Potent enantioselective inhibition of DNA-dependent protein kinase (DNA-PK) by atropisomeric chromenone derivatives

Article abstract of DOI:10.1039/c2ob26035b

Substitution at the 7-position of the chromen-4-one pharmacophore of 8-(dibenzo[b,d]thiophen-4-yl)-2-morpholino-4H-chromen-4-one NU7441, a potent and selective DNA-dependent protein kinase (DNA-PK) inhibitor, with allyl, n-propyl or methyl enabled the resolution by chiral HPLC of atropisomers. Biological evaluation against DNA-PK of each pair of atropisomers showed a marked difference in potency, with biological activity residing exclusively in the laevorotatory enantiomer.

Full text of DOI:10.1039/c2ob26035b

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PAPER
Potent enantioselective inhibition of DNA-dependent protein kinase
(DNA-PK) by atropisomeric chromenone derivatives†
Kate M. Clapham,‡a Tommy Rennison,‡a Gavin Jones,a Faye Craven,a Julia Bardos,b Bernard T. Golding,a
Roger J. Griffin,a Karen Haggerty,a Ian R. Hardcastle,a Pia Thommes,c Attilla Tingc and Céline Cano*a
Received 29th May 2012, Accepted 12th July 2012
DOI: 10.1039/c2ob26035b
Substitution at the 7-position of the chromen-4-one pharmacophore of 8-(dibenzo[b,d]thiophen-4-yl)-
2-morpholino-4H-chromen-4-one NU7441, a potent and selective DNA-dependent protein kinase
(DNA-PK) inhibitor, with allyl, n-propyl or methyl enabled the resolution by chiral HPLC of
atropisomers. Biological evaluation against DNA-PK of each pair of atropisomers showed a marked
difference in potency, with biological activity residing exclusively in the laevorotatory enantiomer.
of a dibenzothiophen-4-yl substituent at the 8-position of 2-mor-
pholino-4H-chromen-4-one conferred excellent inhibitory
Introduction
Arguably, the most cytotoxic of all DNA lesions are DNA
activity against DNA-PK, as exemplified by NU7441 (1, IC50
=
28 nM).19 With a view to optimising the biological and pharma-
ceutical properties of 1, both the core chromenone scaffold and
the dibenzothiophen-4-yl moiety have been systematically
modified. Importantly, our interest in substituted dibenzothio-
phenes arose from the preparation of the highly potent DNA-PK
inhibitor KU-0060648 (2; IC50 = 5 nM).20 More recently, alkyl-
ation at the 3-position of the dibenzothiophen-4-yl group of 1
has provided valuable SAR information that has enabled further
refinement of the homology model (Fig. 1).21 Thus, two possible
poses were identified for the interaction of 1 with the ATP-
binding domain of DNA-PK: conformation (a) positions the
chromenone and dibenzothiophene rings in an orthogonal
relationship, with the alternative ‘in plane’ pose (b) being
energetically less favorable.
The introduction of an allyl (3), n-propyl (4) or methyl (5)
substituent at the dibenzothiophene 3-position generated stable
pairs of atropisomers due to restricted rotation between the
chromen-4-one and dibenzothiophene rings. Interestingly, the
differential DNA-PK inhibitory activity between the two atrop-
isomers gave an indication of the interaction of this class of
inhibitors within the ATP-binding domain of DNA-PK, albeit
with a loss of potency compared with the parent compound 1.
Thus, the homology model predicts that atropisomer 5 may only
adopt the energetically preferred orthogonal conformation
[Fig. 1, (c)], with the methyl substituent being accommodated
within a narrow hydrophobic pocket in the ATP-binding pocket.
During the past decade, increasing interest has been given to
enantioselective binding of chiral drugs with their biological
targets and the implication for both pharmacological activity
and toxicity.22–29 In light of this, we decided to explore further
the configuration of the biphenyl junction between the
double-strand breaks (DSBs), the principal cytotoxic lesions pro-
duced by IR and radiomimetic chemicals, and which are also
generated when the DNA replication apparatus encounters other
DNA lesions, such as DNA single-strand breaks (SSBs). It is
now well established that the two major mechanisms involved in
DSB repair are largely distinct and complementary pathways,
namely homologous recombination (HR) and non-homologous
end-joining (NHEJ).1,2 DNA-dependent protein kinase (DNA-
PK), a member of the phosphatidylinositol (PIa) 3-kinase related
kinase (PIKK) family, is a multi-component serine/threonine
protein kinase that plays a key role in NHEJ of the repair of
mammalian DNA DSBs.3,4 Interestingly, human cell lines with
defects in DNA-PK function are hypersensitive to agents that
elicit DNA DSBs.5,6 Therefore, by impeding DNA DSB repair,
selective DNA-PK inhibitors have potential application as radio-
and chemo-potentiators in the treatment of cancer.7–11
Using a homology model of the ATP-binding site of
DNA-PK, derived from the crystal structure of PI3Kγ,12 we have
identified potent DNA-PK inhibitors with defined structure–
activity relationships (SARs).13–18 Notably, the incorporation
aNewcastle Cancer Centre, Northern Institute for Cancer Research,
School of Chemistry, Bedson Building, Newcastle University,
Newcastle upon Tyne, NE1 7RU, UK. E-mail: celine.cano@ncl.ac.uk;
Tel: +44 (0) 1912227060
bKuDOS Pharmaceuticals, Ltd, 410 Cambridge Science Park, Milton
Road, Cambridge CB4 0PE, UK
cAstraZeneca Oncology iMed, Mereside, Alderley Park, Macclesfield
SK10 4TG, UK
†Electronic supplementary information (ESI) available. See DOI:
10.1039/c2ob26035b
‡Both authors contributed equally to this work.
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Fig. 1 Homology model of the ATP-binding site of the DNA-dependent protein kinase (DNA-PK) used to guide inhibitor design. The 3D model
was constructed on the basis of the known X-ray crystal structure of PI3Kγ from the RCSB protein data bank (PDB ID: 1E7V) as a template, and with
the DNA-PK sequence from Swiss-Port (ID: PRKDC_DICDI) using Prime in the Maestro molecular modelling program (licensed from Schrödinger,
LGG). NU7441 (1) is represented in (a) an orthogonal, and (b) ‘in plane’ pose. (c) Representation of 5 in the orthogonal pose within the ATP-binding
domain.
chromen-4-one and dibenzothiophene rings and studied the
effect, upon biological activity, of alkylation at the 7-position of
the chromenone core (6–8). Accordingly, the homology model
suggested that substitution on the chromenone rather than on the
dibenzothiophene ring would be less detrimental to the inter-
action of the inhibitor with the ATP-binding pocket of DNA-PK.
As well as the prospect of refining the homology model further,
the synthesis of these DNA-PK inhibitors offered the opportu-
nity to further probe this region of the ATP-binding domain of
the enzyme.
Results and discussion
Synthesis of 7-substituted dibenzothiophenylchromen-4-ones
To introduce substituents at the chromen-4-one 7-position, we
used a similar approach to that recently reported.21 Alkylation of
phenol 9 with allyl bromide, followed by a Claisen rearrange-
ment furnished the 7-allylchromen-4-one derivative 11
(Scheme 1).30 Subsequent catalytic hydrogenation of 11 fol-
lowed by triflation gave the n-propyl intermediate 12 in 60%
6748 | Org. Biomol. Chem., 2012, 10, 6747–6757
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Scheme 1 Reagents and conditions: (i) allylbromide, K2CO3, CH3CN, reflux, 2.5 h, 95%; (ii) DMF, 160 °C, 18 h, 95%; (iii) H2, Pd/C, MeOH, r.t.,
85%; (iv) PhNTf2, Et3N, THF, reflux, 4 h, then r.t., 16 h, 70% for 12 and 80% for 13; (v) dibenzo[b,d]thiophen-4-ylboronic acid, Pd(PPh3)4 (5 mol%),
K2CO3, 1,4-dioxane, reflux, 18 h, 65%; (vi) H2, Pd/C, MeOH, r.t., 97%.
overall yield, while direct triflation of 11 afforded the corre-
sponding allyl analogue 13 in 80% yield. Suzuki–Miyaura
cross-coupling of the chromenone 13 with dibenzo[b,d]-
thiophen-4-ylboronic acid gave the 7-substituted analogue of
NU7441 (6). Further catalytic hydrogenation of 6 yielded the
corresponding n-propyl derivative 7.
of the members of each pair were established by polarimetry,
with the values confirming the resolution of the (−) and (+)
stereoisomers (Table 1). The atropisomers proved remarkably
stable to thermal racemisation. Thus, only chemical decompo-
sition occurred after heating atropisomer 6-(+) in mesitylene up
to 170 °C for 10 h, with no evidence of racemisation by chiral
HPLC analysis.
