Diversity-oriented synthesis of furo[3,2-f]chromanes with antimycobacterial activity

Article abstract of DOI:10.1016/j.ejmech.2009.01.017

We previously reported the synthesis and the antimycobacterial activity of 4-(7,7-dimethyl-7H-furo[3,2-f]chromen-2-yl)pyridine. From this result, we sought to design simple synthetic accesses to related structures allowing the preparation of a diverse set

Full text of DOI:10.1016/j.ejmech.2009.01.017

European Journal of Medicinal Chemistry 44 (2009) 2497–2505
Contents lists available at ScienceDirect
European Journal of Medicinal Chemistry
journal homepage: http://www.elsevier.com/locate/ejmech
Original article
Diversity-oriented synthesis of furo[3,2-f]chromanes with
antimycobacterial activity
Luke Alvey a, Soizic Prado b, Brigitte Saint-Joanis c, Sylvie Michel d, Michel Koch d,
,
Stewart T. Cole c, François Tillequin d, Yves L. Janin a
*
a Institut Pasteur, URA 2128 CNRS-Institut Pasteur, 28 rue du Dr. Roux, 75724 Paris Cedex 15, France
b Laboratoire de Chimie et Biochimie des Substances Naturelles, UMR 5154 CNRS/MNHN, Muse´um National d’Histoire Naturelle, 57 rue Cuvier, CP54, 75005 Paris, France
c Unite´ de Ge´ne´tique Mole´culaire Bacte´rienne, Institut Pasteur, 28 rue du Dr. Roux, 75724 Paris Cedex 15, France
d Laboratoire de Pharmacognosie de l’Universite´ Paris Descartes, UMR/CNRS 8638, Faculte´ des Sciences Pharmaceutiques et Biologiques, 4 avenue de l’Observatoire,
75006 Paris, France
a r t i c l e i n f o
a b s t r a c t
Article history:
We previously reported the synthesis and the antimycobacterial activity of 4-(7,7-dimethyl-7H-furo[3,2-
f]chromen-2-yl)pyridine. From this result, we sought to design simple synthetic accesses to related
structures allowing the preparation of a diverse set of analogues. Two approaches were investigated.
From 3-(2-bromo-7,7-dimethyl-8,9-dihydro-7H-furo[3,2-f]chromen-1-yl)propyl acetate, we prepared 2-
arylated derivatives via Suzuki–Miyaura reactions between this bromine-bearing compound and various
arylboronates. Moreover, and even more simple, we prepared the ((6-hydroxy-2,2,7,8-tetramethylchro-
man-5-yl)methyl)triphenylphosphonium salt via a selective bromination of 2,2,5,7,8-pentamethylchro-
man-6-ol. From this salt, a two stage Wittig reaction with an array of activated acids allowed the quick
preparation of many analogues. The biological evaluation of the effect of these compounds on the growth
of Mycobacterium bovis as well as Mycobacterium tuberculosis pointed out a fourfold improvement of the
antimycobacterial properties for one of the compounds made. However, the many analogues which
Received 16 August 2008
Received in revised form
1 December 2008
Accepted 16 January 2009
Available online 29 January 2009
Keywords:
Antimycobacterial
Tuberculosis
Chromanes
Benzofuranes
inhibited the growth of M. tuberculosis in the 0.6–5
m
g/mL range turned out to be also cytotoxic on VERO
cells growth at the same concentration range.
Ó 2009 Elsevier Masson SAS. All rights reserved.
As described in a preceding paper [1], in the course of our
researches [2–5] on the synthesis of analogues of the specific
antimycobacterial the chromane-bearing compound 1 [6], we
have prepared the furo[3,2-f]chromene derivatives 2a,b which
displayed better inhibition activity on Mycobacterium tuberculosis
growth than the initial hit. Our first syntheses of analogues of
compounds 2a,b allowed the determination of some of the
structure–activity relationships and confirmed the potential
interest of this new series [1]. However, it became apparent that
simpler synthetic access allowing the quick preparation of an
array of analogues featuring a diverse set of substituents would
have been useful for a full exploration of the structure–activity
relationships of these series. Inherent to this aim was the design
of synthetic pathways in which the variable substituents are
introduced in the final steps of the synthesis, much preferably the
last one. We wish to report here two original approaches which
are using compound 3 or the commercially available chromane 4
as starting material for the preparation of diversity-oriented
analogues of compounds 2a,b (Fig. 1).
