H, s), 3.75 (3H, s), 2.29 (3H, s).
General method for the Mitsunobu reaction
The 3-hydroxymethylindolequinone (1.96 mmol), triphenyl-
phosphine (3.8 mmol), diethyl azodicarboxylate (3.9 mmol) and
4-nitrophenol (3.3 mmol) were stirred overnight in tetrahydro-
furan at 50 ЊC. Excess solvent was removed and the majority of
the product triturated out with ether, and filtered off. The resi-
due was dissolved in dichloromethane washed with water, dried
(Na2SO4) and concentrated. The crude residue was purified by
column chromatography (light petroleum–ethyl acetate 1 : 1) to
yield the title compound as an orange crystalline solid. The
following compounds were thus prepared.
General method for the preparation of hydroxymethyl derivatives
28, 30, 31
Compound 12 (1 mmol) was dissolved in methanol (anhydrous,
N2-degassed, 100 cm3) and sodium borohydride (0.5 g, 26.5
mmol) added with stirring. After 10 min water (50 cm3) was
added followed by ethyl acetate (50 cm3) and the solution
shaken vigorously. The solution was then extracted with ethyl
acetate (4 × 100 cm3) and washed with saturated sodium
bicarbonate solution (100 cm3) and brine (100 cm3), dried and
evaporated. The residue was purified by column chromato-
graphy (ethyl acetate–hexane, 2 : 1) to give the title compound as
an orange solid, recrystallised from ethyl acetate–hexane.
5-Methoxy-1-methyl-3-(4-nitrophenoxy)methylindole-4,7-
dione 32. (67%) as an orange crystalline solid; mp 207–209 ЊC;
λmax (MeOH)/nm 284 (log ε 1.02), 224 (0.99); νmax (Nujol)/cmϪ1
3058, 1675, 1644, 1588, 1516, 1342, 1184; δH (300 MHz; CDCl3)
8.21 (2H, d, J 9.3, ArH), 7.04 (2H, d, J 9.3), 6.88 (1H, s), 5.71
(1H, s), 5.38 (2H, s), 3.97 (3H, s), 3.84 (3H, s); δC (75 MHz;
CDCl3) 178.9, 177.7, 163.4, 160.3, 141.8, 130.0, 128.5, 125.9,
121.0, 119.9, 114.8, 107.0, 63.1, 56.6, 36.4; m/z (EI, relative
intensity) 342 (M+, 3%), 205 (38), 204 (100), 174 (8), 161 (14),
139 (24); m/z (HRMS) 342.0853 (C17H14N2O6 requires M
342.0851).
3-(1-Hydroxyethyl)-5-methoxy-1,2-dimethylindole-4,7-dione
28. (56%), mp 148–150 ЊC (Found: C, 62.8; H, 6.0; N, 5.6.
C13H15NO4 requires C, 62.6; H, 6.1; N, 5.6%); δH (60 MHz;
CDCl3) 5.58 (1H, s), 4.80 (1H, m), 3.86 (3H, s), 3.79 (3H, s),
2.17 (3H, s), 1.45 (3H, d, J 4.8) (OH not observed); m/z (EI,
relative intensity) 248.9 (M+, 22%), 234.0 (100), 215.9 (8), 205.8
(22).
3-(1-Hydroxy-1-phenylmethyl)-5-methoxy-1,2-dimethyl-
indole-4,7-dione 30. (38%), mp 138–140 ЊC (Found: C, 67.3; H,
5.8; N, 4.0. C18H17NO4ؒ0.5 H2O requires C, 67.5; H, 5.7; N,
4.4%); δH (60 MHz; CDCl3) 7.28 (5H, m), 5.78 (1H, br), 5.58
(1H, s), 3.89 (3H, s), 3.77 (3H, s), 2.28 (3H, s); m/z (EI, relative
intensity) 310.8 (M+, 100%), 294.7 (54), 217.8 (39), 205.8 (67).
5-Methoxy-1,2-dimethyl-3-(4-nitrophenoxymethyl)indole-4,7-
dione 34. Prepared as previously described39 in 57% yield.