Introduction of a 7-methyl substituent on the chromenone core
was attempted via directed ortho-metallation (DoM),31–34 but
without any success. We therefore undertook the synthesis of the
chromenone scaffold, and introduced the methyl group as early
as possible in this multi-step approach (Scheme 2). Regio-
selective bromination of the methyl 2,3-dihydroxybenzoate 15
followed by methylation of the hydroxyl groups afforded the
bromide key intermediate 17.35 Subsequent palladium-mediated
Suzuki–Miyaura cross-coupling using trimethylboroxine gave
the desired methyl derivative 18 in excellent 91% yield.
The next steps of the synthesis followed the synthetic route we
previously published, involving judicious protection and
Rh-mediated deprotection of the hydroxyl with allyl groups.36
The resulting 8-hydroxy-7-methyl-2-morpholino-4H-chromen-
4-one 25 was converted into the corresponding triflate, and
cross-coupled with dibenzo[b,d]thiophen-4-ylboronic acid
assisted by microwave irradiation. The desired methyl derivative
8 was successfully isolated in 96% yield.
Biological evaluation
DNA-PK inhibitory activity was determined for the racemates
6–8, together with each of the corresponding pairs of separate
atropisomers and the results are summarised in Table 1. The
introduction of an allyl (6) or n-propyl (7) side chain at the
7-position of the chromen-4-one resulted in an approximately
9- and 3-fold reduction in potency of the racemic compounds,
respectively, compared with 1. Importantly, substitution with a
methyl group at the chromenone 7-position was tolerated, with
racemic 8 showing a 7-fold improvement in potency compared
with the parent compound 1. A comparison of the DNA-PK
inhibitory activity of each enantiomeric pair of chromenones 6–8
revealed that biological activity resided exclusively in the
(−)-atropisomer (‘eutomer’) in each case, with the antipodal
(+)-atropisomer (‘distomer’) proving to be inactive at 100 μM. In
the present study, the identification of resolvable atropisomers,
and the observation that only the (−)-enantiomer exhibits activity
against DNA-PK, has important implications for refining the
homology model.
Atropisomer resolution by chiral HPLC
Separation of atropisomers of chromenones 6–8 was achieved by
analytical chiral HPLC, where two distinct peaks were observed.
Acting as a control, NU7441 gave only a single peak under
these conditions because the lack of a chromenone substituent
lowers the barrier to rotation about the chromenone–dibenzothio-
phene σ-bond (Fig. 2). The excellent separation subsequently
achieved by semi-preparative chiral HPLC enabled the clear-cut
resolution of each pair of atropisomers of 6–8. Optical activities
Conclusions
By impeding DNA DSB repair, DNA-PK inhibitors have con-
siderable therapeutic potential as chemo- and radio-potentiating
agents in the therapy of cancer. As a prominent member of the
PIKK family of atypical serine–threonine kinases, DNA-PK is,
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Scheme 2 Reagents and conditions: (i) conc. H2SO4, MeOH, reflux, 18 h, 97% for 15 and 91% for 20; (ii) Br2, t-butylamine, DCM, toluene,
−78 °C, 2 h to r.t., 35%; (iii) MeI, K2CO3, acetone, reflux, 2 h, 90%; (iv) trimethylboroxine, PdCl2(dppf)·DCM, Cs2CO3, 1,4-dioxane, MW, 120 °C,
2 h, 91%; (v) Me3SiI, DCM, reflux, 24 h, 88%; (vi) allyl bromide, Cs2CO3, THF, reflux, 15 h, 84%; (vii) LDA, acetylmorpholine, THF, −10 °C,
1.5 h, then r.t., 1 h, 91%; (viii) Bu4NI, TiCl4, DCM, −78 °C, 30 min, then −78 °C to 0 °C, 1 h, 99%; (ix) Tf2O, DCM, 0 °C to r.t., 20 h, 51%; (x)
RhCl(PPh3)3, DABCO, EtOH, reflux, 2 h, 85%; (xi) PhNTf2, Cs2CO3, THF, MW, 100 °C, 20 min, 90%; (xii) dibenzo[b,d]thiophen-4-ylboronic acid,
PdCl2(d-t-bpf), Cs2CO3, 1,4-dioxane, MW, 80 °C, 30 min, 96%.
Fig. 2 Resolution of racemates 6, 7 and 8 by chiral HPLC. Conditions used for compound 6: Chiralpak IA, 250 × 10 mm, 5 μm, mobile phase: tert-
butyl methyl ether–ethanol (80 : 20); 7: Chiralpak IA, 250 × 10 mm, 5 μm, mobile phase: tert-butyl methyl ether–ethanol (75 : 25); 8: Chiralpak
AD-H, 250 × 10 mm, 5 μm, mobile phase: hexane–ethanol (75 : 25).
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Table 1 Inhibition of DNA-PK by 7-substituted chromen-4-one
derivatives (6–8)
1200 HPLC system (Agilent Technologies, Palo Alto, CA, USA)
equipped with a binary pump, an autosampler, a column oven
and a diode array detector and controlled by Agilent Chemsta-
tion software. Analyses were performed isocratically using
Daicel (Chiral Technologies Europe, Illkirch, France) columns.
Conditions used for compound 6: Chiralpak IA 250 × 4.6 mm,
5 μm, with a mobile phase consisting of tert-butyl methyl
ether–ethanol (80 : 20) at a flow rate of 1.0 mL min−1 with detec-
tion at 254 nm; conditions used for compound 7: Chiralpak
IA 250 × 4.6 mm, 5 μm, with a mobile phase consisting of
tert-butyl methyl ether–ethanol (75 : 25) at a flow rate of
1.0 mL min−1 with detection at 254 nm; conditions used for
compound 8: Chiralpak AD-H 250 × 4.6 mm, 5 μm with a
mobile phase consisting of hexane–ethanol (75 : 25) at a flow
rate of 1.0 mL min−1 with detection at 254 nm. Semi-preparative
chiral resolution was carried out using a Varian (Varian Inc.,
Walnut Creek, CA, USA) ProStar HPLC system equipped with
2 ProStar 210 solvent delivery modules, a ProStar 320 UV-Vis
detector and a ProStar 701 fraction collector and controlled by a
Varian Star Chromatography Workstation. Separations were per-
formed using Daicel columns. Conditions used for compound 6:
Chiralpak IA, 250 × 10 mm, 5 μm, with a mobile phase consist-
ing of tert-butyl methyl ether–ethanol (80 : 20) at a flow rate of
3.8 mL min−1 with detection at 254 nm; conditions used for
compound 7: Chiralpak IA, 250 × 10 mm, 5 μm, with a mobile
phase consisting of tert-butyl methyl ether–ethanol (75 : 25) at a
flow rate of 3.8 mL min−1 with detection at 254 nm; conditions
used for compound 8: Chiralpak AD-H, 250 × 10 mm, 5 μm,
with a mobile phase consisting of hexane–ethanol (75 : 25) at a
flow rate of 3.8 mL min−1 with detection at 254 nm. Petrol
refers to petroleum ether (bp 40–60 °C, reagent grade, Aldrich).
NMR spectra were recorded on a Bruker Spectrospin AC 300E
spectrometer (1H 300 MHz or 13C 75 MHz) or a Bruker Avance
III 500 spectrometer (1H 500 MHz or 13C 125 MHz). IR spectra
were recorded on a Bio-Rad FTS 3000MX diamond ATR.
Optical rotations were measured on a PolAAR3001 instrument.