In the first approach, we reduced the chromene ring of the
readily available compound 3 [1], using hydrogen and palladium
over charcoal, to obtain compound 5. The other pyran ring could
then selectively opened in boiling acetic acid containing hydrogen
chloride. This gave an access to the furo[3,2-f]chromane derivative
6. The following selective halogenation of its carbon 2 was possible
using N-bromosuccinimide and provided an access to the key
precursor 7. The Suzuki–Miyaura aryl–aryl coupling reaction of the
hindered brominated compound 7 and 4- or 3-pyridylboronic
derivatives was then investigated. After few trials, the rewarding
use of the reported [1,10-bis(diphenylphosphino)ferrocene]
dichloropalladium as a precatalyst and cesium carbonate as a base
in a water/dioxane solution [7, 8] allowed the preparation, in
acceptable 60 and 55% yields, of the analogues 8a,b. The corre-
sponding pyridyl-bearing alcohols 9a,b were then obtained by the
methanolysis of their acetyl moiety (Scheme 1).
* Corresponding author. Institut Pasteur, Laboratoire de chimie organique, URA
2128 CNRS-Institut Pasteur, 28 rue du Dr. Roux, 75724 Paris Cedex 15, France. Fax:
þ33 (0) 1 45 68 84 04.
In a second approach, we made good use of a synthetic
scheme initially reported for the preparation of benzofuranes [9]
E-mail address: yves.janin@pasteur.fr (Y.L. Janin).
0223-5234/$ – see front matter Ó 2009 Elsevier Masson SAS. All rights reserved.
doi:10.1016/j.ejmech.2009.01.017

2498
L. Alvey et al. / European Journal of Medicinal Chemistry 44 (2009) 2497–2505
Fig. 1.
and further developed for the preparation of furo[3,2-f]chro-
manes [10]. Starting from the commercially available chromanol
4, a regioselective bromination [11,12] of its C5 methyl gave
compound 10. This was followed by the preparation of the
phosphonium salt 11. This salt could then react with an array of
activated acids to give the 2-arylated furo[3,2-f]chromanes 13a–i
via the corresponding esters 12 in a two stage process [9,13]. As
we extended this route, various procedures, fully described in
the experimental part, were used. In the first stage, which led to
the intermediate esters 12, acyl chlorides, as well as dicyclo-
hexylcarbodiimide-activated acids were successfully reacted
with the phosphonium salt 11. The cyclization of these inter-
mediates was then achieved by the addition of triethylamine to
the medium and extensive heating. It became apparent that
a stock solution of the phosphonium 11 in dichloromethane
could be used and that the rather long heating time required for
cyclization of the intermediate esters could be undertaken in this
solvent at temperature as high as 65 ꢀC, provided it was done in
a sealed tube (Scheme 2).
The reaction yields for the preparation of compounds 13a–j were
observed to vary between 5.5 and 90% depending on the acid
considered and the coupling method used. We did not try to optimize
the fairly low 5.5% yield of compound 13f, which is likely to be due to
the instability of the intermediate malonyl ester. By using a three-
stage process, we also prepared the amide-bearing compound 14a–c
from compound 11, succinic anhydride, various secondary amines
and DCC. Further refinement of this strategy led us to isolate the
phosphonium salt 11 which, contrary to what has been reported [10],
turns out to be perfectly stable; if made from compound 4 in a one pot
procedure using N-bromosuccinimide. This is probably due tothe fact
Scheme 2. (i) Br2 cyclohexane. (ii) PPh3, CH2Cl2 or cyclohexane. (iii) RCOCl or RCOOH,
DCC; NEt3. (iv) NEt3, heat.
that we avoided the use of bromine and thus obtained compound 10
free of traces of hydrogen bromide. Moreover, we could replace the
rather long heating time by using a microwave oven. This allowed the
subsequent synthesis of analogues 15a–d from the corresponding
acylchlorides or the acids using a much simplified procedure
involvingDCC and hydroxybenzotriazole inacetonitrile(Scheme 3). A
similar use of microwave heating has actually been reported very
recently for the synthesis of benzofuranes from (2-hydroxybenzyl)-
triphenylphosphonium salt and various acids activated by tri-
chlorotriazine [14].