5-Methoxy-1,2,6-trimethyl-3-(4-nitrophenoxymethylindole-
4,7-dione 35. (72%), mp 193–195 ЊC (Found: C, 60.6; H, 4.8; N,
7.2. C19H18N2O6ؒ0.3 H2O requires C, 60.7; H, 5.0; N, 7.4%); λmax
(MeOH)/nm 458 (log ε 2.21), 318 (3.24), 290 (3.43); νmax
(CH2Cl2)/cmϪ1 1665, 1642, 1592; δH (300 MHz; CDCl3) 8.18
(2H, d, J 9.2), 7.05 (2H, d, J 9.2), 5.37 (2H, s) 3.98 (3H, s), 3.89
(3H, s), 2.30 (3H, s), 1.96 (3H, s); δC (100 MHz; CDCl3) 180.0,
179.1, 163.6, 156.1, 141.6, 138.2, 129.2, 128.8, 125.9, 121.6,
115.4, 114.9, 61.2, 61.1, 32.5, 9.9, 8.8; m/z (EI, relative intensity)
232 (100%), 127 (40), 57 (77); m/z (HRMS) 370.1162
(C19H18N2O6 requires M 370.1165).
3-[1-Hydroxy-1-(2-thienyl)methyl]-5-methoxy-1,2-dimethyl-
indole-4,7-dione 31. (46%), mp 175–176 ЊC (Found: C, 58.8; H,
4.8; N, 4.1. C16H15NO4Sؒ0.5 H2O requires C, 58.8; H, 4.9; N,
4.3%); δH (60 MHz; CDCl3) 7.17 (1H, m), 6.84 (2H, m), 5.93
(1H, br), 5.88 (1H, d, J 4.8), 5.59 (1H, s), 3.90 (3H, s), 3.78 (3H,
s), 2.27 (3H, s); m/z (EI, relative intensity) 317 (M+, 100%), 301
(76), 286 (25), 233 (58), 218 (30), 206 (39).
Preparation of 3-(4-nitrophenoxy)alkyl indolequinones: 7-
methoxy-9-[(4-nitrophenoxy)methyl]-2,3-dihydro-1H-pyrrolo-
[1,2-a]indole-5,8-dione 33
5-Methoxy-1-methyl-3-[(4-nitrophenoxy)methyl]-2-phenyl-
indole-4,7-dione 37. (84%) as an orange–yellow solid, mp 229–
230 ЊC (Found: C, 65.1; H, 4.2; N, 6.5. C23H18N2O6ؒ0.3 H2O
requires C, 65.2; H, 4.4; N, 6.6%); λmax (MeOH)/nm 444 (log
ε 3.10), 284 (4.06); νmax (KBr disc)/cmϪ1 3114, 3068, 3017, 2965,
2934, 1665, 1639, 1598; δH (300 MHz; CDCl3) 8.14 (2H, d,
J 9.2), 7.49 (3H, m), 7.35 (2H, m), 6.92 (2H, d, J 9.2), 5.74 (1H,
s), 5.16 (2H, s), 3.85 (3H, s), 3.83 (3H, s); δC (CDCl3) 179.1,
177.8, 163.7, 160.0, 142.1, 141.6, 130.4, 129.8, 129.7, 128.9,
128.2, 125.8, 121.6, 116.6, 114.9, 107.0, 61.4, 56.6, 34.1; m/z (EI,
relative intensity) 418 (M+, 6%), 388 (13), 311 (89), 296 (100);
m/z (HRMS) 419.1243 (C23H19N2O6 requires MH 419.1243).
To a stirred solution of the hydroxymethylindolequinone 14
(0.046 g, 0.18 mmol) in dichloromethane (10 cm3) was added
thionyl chloride (1.6 g, 13.4 mmol). The mixture was stirred at
room temperature overnight. The solvent was removed in
vacuo. The chloride was used directly in the next step without
purification. 4-Nitrophenol (0.054 g, 0.39 mmol) in dimethyl-
formamide (5 cm3) was added to a stirring suspension of
sodium hydride (0.009 g, 0.37 mmol) in dimethylformamide
(10 cm3) at 0 ЊC. The mixture was stirred at room temperature
for 45 min. A solution of the chloride in dimethylformamide
(5 cm3) was added dropwise at 0 ЊC and the mixture stirred at
room temperature for 2 h. Saturated ammonium chloride solu-
tion was added and the mixture extracted with ethyl acetate.