LC-MS was carried out on a Micromass Platform LC system
operating in positive and negative ion electrospray mode (6, 7),
employing a 20 × 4.6 mm, Waters SymmetryShield RP18,
a 5 μm column and a 3.5 min gradient elution of 0.1%
formic acid and acetonitrile (5–95%) running at a flow rate
of 3 mL min−1 or a Waters Acquity SQD operating in posi-
tive and negative ion electrospray mode (8), employing a
50 × 2.1 mm, Waters Acquity UPLC BEH C18, 1.7 μm column
and a 1.5 min gradient elution of 0.1% formic acid and aceto-
nitrile (5–95%) running at a flow rate of 0.6 mL min−1. HRMS
were measured using a Finnigan MAT 95 XP or a Finnigan MAT
900 XLT by the EPSRC National Mass Spectrometry Service
Centre (Swansea).
DNA-PK inhibitiona
Compound number (IC50/μM)
R
Specific rotation
H
NU7441
6
6-(−)
6-(+)
0.028
0
0
Allyl
Allyl
Allyl
n-Propyl 7
n-Propyl 7-(−)
n-Propyl 7-(+)
Me
Me
Me
0.249b 0.011
0.125b 0.005
>10b
[αD]27.7 = −218
[αD]27.8 = +218
0
0.066 0.010
0.060 0.005
>10
0.005 0.003
0.002 0.001
7
[αD]27.9 = −202
[αD]28.0 = +202
0
8
8-(−)
8-(+)
[αD]21.2 = −254
[αD]27.5 = +254
a DNA-PK inhibitory activity was determined as described in ref. 37.
b DNA-PK inhibitory activity was determined as described in ref. 17.
in principle, amenable to the development of highly kinase-
selective ATP-competitive inhibitors, owing to the low sequence
homology of the ATP-binding domain with other protein
kinases.38 Nevertheless, troublesome off-target kinase-inhibitory
activity associated with currently available small-molecule
DNA-PK inhibitors, including 2, continues to represent an
obstacle to preclinical development. As such, there is a require-
ment for inhibitors that combine good pharmaceutical properties
with high potency and selectivity for DNA-PK over related
kinases, most notably members of the PI 3-kinase family. In this
paper, we report the results of ongoing studies designed to
improve the selectivity of chromenone-based inhibitors through
substitution on the core chromen-4-one. The introduction of
alkyl substituents at the chromenone 7-position has enabled the
resolution of relatively stable atropisomers, which exhibit differ-
ential DNA-PK inhibitory activity and show potency comparable
to, and in one case (methyl substitution, compound 8) superior
to, the parent compound 1. Studies are in progress to elucidate
the absolute configuration of the biologically active (−)-atrop-
isomers, prior to conducting further studies with the DNA-PK
homology model. The possibility of introducing water-solubil-
ising substituents on the dibenzothiophene ring of atropisomeric
DNA-PK inhibitors, analogously to that achieved with 2, is also
under consideration.
8-Hydroxy-2-morpholino-4H-chromen-4-one (9). A solution
of 2-morpholino-4-oxo-4H-chromen-8-yl trifluoromethanesulfo-
nate (2 g, 5.3 mmol) and 2 M NaOH (26 mL) in methanol
(10 mL) and 1,4-dioxane (20 mL) was stirred at room tempera-
ture overnight. The solvent was removed from the reaction
mixture in vacuo. The resulting crude solid was purified by
medium pressure column chromatography (EtOAc–MeOH 9 : 1),
followed by recrystallisation from MeOH, yielding the title com-
pound as a white crystalline solid (1.01 g, 78%): Rf = 0.36
Experimental
Materials and methods
Solvents were purchased as anhydrous. Reactions needing micro-
wave irradiation were carried out in an Initiator™ Sixty Biotage
apparatus. Chiral HPLC analysis was performed on an Agilent
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(EtOAc–MeOH 9 : 1); mp: 240–242 °C; IR (cm−1) 2951, 2866,
1638, 1575, 1448, 1410, 1350, 1243, 1114, 1028; λmax (EtOH)/
nm 303; 1H NMR (300 MHz, MeOD-d4) δ 3.62 (4H, t, J =
4.4 Hz, CH2–morpholine), 3.73 (4H, t, J = 4.4 Hz, CH2–mor-
pholine), 5.85 (1H, s, H-3), 7.24–7.27 (2H, m, H–Ar), 7.36 (1H,
dd, J = 2.2 and 7.0 Hz, H–Ar); 13C NMR (75 MHz, MeOD-d4)
δ 45.9 (CH2–N–morpholine), 67.1 (CH2–O–morpholine), 87.1
(C-3), 115.6 (C-6), 119.9 (C-8), 124.3 (C-5), 126.1 (C-7), 145.9
(C-10), 148.8 (C-9), 164.4 (C-2), 180.0 (C-4); MS(ES+) m/z =
248.1 [M + H]+; HRMS calcd for C13H14NO4 [M + H]+
248.0923, found 248.0917.
2-Morpholino-4-oxo-7-propyl-4H-chromen-8-yl trifluoro-
methanesulfonate (12). To an ice bath cooled solution of
7-allyl-8-hydroxy-2-morpholino-4H-chromen-4-one (0.157 g,
0.547 mmol) in methanol (35 mL) was added Pd/C (10%,
0.048 g). The reaction mixture was stirred at room temperature
for 16 h under H2 atmosphere. The reaction mixture was filtered
over a pad of celite and concentrated in vacuo, recrystallisation
from methanol yielded 8-hydroxy-2-morpholino-7-propyl-4H-
chromen-4-one as an off-white solid (0.134 g, 85%). A solution
of 8-hydroxy-2-morpholino-7-propyl-4H-chromen-4-one inter-
mediate (0.064 g, 0.219 mmol), triethylamine (0.1 mL,
0.658 mmol) and N-phenyl-bis(trifluoromethanesulfonimide)
(0.117 g, 0.329 mmol) in THF (12 mL) was heated at reflux for
4 h. The mixture was subsequently stirred at room temperature
for 16 h. The reaction mixture was diluted with water (10 mL)
and extracted with DCM (3 × 15 mL). The combined organic
layers were dried (MgSO4) and concentrated in vacuo. The crude
product was purified by medium pressure column chromato-
graphy (EtOAc–MeOH 95 : 5) yielding the title compound as a
pale brown crystalline solid (0.065 g, 70%): Rf = 0.47 (EtOAc–
MeOH 95 : 5); mp: 115–116 °C; IR (cm−1) 2924, 2853, 1597,
1550, 1449, 1409, 1253, 1211, 1109, 1012, 979, 875, 802; λmax
8-Allyloxy-2-morpholino-4H-chromen-4-one (10). To a solu-
tion of 8-hydroxy-2-morpholino-4H-chromen-4-one (0.467 g,
1.89 mmol) in acetonitrile (20 mL) containing suspended potas-
sium carbonate (0.522 g, 3.78 mmol) was added dropwise allyl
bromide (0.33 mL, 3.78 mmol). The mixture was heated at
reflux for 2.5 h, cooled and filtered through a pad of celite and
concentrated in vacuo. The residue was purified by medium
pressure column chromatography (EtOAc–MeOH 9 : 1) yielding
the title compound as a pale yellow solid (0.506 g, 95%): Rf =
0.55 (EtOAc–MeOH 9 : 1); IR (cm−1) 2951, 2866, 1638, 1575,
1448, 1410, 1350, 1243, 1114, 1028; λmax (EtOH)/nm 235;
1H NMR (500 MHz, MeOD-d4) δ 3.64 (4H, t, J = 5.1 Hz, CH2–
morpholine), 3.83 (4H, t, J = 5.1 Hz, CH2–morpholine),
4.72–4.73 (2H, m, CH2–CHvCH2), 5.32 (1H, dd, J = 1.6 and
10.6 Hz, CH2–CHvCH2cis), 5.47 (1H, dd, J = 1.6 and 17.4 Hz,
CH2–CHvCH2trans), 5.61 (1H, s, H-3), 6.13 (1H, ddt, J = 5.1,
10.6 and 17.4 Hz, CH2–CHvCH2), 7.32–7.33 (2H, m, H–Ar),
7.59–7.62 (1H, m, H–Ar); 13C NMR (75 MHz, MeOD-d4)
δ 46.4 (CH2–N–morpholine), 67.5 (CH2–O–morpholine), 71.7
(CH2–CHvCH2), 87.7 (C-3), 117.6 (C–Ar–H), 118.0 (C–Ar–
H), 118.4 (CH2–CHvCH2), 125.0 (C-5), 126.2 (C–Ar–H),
134.7 (CH2–CHvCH2), 145.9 (C-10), 148.8 (C-9), 164.8 (C-2),
179.8 (C-4); MS(ES+) m/z = 288.1 [M + H]+; HRMS calcd for
C16H18NO4 [M + H]+ 288.1236, found 288.1230.