As shown in Scheme 4, some subsequent modifications were
made. The oxidation of compound 13a with cerium ammonium
nitrate turned out to lead to 74% of the ketone 16 whereas its
oxidation with 3-chloroperbenzoic acid gave the N-oxide derivative
17. A nucleophilic substitution reaction with the chloropyridine-
bearing derivative 13d gave the far more soluble diaminated
analogue 18. Also from this chloropyridine-bearing derivative 13d,
a palladium-catalysed substitution reaction with zinc cyanide [15]
led to the nitrile-bearing analogue 19. The first element of struc-
ture–activity relationship obtained led us to prepare a few other
derivatives from compound 19. For instance its nitrile moiety was
transformed in a tetrazole via a (slow) cycloaddition reaction with
hydrazoic acid generated in situ to give compound 20. Moreover,
Scheme 1. (i) HCOOH, NH3, Pd/C ethanol reflux. (ii) AcOH, HCl reflux. (iii) NBS, EtOH.
(iv) ArB(OH)2, Pd dppf, dioxane–water, Cs2CO3, 80 ꢀC. (v) MeONa/MeOH.
Scheme 3. (i) Succinic anhydride, amine, CH2Cl2, then DCC; 11, NEt3, heat. (ii) RCOOH,
DCC, HOBt, (or RCOCl) NEt3, MeCN, 120 ꢀC (microwave).

L. Alvey et al. / European Journal of Medicinal Chemistry 44 (2009) 2497–2505
2499
Table 1
In vitro biological assays.
a
a
Compound
MIC95
MIC95
IC50
M. bovis
M. tuberculosis
(VERO cells)
Isoniazid
0.4
0.25
10
10
2.5
5
250
10
>10
5
5
5
5
>500
N.D.
100
8.7
a
-Tocopherol
N.D.
N.D.
6.2
1
2a
2b
3
4
7
8a
8b
6.2
12.8
N.D.
N.D.
N.D.
14.9
17.5
>25
>25
N.D.
N.D.
5.1
N.D.
>100
N.D.
N.D.
6.4
N.D.
N.D.
N.D.
N.D.
N.D.
>100
7.3
N.D.
N.D.
50
3.1
12.5
12.5
6.2
3.1
>100
3.1
>100
>100
N.D.
>100
6.2
9a
9b
13a
13b
13c
13d
13e
13f
13g
13h
13i
13j
14a
14b
14c
15a
15b
15c
15d
16
5
10
2.5
>10
25
>10
100
3
10
>10
10
Scheme 4. (i) (NH4)2Ce(NO3)6, MeCN, 25 ꢀC. (ii) mCpBA, CH2Cl2, 25 ꢀC. (iii)
Amine, reflux. (iv) ZnCN, PdCl2dppf, DMA, 120 ꢀC. (v) NaN3, NEt3, HCl, toluene,
80 ꢀC. (vi) tBuOK, MeOH, 25 ꢀC.
25
N.D.
>100
N.D.
N.D.
6.2
the imidoester 21 was easily prepared via the addition of meth-
anolate on the nitrile function of compound 19 [16].
>10
10
5
1. Biological results and discussion
3.1
5
>100
>100
N.D.
12.5
6.2
6.2
12.5
>10
5
>100
ND
N.D.
5.6
The antimycobacterial activity was screened most often on
Mycobacterium bovis BCG as well as on the virulent strain M.
tuberculosis H37Rv, using the new Microdilution Resazurin
17
18
3
1.6
Assay (MRA) [17]. The minimal inhibitory concentration (MIC95
)
19
20
21
ND
25
6.2
>10
10
0.6
N.D.
N.D.
3.6
is defined as the amount of compound required for >95% inhi-
bition of bacterial growth is provided in microgram per milli-
litre. The compounds found to be the most active against
M. tuberculosis were further evaluated for their cytotoxicity on
mammalian VERO cell lines using the dimethylthiazolyldiphenyl
tetrazolium (MTT)-based assay. All these results are summarized
in Table 1.
Even if the solubility remains an issue with many compounds
of this series, some of the antimycobacterial activity obtained
point out interesting structure–activity relationships. For
instance, when compared to compound 2a, a fourfold improve-
ment of antimycobacterial effect was seen for compound 21.