The ethyl acetate layer was washed twice with water, dried
(MgSO4) and concentrated. The crude material was purified by
2-(Biphenyl-4-yl)-5-methoxy-3-[(4-nitrophenoxy)methyl]-1-
methylindole-4,7-dione 38. (89%) as an orange–red solid, mp
128–129 ЊC (Found: C, 68.8; H, 4.5; N, 5.4. C29H22N2O6ؒ0.6
H2O requires C, 68.9; H, 4.6; N, 5.5%); λmax (MeOH)/nm 496
J. Chem. Soc., Perkin Trans. 2, 2001, 843–860
857

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(log ε 3.19) and 280 (4.56); νmax (KBr disc)/cmϪ1 3083, 3027,
2925, 1742, 1680, 1644, 1598; δH (300 MHz; CDCl3) 8.16 (2H,
d, J 9.2), 7.71 (2H, m), 7.62 (2H, m), 7.51–7.40 (5H, m), 6.96
(2H, d, J 9.2), 5.75 (1H, s), 5.21 (2H, s), 3.90 (3H, s), 3.85 (3H,
s); δC (100 MHz; CDCl3) 179.0, 177.8, 163.7, 160.0, 142.5,
141.8, 141.6, 139.8, 130.8, 129.9, 129.0, 128.0, 127.5, 127.1,
127.0, 125.8, 121.7, 116.8, 114.9, 107.0, 61.4, 56.6, 34.2; m/z (CI,
relative intensity) 495 (MH+, 2%), 373 (M Ϫ NO2C6H4OH,
100), 357 (25), 298 (10), 138 (90).
114.9, 61.3, 61.1, 10.4, 8.7; m/z (EI, relative intensity) 432 (M+,
4%), 295 (100), 251 (33), 118 (30), 77 (36); m/z (HRMS)
432.1327 (C24H20N2O6 requires M 432.1321).
1-(4-Fluorophenyl)-5-methoxy-2-methyl-3-[(4-nitrophenoxy)-
methyl]indole-4,7-dione 44. (78%), mp 239–241 ЊC; λmax
(MeOH)/nm 446 (log ε 3.25), 288 (4.42); νmax (CH2Cl2)/cmϪ1
1675, 1634, 1592; δH (400 MHz; CDCl3) 8.21 (2H, d, J 9.2),
7.26–7.17 (4H, m), 7.09 (2H, d, J 9.2), 5.57 (1H, s), 5.43 (2H, s),
3.81 (3H, s), 2.10 (3H, s); δC (100 MHz; CDCl3) 178.5, 177.0,
163.6, 162.8 (d, JCF 249.9), 159.5, 141.7, 138.8, 132.3, 129.0 (d,
JCF 9.0), 126.0, 121.7, 116.5, (d, JCF 23.2), 115.7, 114.9, 106.8,
61.2, 56.6, 10.4; m/z (EI, relative intensity) 185 (8%), 155 (25),
127 (29), 69 (45), 57 (100).
5-Methoxy-1-methyl-2-(2-naphthyl)-3-[(4-nitrophenoxy)-
methyl]indole-4,7-dione 39. (77%) as an orange solid, mp 165–
167 ЊC (Found: C, 66.9; H, 4.2; N, 6.0. C27H20N2O6ؒ0.9 H2O
requires C, 66.9; H, 4.5; N, 5.8%); λmax (MeOH)/nm 460 (log
ε 3.31), 286 (4.58), 266 (4.59); νmax (KBr disc)/cmϪ1 2952, 1677,
1642, 1591; δH (300 MHz, CDCl3) 8.14 (2H, d, J 9.2), 7.89 (2H,
m), 7.83 (2H, m), 7.59 (2H, m), 7.42 (1H, dd, J 8.4, J 1.7), 6.91
(2H, d, J 9.2), 5.76 (1H, s), 5.21 (2H, s), 3.88 (3H, s), 3.86 (3H,
s); δC (75 MHz; CDCl3) 179.1, 177.9, 163.7, 160.0, 142.2, 141.5,
133.4, 132.9, 130.5, 129.8, 128.7, 128.2, 127.9, 127.5, 127.1,
126.9, 125.8, 125.4, 121.7, 116.9, 114.9, 107.1, 61.4, 56.6, 34.3,
10.7; m/z (EI, relative intensity) 331 (MH2+ Ϫ HOC6H4NO2,
29%), 330 (MH+ϪHOC6H4NO2, 100), 139 (HOC6H4NO2, 52),
109 (63), 65 (72).