1
(EtOH)/nm 311, 213; H NMR (500 MHz, MeOD-d4) δ 1.00
(3H, t, J = 7.5 Hz, CH2–CH2–CH3) 1.72 (2H, sextet, J = 7.5 Hz,
CH2–CH2–CH3), 2.80 (2H, t, J = 7.4 Hz, CH2–CH2–CH3), 3.68
(4H, t, J = 4.0 Hz, CH2–morpholine), 3.82 (4H, t, J = 4.0 Hz,
CH2–morpholine), 5.63 (1H, s, H-3), 7.46 (1H, d, J = 8.1 Hz,
H–Ar), 8.01 (1H, d, J = 8.1 Hz, H–Ar); 13C NMR (125 MHz,
MeOD-d4) δ 14.0 (CH2–CH2–CH3), 24.3 (CH2–CH2–CH3),
32.9 (CH2–CH2–CH3), 46.5 (CH2–N–morpholine), 67.0 (CH2–
O–morpholine), 87.6 (C-3), 121.8 (C-5), 124.6 (C-6), 126.1
(C-7), 135.7 (C-8), 141.9 (C-9), 147.3 (C-10), 164.1 (C-2),
177.5 (C-4); MS(ES+) m/z = 422.2 [M + H]+; HRMS calcd for
C17H19F3NO6S [M + H]+ 422.0885, found 422.0874.
7-Allyl-2-morpholino-4-oxo-4H-chromen-8-yl trifluoromethane-
sulfonate (13). A solution of 7-allyl-8-hydroxy-2-morpholino-
4H-chromen-4-one (0.300 g, 1.05 mmol), triethylamine
(0.53 mL, 3.80 mmol) and N-phenyl-bis(trifluoromethanesulfo-
nimide) (1.36 g, 3.80 mmol) in THF (10 mL) was heated at
reflux for 4 h. The mixture was subsequently stirred at room
temperature for 16 h. The reaction mixture was diluted with
water (50 mL) and extracted with DCM (3 × 25 mL). The com-
bined organic layers were dried (Na2SO4) and concentrated
in vacuo. The crude product was purified by medium pressure
column chromatography (EtOAc–MeOH 95 : 5) yielding the title
compound as a white crystalline solid (0.349 g, 80%): Rf = 0.65
(EtOAc–MeOH 95 : 5); IR (cm−1) 3067, 2948, 2865, 1601,
7-Allyl-8-hydroxy-2-morpholino-4H-chromen-4-one (11). A
solution
of
8-allyloxy-2-morpholino-4H-chromen-4-one
(0.443 g, 1.54 mmol) in DMF (10 mL) was heated at 160 °C
overnight. The solvent was then removed in vacuo. Purification
by medium pressure column chromatography (EtOAc–MeOH
9 : 1) followed by recrystallisation from MeOH–petrol 1 : 1
yielded the title compound as a white solid (0.420 g, 95%): Rf =
0.50 (EtOAc–MeOH 9 : 1); IR (cm−1) 2917, 2859, 1605, 1548,
1418, 1359, 1245, 1191, 1113, 1030; λmax (EtOH)/nm 260;
1H NMR (500 MHz, MeOD-d4) δ 3.52 (2H, d, J = 6.5 Hz,
CH2–CHvCH2), 3.66–3.68 (4H, m, CH2–morpholine), 3.82
(4H, t, J = 4.9 Hz, CH2–morpholine), 5.04–5.09 (2H, m,
CH2–CHvCH2), 5.56 (1H, s, H-3), 5.97–6.05 (1H, m,
CH2–CHvCH2), 7.14 (1H, d, J = 8.2 Hz, H–Ar), 7.47 (1H, d,
J = 8.2 Hz, H–Ar); 13C NMR (125 MHz, MeOD-d4) δ 35.2
(CH2–CHvCH2), 46.1 (CH2–N–morpholine), 67.1 (CH2–O–
morpholine), 87.1 (C-3), 116.3 (C-6), 118.0 (CH2–CHvCH2),
124.4 (C-5), 127.1 (C-7), 134.2 (CH2–CHvCH2), 137.2 (C-8),
145.2 (C-10), 148.3 (C-9), 164.5 (C-2), 179.7 (C-4); MS(ES+)
m/z = 288.1 [M + H]+; HRMS calcd for C16H18NO4 [M + H]+
288.1236, found 288.1230.
1
1550, 1415, 1202, 1134, 1110; λmax (EtOH)/nm 314; H NMR
(500 MHz, CDCl3) δ 3.54 (2H, d, J = 6.6 Hz, CH2–CHvCH2),
3.58 (4H, t, J = 4.9 Hz, CH2–morpholine), 3.83 (4H, t, J =
4.9 Hz, CH2–morpholine), 5.16 (1H, dd, J = 1.4 and 17.0 Hz,
CH2–CHvCH2trans), 5.22 (1H, dd, J = 1.3 and 10.0 Hz, CH2–
CHvCH2cis), 5.55 (1H, s, H-3), 5.85–5.93 (1H, m, CH2–
CHvCH2), 7.30 (1H, d, J = 8.3 Hz, H–Ar), 8.09 (1H, d, J =
8.3 Hz, H–Ar); 13C NMR (125 MHz, CDCl3) δ 33.8 (CH2–
CHvCH2), 45.3 (CH2–N–morpholine), 66.0 (CH2–O–morpho-
line), 87.6 (C-3), 118.53 (CH2–CHvCH2), 118.56 (1C, q, J =
320 Hz, OSO2CF3), 123.4 (C-5), 125.1 (C-6), 126.4 (C-7),
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133.6 (CH2–CHvCH2), 134.2 (C-9), 137.5 (C-8), 146.1 (C-10),
162.3 (C-2), 175.5 (C-4); MS(ES+) m/z = 420.2 [M + H]+;
HRMS calcd for C17H17F3NO6S [M + H]+ 420.0729, found
420.0720.
morpholine), 65.8 (CH2–O–morpholine), 86.8 (C-3), 121.0
(C–Ar), 121.3 (C–Ar), 122.0 (C–Ar), 123.1 (C–Ar), 124.8
(C–Ar), 124.9 (C–Ar), 125.5 (C–Ar), 126.3 (C–Ar), 127.3 (C–
Ar), 127.4 (C–Ar), 128.3 (C–Ar), 130.5 (C–Ar), 135.7 (C–Ar),
135.9 (C–Ar), 139.5 (C–Ar), 140.9 (C–Ar), 146.8 (C–Ar), 151.3
(C–Ar), 162.4 (C-2), 177.4 (C-4); MS(ES+) m/z = 455.6
[M + H]+; HRMS calcd for C28H26NO3S [M + H]+ 456.1628
found 456.1626.
7-Allyl-8-(dibenzo[b,d]thiophen-4-yl)-2-morpholino-4H-chromen-
4-one (6). Potassium carbonate (0.100 g, 0.715 mmol) and
Pd(PPh3)4 (0.014 g, 0.012 mmol) were sequentially added to a
degassed solution of 7-allyl-2-morpholino-4-oxo-4H-chromen-
8-yl trifluoromethanesulfonate (0.100 g, 0.238 mmol), dibenzo-
[b,d]thiophen-4-ylboronic acid (0.109 g, 0.477 mmol) in an-
hydrous 1,4-dioxane (5 mL). The reaction mixture was heated at
reflux for 18 h. Upon cooling, the mixture was filtered through a
pad of celite and the organic solvent removed in vacuo. The
crude product was purified by medium pressure column
chromatography (EtOAc–MeOH 95 : 5) to yield the title com-
pound as an off-white solid (0.070 g, 65%): Rf = 0.38 (EtOAc–
MeOH 95 : 5); mp: 204–205 °C; IR (cm−1) 2951, 2919, 2848,
1620, 1584, 1555, 1410, 1381, 1350, 1227, 1107; λmax
2,3-Dihydroxymethylbenzoate (15). To a solution of the
2,3-dihydroxybenzoic acid (1 g, 6.5 mmol) in MeOH (10 mL) at
0–5 °C was added dropwise conc. sulfuric acid (0.7 mL). The
reaction mixture was heated to reflux and stirred for 18 h. The
solvent was removed from the reaction mixture in vacuo, diluted
with EtOAc and a saturated aqueous solution of NaHCO3 was
added until effervescing ceased. The aqueous layer was extracted
into EtOAc, the combined organic layers were dried (MgSO4).