However, the cytotoxicity measurement of some of the most
active compounds dampened very much these encouraging
results. Unfortunately, the most effective antimycobacterials
(compounds 2a,b, 8a, 13h, 15b, 17, 18 and 21) were also cytotoxic
at the same concentration range. Moreover, an SOS-chromotest
pointed out that, amongst these analogues, compound 18 is also
mutagenic. As a selectivity of action on the mycobacteria genus
had been observed [6] for compound 1, the inhibition of the
growth of Staphylococcus aureus, Escherichia coli and Candida
tropicalis by these analogues was also measured. None were
found active on Gram-negative E. coli, however the cytotoxic
compounds (2a,b, 8a, 13h, 15b, 17, 18 and 21) had an effect on the
ND: not determined.
a
All the values provided are in mg/mL.
lipophilic antioxidant 2,6-bistertbutylpcresol (BHT) was devoid
of antimycobacterial activity. In conclusion, from the structure of
the remarkably selective antimycobacterial compound 1 repor-
ted in 2006 [6], our research program on the design of synthetic
access to structural analogues proved quite fruitful from the
organic chemistry point of view [1–4]. However, the anti-
mycobacterial agents previously made, although sometime of
interest, turned out to be cytotoxic as well [3] or were not really
better than the starting point [4]. The present investigation in
chemistry provides two original synthetic accesses to 7H-
furo[3,2-f]chromene analogues of 2a,b. From our work on the
chemistry of formylbenzoquinone [1], two successive cycload-
ditions led to compound 5. This was then transformed into the
brominated precursor 7 which allowed for a quick access to
chemically diverse compounds using the Suzuki–Miyaura palla-
dium-catalysed aryl–aryl coupling reaction. Further investiga-
tions led us to the use of the readily available phosphonium salt
11 featuring a chromane ring system. This provided a single step
access to many derivatives featuring the 7H-furo[3,2-f]chromen
ring system with a multitude of possible substituents on carbon
C-2 as well as two methyls on the central ring. Unfortunately, the
many analogues made which inhibit the growth of M. tubercu-
losis in the low microgram per millilitre range are also cytotoxic
at this concentration. Interestingly, the lipophilic thiophene-
bearing compound 15c and to a lesser extent compound 15d
seem to have a selective action on M. tuberculosis (assays of these
two compounds on Mycobacterium. smegmatis growth also
Gram-positive S. aureus growth with MIC90 between 5 and 18
mg/
mL. Moreover, compound 18, the only mutagenic one, had
a measurable diameter of inhibition on the growth of C. albicans.
Interestingly, the structurally related antioxidant
well as the smaller chromanol 4 inhibited M. tuberculosis growth.
Concerning -tocopherol, this antimycobacterial effect had
a-tocopherol as
a
actually been previously reported [18–20]. In any case, this
inhibition suggests an antioxidant-based mechanism of action
for these antibacterials as they share a common ‘‘oxy’’-chromane
ring system. However, this is very much a hypothesis as the fairly
showed a lack of effects even at a 100
These facts, especially the cytotoxicity observed, will have to be
mg/mL concentration).

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L. Alvey et al. / European Journal of Medicinal Chemistry 44 (2009) 2497–2505
taken into account in any design of further analogues of
compound 1 or 2a,b.
cells were seeded in 96-well microtitration plates at a density of
105 cells/mL, which were further incubated for 24 h at 37 ꢀC under
5% CO2 in air before each assay. Various concentrations of solutions
of compounds in 1% DMSO were added and then incubated for 48 h
2. Experimental part
as described above. At the end of this, 20 mL of dimethylth-
2.1. Chemistry
iazolyldiphenyl tetrazolium bromide solution (MTT, Sigma) (5 mg/
mL) was added to each well and further incubated for 4 h at 37 ꢀC to
allow the formation of formazan. The crystals of formazan were
A Biotage Initiator 2 microwave oven was used for reactions
requiring microwave irradiations. The 1H NMR and 13C NMR
spectra were recorded on a Bruker Avance 400 spectrometer at
400 MHz and 100 MHz, respectively. Unless otherwise noted,
then dissolved with 100
mL of a freshly prepared solution of sodium
dodecyl sulfate (SDS) 10% (15 mL) and HCl 1 N (150
mL). The optical
density of each well was measured at 595 nm using a multi-well
plate reader. The 50% inhibition concentration was then deter-
mined by curve fitting.