5-Methoxy-2-methyl-3-(4-nitrophenoxymethyl)-1-propyl-
indole-4,7-dione 45. (64%), mp > 250 ЊC (Found: C, 62.1; H,
5.2; N, 7.1. C20H20N2O6 requires C, 62.5; H, 5.2; N, 7.3%); λmax
(MeOH)/nm 456 (log ε 3.21), 316 (4.10), 292 (4.39); νmax (KBr
disc)/cmϪ1 3063, 2965, 2940, 1676, 1637, 1592; δH (300 MHz;
CDCl3) 8.18 (2H, d, J 9.2), 7.05 (2H, d, J 9.2), 5.63 (1H, s), 5.39
(2H, s), 4.27 (2H, m), 3.81 (3H, s), 2.32 (3H, s), 1.73 (2H, sextet,
J 7.5), 0.96 (3H, t, J 7.5); δC (100 MHz; CDCl3) 178.34, 178.27,
163.6, 159.5, 141.6, 137.5, 128.6, 125.9, 121.4. 115.8, 114.9,
106.9, 61.2, 56.5, 46.9, 23.7, 11.0, 9.8; m/z (CI, relative intensity)
+
1-Cyclopropyl-5-methoxy-2-methyl-3-[(4-nitrophenoxy)-
methyl]indole-4,7-dione 40. (80%), mp 217–219 ЊC (Found: C,
61.1; H, 4.5; N, 6.9. C20H18N2O6ؒ0.6 H2O requires C, 61.1; H,
4.9; N, 7.1%); λmax (MeOH)/nm 450 (log ε 3.04) 318 (3.90), 294
(4.21); νmax (CH2Cl2)/cmϪ1 1674, 1641, 1592; δH (400 MHz;
CDCl3) 8.17 (2H, d, J 9.2), 7.03 (2H, d, J 9.2), 5.64 (1H, s), 5.36
(2H, s), 3.78 (3H, s), 3.23–3.15 (1H, m), 2.42 (3H, s), 1.33–1.21
(2H, m), 0.97–0.86 (2H, m); δC (100 MHz; CDCl3) 178.5, 177.1,
163.7, 159.0, 141.6, 140.3, 130.5, 125.9, 121.7, 115.3, 114.9,
107.2, 61.0, 56.4, 28.1, 11.6, 10.0 (2 × CH2); m/z (EI, relative
intensity) 244 (100%), 139 (15), 65 (26); m/z (HRMS) 382.1163
(C20H18N2O6 requires M 382.1165).
402 (M + NH4 , 10%), 385 (M+, 5), 263 (55), 248 (100).
5-Methoxy-2,6-dimethyl-3-[(4-nitrophenoxy)methyl]-1-
propylindole-4,7-dione 46. (64%) as an orange crystalline solid,
mp 120–122 ЊC (Found: C, 62.9; H, 5.5; N, 6.8. C21H22N2O6ؒ0.1
H2O requires C, 63.0; H, 5.6; N, 7.0%); λmax (MeOH)/nm 452
(log ε 2.96), 288 (4.25); νmax (KBr disc)/cmϪ1 2966, 2930, 1657,
1637, 1606, 1591; δH (400 MHz; CDCl3) 8.20 (2H, d, J 9.2), 7.07
(2H, d, J 9.2), 5.37 (2H, s), 4.25 (2H, m), 3.98 (3H, s), 2.31 (3H,
s), 1.97 (3H, s), 1.74 (2H, sextet, J 7.5), 0.98 (3H, t, J 7.3);
δC (100 MHz; CDCl3) 180.1, 178.6, 163.7, 156.0, 141.6, 137.8,
129.2, 128.4, 125.9, 121.8, 115.5, 114.9, 61.2, 61.0, 47.0, 23.7,
11.1, 9.8, 8.8; m/z (EI, relative intensity) 398 (M+, 3%), 260
(M+ Ϫ HOC6H4NO2, 100), 218 (37); m/z (HRMS) 398.1471
(C21H22N2O6 requires 398.1478).