The solvent was removed in vacuo to give the crude product that
was purified by medium pressure column chromatography
(petrol–EtOAc 9 : 1) to yield the title compound as beige crystals
(1.06 g, 97%): Rf = 0.24 (petrol–EtOAc 9 : 1); mp: 81–83 °C
(lit. 81 °C);39 IR (cm−1) 3456, 2152, 1669, 1458, 1433, 1311,
1260, 1191, 1147, 1005, 907, 834, 753, 718; λmax (EtOH)/nm
249, 321; 1H NMR (500 MHz, CDCl3) δ 3.88 (3H, s,
COOCH3), 5.65 (1H, s, OH), 6.72 (1H, dd, J = 7.9, 8.0 Hz,
H–Ar), 7.04 (1H, d, J = 7.9 Hz, H–Ar), 7.28 (1H, d, J = 8.0 Hz,
H–Ar), 10.82 (1H, s, OH); 13C NMR (125 MHz, CDCl3) δ 52.6
(OCH3), 112.5 (C-1), 119.4 (C-5), 119.9 (C-4), 120.7 (C-6),
145.2 (C-3), 149.0 (C-2), 170.9 (CvO); MS (ES+) m/z = 169.1
[M + H]+; HRMS calcd for C8H9O4 [M + H]+ 169.0495, found
169.0491.
1
(EtOH)/nm 236, 313; H NMR (500 MHz, CDCl3) δ 2.85–2.95
(4H, m, CH2–morpholine), 3.22–3.36 (2H, m, CH2–CHvCH2),
3.38–3.90 (4H, m, CH2–morpholine), 4.88 (1H, dd, J = 1.5 and
19.0 Hz, CH2–CHvCH2trans), 4.97 (1H, dd, J = 1.4 and
10.0 Hz, CH2–CHvCH2cis), 5.50 (1H, s, H-3), 5.76–5.85 (1H,
m, CH2–CHvCH2), 7.37 (1H, dd, J = 1.0 and 7.3 Hz, H–Ar),
7.41 (1H, d, J = 8.2 Hz), 7.46–7.52 (2H, m, H–Ar), 7.58 (1H,
dd, J = 7.4 and 7.5 Hz, H–Ar), 7.79 (1H, d, J = 7.0 Hz, H–Ar),
8.20–8.23 (3H, m, H–Ar); 13C NMR (125 MHz, CDCl3) δ 37.8
(CH2–CHvCH2), 44.5 (CH2–N–morpholine), 65.8 (CH2–O–
morpholine), 86.8 (C-3), 117.0 (CH2–CHvCH2), 121.3 (C–Ar),
121.4 (C–Ar), 122.0 (C–Ar), 123.9 (C–Ar), 124.8 (C–Ar), 124.9
(C–Ar), 125.6 (C–Ar), 126.4 (C–Ar), 127.3 (C–Ar), 127.5
(C–Ar), 128.2 (C–Ar), 130.0 (C–Ar), 135.6 (C–Ar), 135.9
(C–Ar), 136.2 (CH2–CHvCH2), 139.4 (C–Ar), 140.7 (C–Ar),
144.0 (C–Ar), 151.3 (C-10), 162.3 (C-2), 177.1 (C-4); MS
(ES+) m/z = 454.3 [M + H]+; HRMS calcd for C28H24NO3S
[M + H]+ 454.1471, found 454.1474.
2,3-Dihydroxy-4-bromo methylbenzoate (16). Bromine (1.1 mL,
21.4 mmol) was added dropwise to a solution of tert-butylamine
(3.7 mL, 35.7 mmol) in toluene (36 mL) and DCM (6 mL) at
−60 °C. The reaction mixture was cooled to −78 °C and
2,3-dihydroxymethylbenzoate (3.0 g, 17.8 mmol) in DCM
(15 mL) was added dropwise over 20 min. The reaction mixture
was stirred at −78 °C for 30 min and then warmed to room
temperature slowly. The reaction mixture was diluted with
EtOAc (50 mL) and washed with 1 M HCl (2 × 50 mL). The
aqueous phase was extracted into EtOAc and the combined
organic layers were washed with brine, dried (Na2SO4) and con-
centrated in vacuo. The crude product was purified by medium
pressure column chromatography (petrol–EtOAc 9 : 1) yielding
the title compound as a white solid (1.55 g, 35%): Rf = 0.26
(petrol–EtOAc 9 : 1); mp: 76–78 °C; IR (cm−1) 3383, 3154,
2921, 2852, 1661, 1605, 1442, 1309, 1184, 1151, 1125, 1003,
8-(Dibenzo[b,d]thiophen-4-yl)-2-morpholino-7-propyl-4H-
chromen-4-one (7). To an ice bath cooled solution of 7-allyl-
8-(dibenzo[b,d]thiophen-4-yl)-2-morpholino-4H-chromen-4-one
(0.038 g, 0.084 mmol) in methanol (15 mL) was added Pd/C
(10%, 0.019 g). The reaction mixture was stirred at room temp-
erature for 18 h under H2 atmosphere. The reaction mixture was
filtered over a pad of celite and concentrated in vacuo, recrystalli-
sation from MeOH gave the title compound as a white crystalline
solid (0.037 g, 97%); Rf = 0.63 (EtOAc–MeOH 95 : 5); mp
219–220 °C; IR (cm−1) 3066, 2950, 2922, 2862, 1624, 1587,
155, 1411, 1387, 1298, 1246, 1109; λmax (EtOH)/nm 235, 311;
1H NMR (500 MHz, CDCl3) δ 0.73 (3H, t, J = 7.4 Hz,
CH2–CH2–CH3), 1.48 (2H, sextet, J = 7.5 Hz, CH2–CH2–CH3),
2.46 (1H, dt, J = 7.5 and 13.7 Hz, CH2–CH2–CH3), 2.61 (1H,
dt, J = 7.5 and 13.7 Hz, CH2–CH2–CH3), 2.80–2.91 (4H, m,
CH2–morpholine), 3.31–3.39 (4H, m, CH2–morpholine), 5.45
(1H, s, H-3), 7.37 (1H, dd, J = 1.0 and 7.3 Hz, H–Ar), 7.0 (1H,
d, J = 8.2 Hz, H–Ar), 7.43–7.50 (2H, m, H–Ar), 7.56 (1H, dd,
J = 7.5 and 7.6 Hz, H–Ar), 7.75–7.79 (1H, m, H–Ar), 8.15–8.22
(3H, m, H–Ar); 13C (125 MHz, CDCl3) δ 14.1 (CH2–CH2–CH3),
24.4 (CH2–CH2–CH3), 35.6 (CH2–CH2–CH3), 44.5 (CH2–N–
1
872, 799, 761, 727; λmax (EtOH)/nm 215, 259, 317; H NMR
(500 MHz, CDCl3) δ 3.88 (3H, s, COOCH3), 5.96 (1H, s, OH),
6.97 (1H, d, J = 8.7 Hz, H–Ar), 7.19 (1H, d, J = 8.7 Hz, H–Ar),
11.03 (1H, s, OH); 13C NMR (125 MHz, CDCl3) δ 52.8
(OCH3), 111.6 (C-1), 114.6 (C-4), 120.8 (C-6), 123.0 (C-5),
142.9 (C-3), 149.3 (C-2), 170.5 (CvO); MS (ES+) m/z = 247.1,
249.1 (100%) [M + H]+, 215.0, 217.0 (50%); HRMS calcd for
C8H8BrO4 (79Br) [M + H]+ 246.9600, found 246.9604.