CDCl3 was the solvent used. Shifts (d) are given in ppm with
respect to the TMS signal and coupling constants (J) are given in
Hertz. Column chromatography was performed either with Merck
silica gel 60 (0.035–0.070 mm) or neutral alumina containing
a suitable proportion of water, using a solvent pump operating at
pressure between 2 and 7 bar (25–50 mL/min) and an automated
collecting system driven by a UV detector set to 254 nm unless
stated otherwise (i.e. if ethyl acetate was used then it would be set
to 280 nm). Sample deposition was always carried out by
absorption of the mixture to be purified on a small amount of the
solid phase followed by its deposition on the top of the column.
The low resolution mass spectra were obtained on an Agilent 1100
serie LC/MSD system using an atmospheric electrospray ionisation
system and the high resolution mass spectroscopy spectra (HRMS)
were obtained using a Waters Micromass Q-Tof with an electro-
spray ion source.
2.2.4. MIC determination for bacteria
Pre-cultures of the tested microorganisms E. coli or S. aureus
were made by inoculating 10 mL of Luria-Bertani (LB) and incu-
bating for 24 h. A culture suspension was made by 1/1000 dilution
from preculture and seeded in 96-well microtitration plates. One
microliter of twofold serial dilutions of each drug was prepared in
100 m
L of LB. The plates were incubated at 37 ꢀC. After 24 h, the
optical density of each well was measured at 595 nm using a mul-
tiplate reader. The 90% inhibition concentrations for the most active
compounds were determined by curve fitting. Tetracycline was
used as positive control.
2.2.5. Antifungal activity
Activities of the more active compounds were evaluated on the
growth of C. tropicalis using the standardized filter paper disk
(6 mm non-impregnated disk; Antibiotica assay discs, Grade 2668
Schleider and Schuell) diffusion method according to the Kirby–
Bauer method [21]. Briefly, a suspension of C. tropicalis was spread
on solid Sabouraud media plates (20 mL). Filter paper discs were
2.2. Biology
2.2.1. Strains
Reference strains of E. coli (CIP188631), S. aureus (ATCC6538),
C. tropicalis (ATCC66029), M. smegmatis mc2155, M. tuberculosis
H37Rv (Institut Pasteur, Paris, France), M. bovis BCG (Pasteur),
impregnated with 10 mL of serial dilutions in dimethylsulfoxide
E. coli, PQ37 (Fꢁ thr leu his-4 pyrD thi galE galK lac
D
U169
(DMSO, Sigma) of the compounds and placed onto the solid media
plates. The diameter of inhibition was measured after 24 h of
incubation at 30 ꢀC. Itraconazole was used as positive control.
srl300TTn10 rpoB rpsL uvrA rfa trpTMucþ sfiATMud (Ap, lac) cts)
were obtained from the Collection of the Institut Pasteur.
All the biological assays were made in duplicate in two inde-
pendent experiences, for this reason no standard deviation could be
calculated.
2.2.6. Genotoxicity assay: SOS-chromotest
The capacity of the drugs to induce DNA damage is moni-
tored with the SOS-chromotest [22]. This test is based on
a genetically engineered E. coli strain, PQ37 licensed from the
Institut Pasteur, which measures the primary response of a cell
to genotoxic damage. This strain harbours the lacZ gene under
the control of sfiA, a gene involved in the SOS response. DNA
damage results in the activation of the SOS system which in turn
2.2.2. MIC determinations for mycobacteria
MICs were determined using the new Microdilution Resazurin
Assay (MRA) [17]. Resazurin salt powder (Sigma) was prepared at
0.01% (wt/vol) in distilled water, sterilized by filtration through
a 0.22 m
m membrane and stored at 4 ꢀC for a week. Drug stock
solutions were prepared in dimethylsulfoxide (DMSO) at
a concentration of 50 mg/mL and frozen until used. The inocula
were prepared from M. tuberculosis H37Rv or from M. bovis BCG
strains grown in Dubos medium supplemented with 10% ADC
enrichment (Difco). One microliter of twofold serial dilutions of
induces the transcription and synthesis of
b
-galactosidase. This
enzyme is detected by
substrate X-gal.