1-Benzyl-2-ethyl-5-methoxy-3-[(4-nitrophenoxy)methyl]-
indole-4,7-dione 41. (76%), mp 177–179 ЊC; λmax (MeOH)/nm
454 (log ε 2.08), 316 (2.96), 290 (3.22); νmax (CH2Cl2)/cmϪ1 1665,
1638, 1597; δH (300 MHz; CDCl3) 8.19 (2H, d, J 9.2), 7.33–7.26
(3H, m), 7.06 (2H, d, J 9.2), 7.08–6.99 (2H, m), 5.67 (2H, s),
5.65 (1H, s), 5.41 (2H, s), 3.81 (3H, s), 2.67 (2H, q, J 7.5), 1.07
(3H, t, J 7.5); δC (100 MHz; CDCl3) 178.4, 178.0, 163.6, 159.5,
144.0, 141.6, 136.3, 128.9, 128.7, 127.7, 126.0 (2 × CH), 126.0
(2 × CH), 121.8, 115.8, 114.9, 107.1, 61.0, 56.6, 48.4, 17.5, 14.2;
m/z (EI, relative intensity) 308 (M+ Ϫ HOC6H4NO2, 26%), 91
(100).
5-Methoxy-1,2-dimethyl-3-[1-(4-nitrophenoxy)ethyl]indole-
4,7-dione 47. (82%) as an orange–yellow solid, mp 178–179 ЊC
(Found: C, 61.7; H, 5.0; N, 7.5. C19H18N2O6 requires C, 61.6; H,
4.9; N, 7.6%); λmax (MeOH)/nm 458 (log ε 3.17), 290 (4.37), 236
(4.04); νmax (KBr disc)/cmϪ1 2976, 2925, 1665, 1634, 1593;
δH (400 MHz, CDCl3) 8.09 (2H, d, J 9.2), 6.91 (2H, d, J 9.2),
6.35 (1H, q, J 6.5), 5.64 (1H, s), 3.84 (3H, s), 3.81 (3H, s), 2.28
(3H, s), 1.66 (3H, d, J 6.5); δC (100 MHz; CDCl3) 178.6, 178.4,
162.8, 159.5, 141.4, 135.2, 128.6, 125.8, 122.3, 120.0, 115.2,
106.9, 69.4, 56.5, 32.1, 22.0, 10.5; m/z (EI, relative intensity) 232
(M+ Ϫ NO2C6H4OH, 100%), 206 (10), 127 (8), 110 (48).
5-Methoxy-2-methyl-3-[(4-nitrophenoxy)methyl]-1-phenyl-
indole-4,7-dione 42. (80%), mp 249–251 ЊC; λmax (MeOH)/nm
444 (log ε 2.87), 288 (4.06); νmax (CH2Cl2)/cmϪ1 1676, 1643,
1590; δH (400 MHz; CDCl3) 8.21 (2H, d, J 8.8) 7.54–7.52 (3H,
m), 7.26–7.24 (2H, m), 7.10 (2H, d, J 8.8), 5.57 (1H, s), 5.44
(2H, s), 3.81 (3H, s), 2.10 (3H, s); δC (100 MHz; CDCl3) 178.6,
177.0, 163.7, 159.5, 141.6, 138.8, 136.7, 130.0, 129.5, 127.1,
126.0, 121.7, 115.6, 114.9, 106.8, 61.2, 56.6, 10.5 (one C not
observed); m/z (EI, relative intensity) 418 (M+, 0.2%), 280 (58),
81 (85), 55 (100); m/z (HRMS) 418.1160 (C23H18N2O6 requires
M 418.1165).