2,3-Dimethoxy-4-bromo methylbenzoate (17). A mixture of
2,3-dihydroxy-4-bromo methylbenzoate (2.2 g, 9.0 mmol),
potassium carbonate (3.7 g, 27.0 mmol), methyl iodide (5.6 mL,
This journal is © The Royal Society of Chemistry 2012
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90.0 mmol) and acetone (50 mL) was heated at reflux for 2.5 h,
cooled to room temperature, a saturated aqueous solution of
NaHCO3 (30 mL) was introduced and the reaction mixture
stirred for 10 min. The reaction mixture was extracted into
EtOAc, the organic phase was washed with water, dried
(MgSO4) and concentrated in vacuo. The crude product was
purified by medium pressure column chromatography (petrol–
EtOAc 9 : 1) yielding the title compound as a colourless oil
(2.2 g, 90%): Rf = 0.37 (petrol–EtOAc 9 : 1); IR (cm−1) 2942,
1729, 1576, 1457, 1398, 1285, 1236, 1139, 1027, 1003, 881,
1 : 1); mp: 195–197 °C; IR (cm−1) 3514, 2598, 1624, 1457,
1387, 1305, 1266, 1232, 1157, 1045, 967, 861, 765, 734; λmax
1
(EtOH)/nm 211, 249, 308; H NMR (500 MHz, CDCl3) δ 2.03
(3H, s, CH3), 6.43 (1H, d, J = 8.1 Hz, H–Ar), 7.05 (1H, d,
J = 8.1 Hz, H–Ar); 13C NMR (125 MHz, CDCl3) δ 16.1 (CH3),
113.1 (C-1), 121.6 (C-5), 126.0 (C-6), 139.7 (C-4), 147.4 (C-3),
156.4 (C-2), 173.7 (CvO); MS (ES+) m/z = 169.2 [M + H]+;
HRMS calcd for C8H9O4 [M + H]+ 169.0495, found 169.0491.
2,3-Dihydroxy-4-methyl methylbenzoate (20). To a solution of
the 2,3-dihydroxy-4-methylbenzoic acid (0.320 g, 0.19 mmol) in
MeOH (20 mL) at 0–5 °C was added dropwise conc. sulfuric
acid (0.25 mL). The reaction mixture was heated to reflux and
stirred for 18 h. The solvent was removed from the reaction
mixture in vacuo, diluted with EtOAc and a saturated aqueous
solution of NaHCO3 was added until effervescing ceased. The
aqueous layer was extracted into EtOAc, the combined organic
layers were dried (MgSO4). The solvent was removed in vacuo
to give the crude product that was purified by medium pressure
column chromatography (petrol–EtOAc 9 : 1) to yield the title
compound as an off-white solid (0.314 g, 91%): Rf = 0.27
(petrol–EtOAc 9 : 1); mp: 41–43 °C; IR (cm−1) 3482, 2967,
2922, 1668, 1433, 1305, 1248, 1197, 1156, 1049, 995, 943, 902,
766, 735, 703; λmax (EtOH)/nm 210, 251, 312; 1H NMR
(500 MHz, CDCl3) δ 2.22 (3H, s, CH3), 3.87 (3H, s, OCH3),
5.63 (1H, s, OH), 6.59 (1H, d, J = 8.2 Hz, H–Ar), 7.19 (1H, d,
J = 8.2 Hz, H–Ar), 10.78 (1H, s, OH); 13C NMR (125 MHz,
CDCl3) δ 16.4 (CH3), 52.6 (OCH3), 120.5 (C-6), 121.1 (C-5),
123.8 (C-1), 130.6 (C-4), 142.5 (C-3), 148.4 (C-2), 172.2
(CvO); MS (ES+) m/z = 183.2 [M + H]+; HRMS calcd for
C9H11O4 [M + H]+ 183.0652, found 183.0647.
1
852, 784, 748; λmax (EtOH)/nm 210, 240; H NMR (500 MHz,
CDCl3) δ 3.83 (3H, s, OCH3), 3.84 (3H, s, COOCH3), 3.88 (3H,
s, OCH3), 7.27 (1H, d, J = 8.5 Hz, H–Ar), 7.34 (1H, d, J =
8.5 Hz, H–Ar); 13C NMR (125 MHz, CDCl3) δ 52.3
(COOCH3), 60.8 (OCH3), 61.8 (OCH3), 122.6 (C-4), 125.5
(C-1), 126.6 (C-6), 127.8 (C-5), 151.7 (C-3), 154.3 (C-2), 165.7
(CvO); MS (ES+) m/z = 243.1, 245.1 (100%) [M − 2Me]+,
275.1, 277.1 (20%) [M + H]+; HRMS calcd for C10H1279BrO4
[M + H]+ 274.9913, found 274.9919.
2,3-Dimethoxy-4-methyl methylbenzoate (18). PdCl2(dppf)·
DCM (0.3 g, 5 mol%) was added to a degassed solution of
2,3-dimethoxy-4-bromo methylbenzoate (2.1 g, 7.5 mmol), tri-
methyl boroxine (1.4 mL, 9.7 mmol) and caesium carbonate
(3.4 g, 10.5 mmol) in 1,4-dioxane (10 mL). The mixture was
heated under microwave irradiation at 120 °C for 2 h. The reac-
tion mixture was diluted with EtOAc (50 mL) and washed with a
saturated aqueous solution of NH4Cl (50 mL). The combined
organic layers were dried (MgSO4), the solvent was removed
in vacuo to give the crude product that was purified by medium
pressure column chromatography (petrol–EtOAc 9 : 1) to yield
the title compound as a colourless oil (1.4 g, 91%): Rf = 0.35
(petrol–EtOAc 9 : 1); IR (cm−1) 2943, 1727, 1604, 1462, 1402,
1260, 1204, 1133, 1064, 1023, 998, 924, 875, 791, 756, 684;
2,3-Diallyloxy-4-methyl methylbenzoate (21). A mixture of
2,3-dihydroxy-4-methyl methylbenzoate (0.314 g, 1.72 mmol),
allyl bromide (0.60 mL, 0.70 mmol) and caesium carbonate
(1.45 g, 4.46 mmol) in THF (10 mL) was heated at reflux for
15 h. The reaction mixture was then cooled to room temperature,
diluted with EtOAc (15 mL) and washed with water (10 mL).
The aqueous phase was re-extracted with EtOAc (2 × 10 mL),
the combined organic layers were dried (MgSO4) and concen-
trated in vacuo. The crude product was purified by medium
pressure column chromatography (petrol–EtOAc 9 : 1) to give
the title compound as a colourless oil (0.379 g, 84%): Rf = 0.30
(petrol–EtOAc, 9 : 1); IR (cm−1) 1949, 1728, 1603, 1414, 1261,
1197, 1135, 1059, 986, 923, 829, 787, 756, 710; λmax
1
λmax (EtOH)/nm 207, 240; H NMR (500 MHz, CDCl3) δ 2.23
(3H, s, CH3), 3.78 (3H, s, OCH3), 3.83 (3H, s, COOCH3), 3.84
(3H, s, OCH3), 6.87 (1H, d, J = 8.5 Hz, H–Ar), 7.37 (1H, d,
J = 8.5 Hz, H–Ar); 13C NMR (125 MHz, CDCl3) δ 16.2 (CH3),
52.0 (COOCH3), 60.3 (OCH3), 61.4 (OCH3), 123.6 (C-1), 125.5
(C-5), 125.7 (C-6), 137.5 (C-4) 153.3 (C-3), 153.4 (C-2), 166.4
(CvO); MS (ES+) m/z = 179.2 (100%) [M − 2Me]+, 199.1
(70%); HRMS calcd for C11H15O4 [M + H]+ 211.0965, found
211.0964.
2,3-Dihydroxy-4-methylbenzoic acid (19). Iodotrimethylsilane
(4.2 mL, 30.9 mmol) was added dropwise to a solution of
2,3-dimethoxy-4-methyl methylbenzoate (1.0 g, 5.2 mmol) in
DCM (10 mL) and the reaction mixture heated at reflux for 23 h.
In parallel, three reactions were completed, the reaction mixtures
were cooled and to each reaction mixture MeOH (5 mL) was
added to destroy the excess silane. The three reaction mixtures
were combined and the organic solvent was removed in vacuo.
The crude product was diluted with EtOAc (50 mL) and
extracted with 1 M NaOH (15 mL). The resulting aqueous phase
was acidified with 1 M HCl to pH 2 and extracted into EtOAc.