a chromogenic reaction with the
each drug were prepared in 100
well plates at concentrations from 500
controls containing DMSO and isoniazid (from 1
were also included. The plates were covered, sealed and incubated
at 37 ꢀC. After 6 days (or 8 for M. bovis), 30
L of resazurin solution
was added to each well and plates were allowed to incubate at
37 ꢀC for an additional 24 h. A change from blue to pink indicates
reduction of resazurin and therefore bacterial growth. The MIC was
defined as the lowest drug concentration that prevented this colour
change.
m
L of Dubos medium directly in 96-
g/mL to 0.9 g/mL. Growth
g/mL to 1 ng/mL)
2.3. 3,3-Dimethyl-2,3,9,10,11,11a-hexahydro-1H,7aH-4,7,8-trioxa-
benzo[c]fluorene (5)
m
m
m
Compound 3 (2.89 g, 0.011 mol) was dissolved in ethanol
(300 mL), ammonium formate (1.41 g, 0.022 mol) and 10% palla-
dium over charcoal (0.59 g, 0.5 mmol) were then added. This
suspension was heated to reflux for 40 min before filtering it. The
concentrated filtrate yielded compound 5 as an oil, almost invisible
on TLC using an UV lamp, which was used in the next step without
further purification. 1H NMR (CDCl3): 1.31 (s, 3H), 1.35 (s, 3H), 1.64
(m, 3H), 1.79 (m, 2H), 2.11 (m, 1H), 2.69 (t, 2H, J ¼ 6.7), 3.11 (s, 1H),
3.87 (m, 2H), 5.84 (d, 1H, J ¼ 6.3), 6.58 (d, 1H, J ¼ 8.5), 6.63 (d, 1H,
J ¼ 8.5). 13C NMR (CDCl3): 20.3, 21.3, 26.3, 27.3, 27.8, 32.7, 38.0, 61.6,
73.7, 104.9, 109.0, 116.5, 118.3, 129.3, 148.5, 150.4.
m
2.2.3. Cytotoxicity evaluation
VERO cell lines were maintained in DMEM supplemented with
5% Foetal calf serum (FCS), at 37 ꢀC in air with 5% CO2. Proliferating

L. Alvey et al. / European Journal of Medicinal Chemistry 44 (2009) 2497–2505
2501
2.4. 3-(7,7-Dimethyl-8,9-dihydro-7H-furo[3,2-f]chromen-1-yl)-
propyl acetate (6)
4.19 (t, 2H, J ¼ 6.1), 6.82 (d, 1H, J ¼ 8.8), 7.26 (d, 1H, J ¼ 8.8), 7.44 (m,
1H), 8.06 (m, 1H), 8.62 (m, 1H), 9.00 (m, 1H). 13C NMR (CDCl3): 19.9,
20.8, 21.7, 26.6, 30.7, 32.5, 63.5, 73.3, 110.2, 112.9, 116.3, 118.2, 123.7,
127.2, 127.8, 134.5, 147.4, 148.3, 148.5, 149.1, 149.7, 170.9.
The crude compound 5 was refluxed in acetic acid (100 mL)
containing 2 N hydrochloric acid (5 mL) for 2 h. The resulting solu-
tion was concentrated to dryness and diluted in dichloromethane.
The organic phase was washed with saturated solution of sodium
hydrogenocarbonate then water, dried over sodium sulfate and
concentrated to dryness. The residue was purified by a chromatog-
raphy over silica gel (cyclohexane/ethyl acetate 6:1) to yield
compound 6 as a solid (2.69 g, 79% from compound 3). m.p. ¼ 82 ꢀC.
HRMS (ES) calc. for: C18H22O4Na 325.1416; found: 325.1473. 1H NMR
(CDCl3): 1.37 (s, 6H), 1.88 (t, 2H, J ¼ 6.7), 2.04 (m, 2H), 2.09 (s, 3H),
2.86 (m, 2H), 3.10 (m, 2H), 4.21 (t, 2H, J ¼ 6.7), 6.7 (d,1H, J ¼ 8.8), 7.20
(d, 1H, J ¼ 8.8), 7.35 (s, 1H). 13C NMR (CDCl3): 20.6, 21.3, 22.2, 27.0,
29.5, 32.9, 64.2, 73.6, 110.6, 113.2, 115.5, 120.8, 126.2, 142.2, 149.6,
150.5, 171.4.