5-Methoxy-1,2-dimethyl-3-[1-(4-nitrophenoxy)-1-phenyl-
methyl]indole-4,7-dione 49. (80%) as an orange solid, mp 208–
209 ЊC (Found: C, 66.4; H, 4.5; N, 6.3. C24H20N2O6 requires C,
66.7; H, 4.7; N, 6.5%); λmax (MeOH)/nm 456 (log ε 3.22), 290
(4.40); νmax (KBr disc)/cmϪ1 2926, 2851, 1666, 1658, 1631, 1599;
δH (300 MHz; CDCl3) 8.15 (2H, d, J 9.2), 7.49–7.44 (3H, m),
7.38–7.28 (3H, m), 7.29 (2H, d, J 9.2), 5.67 (1H, s), 3.86 (3H, s),
3.82 (3H, s), 2.20 (3H, s); δC (100 MHz; CDCl3) 178.8, 178.4,
162.6, 159.6, 141.8, 139.5, 136.3, 128.7, 128.6, 127.9, 126.0,
125.9, 120.7, 120.5, 115.5, 107.0, 73.5, 56.6, 32.2, 10.7; m/z (EI,
relative intensity) 295 (MH+ Ϫ HOC6H4NO2, 13%), 294
(MH+ Ϫ HOC6H4NO2, 40), 139 (HOC6H4NO2, 20), 69 (100).
5-Methoxy-2,6-dimethyl-3-[(4-nitrophenoxy)methyl]-1-
phenylindole-4,7-dione 43. (70%), mp 134–136 ЊC; λmax
(MeOH)/nm 452 (log ε 2.40), 322 (3.51), 294 (3.63); νmax
(CH2Cl2)/cmϪ1 1662, 1649, 1593; δH (400 MHz; CDCl3) 8.22
(2H, d, J 9.2), 7.54–7.52 (3H, m), 7.26–7.23 (2H, m), 7.09 (2H,
d, J 9.2), 5.42 (2H, s), 3.99 (3H, s), 2.09 (3H, s), 1.88 (3H, s);
δC (100 MHz; CDCl3) 180.3, 177.6, 163.7, 156.1, 141.7, 139.0,
136.9, 129.8, 128.5, 129.4, 129.0, 127.1, 126.0, 122.0, 115.4,
5-Methoxy-1,2-dimethyl-3-[1-(4-nitrophenoxy)-1-(2-thienyl)-
methyl]-indole-4,7-dione 50. (49%) as an orange solid, mp 178–
180 ЊC (from ethyl acetate) (Found: C, 60.3; H, 4.1; N, 6.4.
C22H18N2O6S requires C, 60.3; H, 4.1; N, 6.4%); δH (60 MHz;
858
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CDCl3) 8.12 (2H, m), 7.57 (1H, br d), 6.90–7.3 (4H, m), 6.96
(1H, s), 5.65 (1H, s), 3.84 (3H, s), 3.83 (3H, s), 2.3 (3H, s).
tetrahydrofuran (15 cm3) was added silver() oxide (0.075 g, 0.32
mmol) and propan-2-ol (0.5 cm3, 6.5 mmol). The reaction mix-
ture was stirred overnight at room temperature. The mixture
was filtered through a pad of Celite. The filtrate was concen-
trated and purified by column chromatography (95% dichloro-
methane–5% ethyl acetate) to yield the title compound as an
orange crystalline solid (0.02 g, 91%), mp 158–159 ЊC (from
ether–petroleum ether) (Found: C, 72.9; H, 5.7; N, 3.2.
C26H25NO4ؒ0.8 H2O requires C, 72.6; H, 6.2; N, 3.2%); λmax
(MeOH)/nm 450 (log ε 3.27), 346 (3.51), 278 (4.57); νmax (KBr
disc)/cmϪ1 2971, 2930, 2848, 1670, 1644, 1598; δH (300 MHz;
CDCl3) 7.72 (2H, d, J 8.0), 7.65 (2H, d, J 7.1), 7.55–7.37 (5H,
m), 5.70 (1H, s), 4.48 (2H, s), 3.87 (3H, s), 3.84 (3H, s), 3.75
(1H, septet, J 6.1), 1.20 (6H, d, J 6.1); δC (100 MHz; CDCl3)
179.2, 177.7, 160.1, 141.9, 141.6, 140.2, 130.9, 129.9, 128.9,
127.8, 127.6, 127.2, 127.1, 120.3, 106.9, 71.5, 60.0, 56.5, 34.2,
22.2; m/z (EI, relative intensity) 415 (M+, 14%), 373 (32), 372
(88), 356 (23), 91 (100); m/z (HRMS) 415.1784 (C26H25NO4
requires M 415.1783).