The combined organic layers were dried (MgSO4) and the
solvent was removed in vacuo, the title compound was isolated
as a brown solid (2.3 g, 88%) and was used without further
purification: Rf = 0.20 (Si-C18, H2O–MeOH 0.1% formic acid
1
(EtOH)/nm 210, 239, 285; H NMR (500 MHz, CDCl3) δ 2.23
(3H, s, CH3), 3.81 (3H, s, OCH3), 4.44 (2H, d, J = 3.5 Hz,
CH2–CHvCH2), 4.49 (2H, d, J = 5.9 Hz, CH2–CHvCH2),
5.17 (2H, dd, J = 1.5 and 10.2 Hz, CH2–CHvCH2cis) 5.30
(2H, dd, J = 1.5 and 17.1, Hz, CH2–CHvCH2trans), 5.97–6.10
(2H, m, CH2–CHvCH2), 6.88 (1H, d, J = 8.0 Hz, H–Ar), 7.39
(1H, d, J = 8.0 Hz, H–Ar); 13C NMR (125 MHz, CDCl3)
δ 16.6 (CH3), 52.1 (COOCH3), 73.8 (CH2CHvCH2), 75.0
(CH2CHvCH2), 117.8 (CH2CHvCH2), 117.9 (CH2CHvCH2),
124.0 (C-1), 125.7 (CH2CHvCH2), 125.8 (CH2CHvCH2),
134.0 (2C, C-2 and C-3), 137.8 (C-4), 151.3 (C-3), 152.1 (C-2),
166.5 (CvO); MS (ES+) m/z = 263.2 [M + H]+; HRMS calcd
for C15H19O4 [M + H]+ 263.1278, found 263.1280.
6754 | Org. Biomol. Chem., 2012, 10, 6747–6757
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1-(2,3-Bis(allyloxy)-4-methylphenyl)-3-morpholinopropane-
1,3-dione (22). To a solution of diisopropylamine (0.80 mL,
5.7 mmol) in THF (20 mL) at −78 °C was added dropwise
nBuLi (2.5 M in hexanes, 2.28 mL, 5.7 mmol), the reaction
mixture was warmed to 0 °C and stirred for 20 min. The reaction
mix was cooled to −10 °C, acetyl morpholine (0.44 mL,
3.8 mmol) was added dropwise and stirring was continued at
−10 °C for 90 min. To the reaction mixture was added dropwise
2,3-diallyloxy-4-methyl methylbenzoate (0.500 g, 1.9 mmol) in
THF (5 mL) and stirring continued at room temperature for 1 h.
The reaction mixture was diluted with water, acidified to pH 1
with a 1 M HCl and extracted with DCM (2 × 15 mL). The com-
bined organic layers were dried (MgSO4) and concentrated
in vacuo. The crude product was purified by medium pressure
column chromatography (DCM–MeOH 95 : 5) to give the title
compound as a colourless oil (0.690 g, quant.): Rf = 0.46
(DCM–MeOH 95 : 5); IR (cm−1) 2965, 2923, 2856, 2358, 1621,
1413, 1232; λmax (EtOH)/nm 260, 300; 1H NMR (500 MHz,
CDCl3) δ 2.23 (2.1H, s, CH3), 2.29 (2.4H, s, CH3), 2.30 (3H, s,
CH3), 3.48–3.70 (20H, m, CH2–morpholine), 4.14 (2H, s,
C(O)CH2C(O)), 4.35 (1.4H, d, J = 5.6 Hz, CH2–CHvCH2),
4.47 (2H, d, J = 5.7 Hz, CH2–CHvCH2), 4.49–4.51 (3.2H, m,
CH2–CHvCH2), 4.63 (2H, d, J = 5.7 Hz, CH2–CHvCH2),
4.67 (1.4H, d, J = 5.6 Hz, CH2–CHvCH2), 5.21–5.28 (4.9H, m,
CH2–CHvCH2), 5.34–5.46 (5.1H, m, CH2–CHvCH2),
6.02–6.17 (5H, m, CH2–CHvCH2), 6.26 (0.8H, s, enolic CH),
6.28 (0.7H, s, enolic CH), 6.91 (0.7H, d, J = 8.1 Hz, H–Ar),
6.98 (1.8H, d, J = 8.0 Hz, H–Ar), 7.35 (0.7H, d, J = 8.1 Hz,
H–Ar), 7.40 (1H, d, J = 8.0 Hz, H–Ar), 7.48 (0.8H, d, J =
8.0 Hz, H–Ar), 15.1 (0.7H, s, enolic OH); 13C NMR (125 MHz,
CDCl3) δ 16.2, 16.6, 16.7, 41.6, 41.9, 42.0, 42.2, 46.8, 46.9,
47.0, 49.5, 66.7, 66.8, 66.9, 66.96, 66.99, 67.0, 73.2, 73.3, 73.8,
73.9, 74.0, 74.3, 74.7, 88.3, 117.2, 117.4, 117.7, 117.8, 118.1,
118.4, 123.8, 124.9, 125.7, 126.2, 126.3, 127.4, 131.0, 132.4,
133.8, 134.1, 134.2, 134.5, 135.7, 137.1, 139.0, 148.1, 150.3,
150.57, 150.59, 151.0, 151.5, 166.4, 169.2, 170.6, 194.9;
MS (ES+) m/z = 360.1 [M + H]+; HRMS calcd for C20H26NO5
[M + H]+ 360.1805, found 360.1803.
CH2–CHvCH2), 5.18 (1H, dd, J = 1.3 and 10.3 Hz, CH2–
CHvCH2cis), 5.32 (1H, dd, J = 1.3 and 17.2 Hz, CH2–
CHvCH2trans), 6.04 (1H, ddt, J = 5.9, 10.3 and 17.2 Hz CH2–
CHvCH2), 6.67 (1H, d, J = 8.3 Hz, H–Ar), 7.41 (1H, d, J =
8.3 Hz, H–Ar), 12.1 (1H, br s, OH); 13C NMR (125 MHz,
CDCl3) δ 17.0 (CH3), 42.3 (CH2–N–morpholine), 45.2 (C(O)-
CH2C(O)), 46.9 (CH2–N–morpholine), 66.5 (CH2–O–morpho-
line), 66.6 (CH2–O–morpholine), 73.2 (CH2CHvCH2), 117.8
(CH2CHvCH2), 118.4 (C-1), 120.9 (C-5), 125.2 (C-6), 134.0
(CH2CHvCH2), 141.1 (C-4), 145.4 (C-3), 156.2 (C-2), 164.9
(CvO), 199.4 (CvO); MS (ES+) m/z = 320.1 [M + H]+;
HRMS calcd for C17H22NO5 [M + H]+ 320.1492, found
320.1493.
8-(Allyloxy)-7-methyl-2-morpholino-4H-chromen-4-one (24).
To
a solution of 1-(2-hydroxy-3-allyloxy-4-methylphenyl)-
3-morpholinopropane-1,3-dione (0.497 g, 1.56 mmol) in DCM
(15 mL) at 0 °C was added dropwise trifluoromethanesulfonic
anhydride (0.65 mL, 3.89 mmol). The reaction mixture was
warmed to room temperature and stirred for 7 h. MeOH (10 mL)
was added to the reaction mixture which was stirred for 1 h. The
solvent was removed in vacuo and sodium bicarbonate solution
(30 mL) was added to the residue, which was extracted into
DCM. The combined organic layers were dried (Na2SO4) and
concentrated in vacuo. The crude product was purified by
medium pressure column chromatography (EtOAc–MeOH
95 : 5) to give the title compound as an off-white solid (0.238 g,
51%): Rf = 0.38 (EtOAc–MeOH 95 : 5); mp: 123–125 °C;
IR (cm−1) 2979, 2942, 2866, 2362, 1646, 1608, 1558, 1397,
1236; λmax (EtOH)/nm 304, 236, 225; 1H NMR (500 MHz,
CDCl3) δ 2.39 (3H, s, CH3), 3.51–3.53 (4H, m, CH2–morpho-
line) 3.82–3.84 (4H, m, CH2–morpholine), 4.50 (2H, d, J =
5.6 Hz, CH2–CHvCH2), 5.29 (1H, dd, J = 1.3 and 10.4 Hz,
CH2–CHvCH2cis), 5.41 (1H, dd, J = 1.3 and 17.2 Hz,
CH2–CHvCH2trans), 5.47 (1H, s, H-3), 6.03 (1H, ddt, J = 5.6,
10.4 and 17.2 Hz, CH2–CHvCH2), 7.15 (1H, d, J = 8.3 Hz,
H–Ar), 7.79 (1H, d, J = 8.3 Hz, H–Ar); 13C NMR (125 MHz,
CDCl3) δ 16.6 (CH3), 44.9 (CH2–N–morpholine), 66.1 (CH2–
O–morpholine), 74.5 (CH2CHvCH2), 87.3 (C-3), 118.2
(CH2CHvCH2), 120.3 (C-7), 122.6 (C-5), 126.9 (C-6), 133.6
(CH2CHvCH2), 136.4 (C-10), 144.5 (C-9), 147.6 (C-8), 162.2
(C-2), 177.9 (C-4); MS (ES+) m/z = 302.0 [M + H]+; HRMS
calcd for C17H20NO4 [M + H]+ 302.1387, found 302.1390.