2.7. Preparation of compounds 9a,b
Esters 8a,b (0.15 g, 0.39 mmol) were dissolved in 1 N sodium
methanolate in methanol solution (10 mL) and stirred overnight.
The solution was partially concentrated, dispersed in dichloro-
methane and the organic phase was washed with water; the
organic phase was dried over sodium sulfate and concentrated to
dryness to yield pure compounds 9a,b as described below. Nota
NMR measurement had to be made in DMSO-d6 as in CDCl3, the
occurrence of two unequal sets of signals was observed.
2.7.1. 3-(7,7-Dimethyl-2-(pyridin-4-yl)-8,9-dihydro-7H-
furo[3,2-f]chromen-1-yl)propan-1-ol (9a)
2.5. 3-(2-Bromo-7,7-dimethyl-8,9-dihydro-7H-furo[3,2-f]-
chromen-1-yl)propyl acetate (7)
Obtained in a 45% yield as solid after a recrystallisation in
a toluene/cyclohexane mixture. m.p. ¼142 ꢀC. HRMS (ES) calc. for:
C21H24NO3 338.1756; found: 338.1731. 1H NMR (DMSO-d6): 1.30 (s,
6H), 1.86 (m, 4H), 3.06 (m, 2H), 3.14 (m, 2H), 3.59 (m, 2H), 4.68 (t
(ex), 1H, J ¼ 5.1), 6.78 (d, 1H, J ¼ 8.8), 7.32 (d, 1H, J ¼ 8.8), 7.72 (m,
2H), 8.68 (m, 2H). 13C NMR (DMSO-d6): 20.0, 22.1, 27.1, 32.6, 35.0,
61.1, 74.0, 110.9, 114.5, 117.5, 120.8, 122.6, 128.0, 138.3, 148.2, 149.1,
150.1, 151.1.
Compound 6 (0.11 g, 0.36 mmol) was dissolved in ethanol
(20 mL) and N-bromosuccinimide (0.071 g, 0.4 mmol) was added.
The solution was stirred for 40 min and concentrated to dryness.
The residue was purified by a chromatography over silica gel
(cyclohexane/ethyl acetate 6:1) to yield compound 6 as wax (0.12 g,
86%, traces of a bis-brominated product were observed). HRMS (ES)
79
calc. for: C18
H
BrO4 381.0702; found: 381.1157. 1H NMR (CDCl3):
21
1.37 (s, 6H), 1.88 (t, 2H, J ¼ 6.7), 1.98 (m, 2H), 2.08 (s, 3H), 2.81 (m,
2H), 3.06 (t, 2H, J ¼ 6.7), 4.18 (t, 2H, J ¼ 6.4), 6.73 (d, 1H, J ¼ 8.9), 7.17
(d, 1H, J ¼ 8.9). 13C NMR (CDCl3): 20.2, 21.3, 22.4, 26.9, 30.0, 32.7,
64.0, 73.8, 110.3, 112.3, 115.4, 119.3, 126.6, 127.5, 150.2, 150.2, 171.4.
2.7.2. 3-(7,7-Dimethyl-2-(pyridin-3-yl)-8,9-dihydro-7H-
furo[3,2-f]chromen-1-yl)propan-1-ol (9b)
Obtained in a 95% yield as a solid. m.p. ¼ 65 ꢀC. HRMS (ES) calc.
for: C21H24NO3 338.1756; found: 338.1764. 1H NMR (DMSO-d6):
1.30 (s, 6H), 1.86 (m, 4H), 2.99 (m, 2H), 3.16 (t, 2H, J ¼ 6.7), 3.55 (m,
2H), 4.63 (t (ex), 1H, J ¼ 5.1), 6.73 (d, 1H, J ¼ 8.8), 7.31 (d, 1H, J ¼ 8.8),
7.55 (m, 1H), 8.12 (m, 1H), 8.60 (m, 1H), 8.95 (m, 1H). 13C NMR
(DMSO-d6): 19.6, 21.6, 26.8, 32.3, 35.1, 60.7, 73.6, 110.3, 113.8, 116.1,
119.7, 124.4, 127.6, 134.3, 147.6, 148.3, 148.7, 149.3, 149.7.