1,2-Dimethyl-5-(morpholin-1-yl)-3-(4-nitrophenoxy)methyl-
indole-4,7-dione 36. Morpholine (1.00 g, 11 mmol) was added
to a stirring solution of 5-methoxy-1,2-dimethyl-3-(4-nitro-
phenoxy)methylindole-4,7-dione 34 (11 mg, 30 µmol) in
acetonitrile (5 cm3). The reaction mixture was stirred at room
temperature for 5 days. Water (10 cm3) was added, the mixture
was extracted with dichloromethane (3 × 15 cm3), washed with
water (2 × 10 cm3), brine (2 × 10 cm3), dried (Na2SO4) and
evaporated under reduced pressure. The crude product was pre-
absorbed onto silica and purified by flash column chromoto-
graphy, eluting with ethyl acetate–light petroleum (1 : 1) to give
the title compound (9 mg, 73%) as a purple crystalline solid; mp
266–267 ЊC (Found: C, 60.8; H, 5.1; N, 10.1. C21H21N3O6ؒ0.2
H2O requires C, 60.8; H, 5.1; N, 10.1%); λmax (MeOH)/nm 520
(log ε 4.03), 314 (3.97); νmax (CH2Cl2)/cmϪ1 3053, 2986, 1654,
1629, 1588, 1521, 1480, 1454, 1352, 1260, 1219; δH (200 MHz;
CDCl3) 8.20 (2H, d, J 9.3), 7.05 (2H, d, J 9.3), 5.50 (1H, s), 5.34
(2H, s), 3.91 (3H, s), 3.83 (4H, m), 3.40 (4H, m), 2.29 (3H, s),
and 1.25 (2H, s); δC (100 MHz; CDCl3) 180.9, 178.3, 163.8,
153.4, 141.6, 137.2, 129.3, 125.9 (2 × CH), 122.0, 115.3, 114.8,
110.4, 66.4, 61.3, 49.8, 32.2, 9.7; m/z (EI, relative intensity) 411
(M+, 5%), 273 (100), 243 (24), 215 (18), 188 (18), 139 (30); m/z
(HRMS) 411.1426 (C21H21N3O6 requires M 411.1430).
Acknowledgements
This work is supported by the Cancer Research Campaign
(CRC) and the Gray Laboratory Cancer Research Trust
(GLCRT). We are also grateful to the EU for a fellowship to
P. B., the University of Exeter for a studentship to A. R. H.,
Maybridge Chemical Company for a gift of starting materials,
and the EPSRC Mass Spectrometry Service at Swansea for
mass spectra.
3-(1-Hydroxyethyl)-1,2-dimethyl-5-(4-methylpiperazin-1-yl)-
indole-4,7-dione 29. Compound 28 (100 mg, 0.4 mmol) was
dissolved in DMF (3 cm3) and N-methylpiperazine (0.75 g, 7.5
mmol) added. The solution was stirred for 24 h and ethyl acet-
ate (50 cm3) added, followed by saturated NaHCO3 (50 cm3).
The ethyl acetate layer was separated and the aqueous phase
further extracted with ethyl acetate (50 cm3) and the combined
extracts washed with water (50 cm3) and brine (50 cm3), dried
and evaporated. The residue was purified on silica, eluting with
ethyl acetate–methanol (1 : 1) to give a red solid (50 mg, 39%);
mp 147–149 ЊC (from ethyl acetate) (Found: C, 63.4; H, 7.3; N,
12.9. C17H23N3O3ؒ0.3 H2O requires C, 63.2; H, 7.3; N, 13.0%);
δH (60 MHz; CDCl3) 5.49 (1H, s), 4.85 (1H, q, J 6.5), 3.85 (3H,
s), 3.47 (4H, m), 2.66 (4H, m), 2.32 (3H, s), 2.18 (3H, s), 1.53
(3H, d, J 6.5).
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