1-(3-(Allyloxy)-2-hydroxy-4-methylphenyl)-3-morpholinopropane-
1,3-dione (23). To a solution of tetrabutylammonium iodide
(0.257 g, 0.70 mmol) in DCM (2 mL) at −78 °C was added tita-
nium(IV) chloride (1 M in DCM, 0.70 mL, 0.70 mmol) dropwise
over 30 min, and the mixture was stirred for an additional
10 min. 1-(2,3-Bis(allyloxy)-4-methylphenyl)-3-morpholinopro-
pane-1,3-dione (0.119 g, 0.33 mmol) in DCM (2 mL) was added
dropwise to give a dark brown solution, which was stirred for
50 min at −78 °C and then allowed to warm to 0 °C over 1 h.
The mixture was poured into a saturated aqueous solution of
Rochelle’s salt (10 mL) and extracted into DCM (3 × 10 mL).
The combined organic layers were dried (MgSO4) and concen-
trated in vacuo. The crude product was purified by medium
pressure column chromatography (DCM–MeOH 95 : 5) to give
the title compound as a brown oil (0.105 g, 99%): Rf = 0.43
(DCM–MeOH 95 : 5); IR (cm−1) 2965, 2924, 2859, 2358, 1628,
1413, 1337, 1226; λmax (EtOH)/nm 272, 338; 1H NMR
(500 MHz, CDCl3) δ 2.26 (3H, s, CH3), 3.46 (2H, t, J = 4.8 Hz,
CH2–morpholine), 3.60–3.64 (6H, m, CH2–morpholine),
4.05 (2H, s, C(O)CH2C(O)), 4.51 (2H, d, J = 5.9 Hz,
8-Hydroxy-7-methyl-2-morpholino-4H-chromen-4-one (25).
To a mixture of 2-morpholin-4-yl-7-methyl-8-allyloxychromen-
4-one (30 mg, 0.10 mmol) in degassed ethanol (4 mL) was
added RhCl(PPh3)3 (6.4 mg, 0.007 mmol) and DABCO
(1.1 mg, 0.010 mmol). The mixture was heated at reflux for 2 h,
filtered through a pad of celite and the solvent was removed
in vacuo. The crude product was purified by medium pressure
column chromatography (EtOAc–MeOH 95 : 5) to give the title
compound as a white solid (0.022 g, 85%): Rf = 0.19 (EtOAc–
MeOH 95 : 5); mp: 296 °C decomp.; IR (cm−1) 2972, 2916,
2857, 1610, 1550, 1423, 1403, 1349; λmax (EtOH)/nm 303, 239;
1H NMR (500 MHz, DMSO-d6) δ 2.29 (3H, s, CH3), 3.57 (4H,
t, J = 4.9 Hz, CH2–morpholine), 3.73 (4H, t, J = 4.9 Hz, CH2–
morpholine), 5.44 (1H, s, H-3), 7.11 (1H, d, J = 7.9 Hz, H–Ar),
7.30 (1H, d, J = 7.9 Hz, H–Ar), 9.38 (1H, s, OH); 13C NMR
This journal is © The Royal Society of Chemistry 2012
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View Article Online
(125 MHz, DMSO-d6) δ 16.3 (CH3), 44.5 (CH2–N–morpholine),
65.4 (CH2–O–morpholine), 86.0 (C-3), 114.2 (C-7), 121.6
(C-5), 126.2 (C-6), 129.4 (C-8), 142.5 (C-9), 143.0 (C-10),
162.1 (C-2), 175.6 (C-4); MS (ES+) m/z = 262.0 [M + H]+;
HRMS calcd for C14H16NO4 [M + H]+ 262.1074, found
262.1077.
139.5 (C–Ar), 140.4 (C–Ar), 142.2 (C–Ar), 151.3 (C–Ar), 162.3
(C-2), 177.4 (C-4); MS (ES+) m/z 428.3 [M + H]+; HRMS calcd
for C26H22NO3S [M + H]+ 428.1315, found 428.1313.
Acknowledgements
We would like to thank Andrew Blythe-Dickens for the scale-up
of the synthesis described in Scheme 1, as part of his MChem
lab placement. The biochemical screening expertise of Marcus
Peacock, Nahida Parveen, William Deacon and the AstraZeneca
Oncology iMed biochemical screening team is appreciatively
recognised. The use of the EPSRC Mass Spectrometry Service
at the University of Wales (Swansea) and financial support from
Cancer Research UK are also gratefully acknowledged.
7-Methyl-2-morpholino-4-oxo-4H-chromen-8-yl trifluoro-
methanesulfonate (26). 8-Hydroxy-7-methyl-2-morpholino-4H-
chromen-4-one (0.140 g, 0.54 mmol), N-phenyl-bis(trifluoro-
methanesulfonimide) (0.383 g, 1.07 mmol) and caesium carbon-
ate (0.245 g, 0.75 mmol) were suspended in THF (15 mL). The
mixture was heated under microwave irradiation at 100 °C for
20 min. The reaction mixture was diluted with EtOAc (50 mL)
and washed with brine (50 mL) and water (50 mL). The com-
bined organic layers were dried (Na2SO4) and concentrated
in vacuo. The crude product was purified by medium pressure
column chromatography (EtOAc–MeOH 95 : 5) to give the title
compound as a white solid (0.190 g, 90%): Rf = 0.39 (EtOAc–
MeOH 95 : 5); mp: 193–195 °C; IR (cm−1) 2869, 2362, 2161,
1610, 1595, 1552, 1400, 1361; λmax (EtOH)/nm 311, 215;
1H NMR (500 MHz, CDCl3) δ 2.47 (3H, s, CH3), 3.56–3.58
(4H, m, CH2–morpholine), 3.82–3.84 (4H, m, CH2–morpho-
line), 5.49 (1H, s, H-3), 7.26 (1H, d, J = 8.0 Hz, H–Ar), 8.04
(1H, d, J = 8.0 Hz, H–Ar); 13C NMR (125 MHz, CDCl3) δ 16.7
(CH3), 45.3 (CH2–N–morpholine), 66.1 (CH2–O–morpholine),
87.6 (C-3), 118.6 (1C, q, J = 318 Hz, OSO2CF3), 123.2 (C-5),
125.0 (C-6), 127.4 (C-7), 134.9 (C-9), 135.7 (C-8), 146.3
(C-10), 162.3 (C-2), 175.6 (C-4); MS (ES+) m/z 394.0
[M + H]+; HRMS calcd for C15H15F3NO6S [M + H]+ 394.0567,
found 394.0569.
Notes and references
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to a degassed solution of 7-methyl-2-morpholino-4-oxo-4H-
chromen-8-yl trifluoromethanesulfonate (0.216 g, 0.55 mmol),
dibenzo[b,d]thiophen-4-ylboronic acid (0.250 g, 1.1 mmol) in
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irradiation at 150 °C for 50 min. The reaction mixture was
diluted with EtOAc (50 mL) and washed with brine (50 mL) and
water (50 mL). The combined organic layers were dried
(Na2SO4) and concentrated in vacuo. The crude product was
purified by medium pressure column chromatography (EtOAc–
MeOH 95 : 5) to yield the title compound as a white solid
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(C–Ar), 122.0 (C–Ar), 123.0 (C–Ar), 124.8 (C–Ar), 124.9
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