2.6. Preparation of compounds 8a,b
In a 60 mL round-bottomed thick glass tube fitted with a PTFE-
faced screw-cap, compound 7 (0.2 g, 5.26 mmol), pyridine-4-
boronic acid (9.47 mmol) or pyridine-3-boronic acid 1,3-propane-
diol ester (9.47 mmol), cesium carbonate (0.68 g, 21 mmol) were
dispersed in a water (2 mL)–dioxane (5 mL) mixture. This was
degassed with slow stream of argon for 10 min before adding [1,10-
bis(diphenylphosphino)ferrocene] dichloropalladium (II) com-
plexed with dichloromethane (0.02 g, 0.26 mmol). The tube was
tightly closed and heated at 80 ꢀC for 8 h. The resulting solution was
dispersed in ethyl acetate, washed with water; the organic phase
was dried over sodium sulfate and concentrated to dryness. The
residue was purified by a chromatography over silica gel (cyclo-
hexane/ethyl acetate 3:2) to yield compounds 8a,b as described
below.
2.8. ((6-Hydroxy-2,2,7,8-tetramethylchroman-5-yl)methyl)
triphenylphosphonium bromide (11)
A
solution of this compound was prepared by reacting
compound 10 (4.6 g, 15.41 mmol; first prepared as previously
described [10]) and triphenylphosphine (4.05 g, 15.47 mmol) in
dichloromethane (9.2 mL, dried over 4 Å molecular sieves). LC/MS
monitoring of this solution pointed out its stability over time and
this was thus used as a stock solution for the preparation of some of
the compound below.
Further investigations led to the following procedure which
allows the isolation of this phosphonium salt. To a solution of
2,2,5,7,8-pentamethylchroman-6-ol (10.66 g, 0.048 mol) in toluene
(300 mL), N-bromosuccinimide (8.61 g, 0.048 mol) was added. The
solution was stirred for 45 min and triphenylphosphine (12.94 g,
0.049 mol) was added. This was stirred overnight, the resulting
suspension was heated to reflux, filtered while hot and the precip-
itate was further washed with boiling toluene (200 mL). The
resulting white powder was dried under vacuum at 60 ꢀC to yield
pure compound 11 (23.3 g, 85%). m.p. > 260 ꢀC. HRMS (ES) calc. for:
C32H34PO2 481.2296; found: 481.2310. 1H NMR (CDCl3): 1.09 (s, 6H),
1.45 (t, 2H, J ¼ 6.7), 1.97 (s, 3H), 2.01 (d, 3H, J ¼ 3.0), 2.16 (t, 2H,
J ¼ 6.7), 5.99 (d, 2H, J ¼ 13.1), 7.58 (m, 12H), 7.71 (m, 3H). 13C NMR
(CDCl3): 12.2, 13.3, 21.6, 25.8 (d, J ¼ 46), 26.5, 32.8, 72.5, 112.6 (d,
J ¼ 9), 116.2 (d, J ¼ 5), 119.0 (d, J ¼ 84),125.3, 126.6 (d, J ¼ 5), 129.8 (d,
J ¼ 12), 134.2 (d, J ¼ 10), 134.6 (d, J ¼ 3), 146.2 (d, J ¼ 3), 146.9.
2.6.1. 3-(7,7-Dimethyl-2-(pyridin-4-yl)-8,9-dihydro-7H-
furo[3,2-f]chromen-1-yl)propyl acetate (8a)
Obtained in a 60% yield as a wax, which contained traces of a bis-
brominated derivative of 7. HRMS (ES) calc. for: C23H26NO4
380.1862; found: 380.1868. 1H NMR (CDCl3): 1.39 (s, 6H), 1.91 (t, 2H,
J ¼ 6.7), 2.09 (s, 3H), 2.10 (m, 2H), 3.14 (m, 4H), 4.23 (t, 2H, J ¼ 6.1),
6.85 (d,1H, J ¼ 8.9), 7.26 (d,1H, J ¼ 8.9), 7.68 (m, 2H), 8.71 (m, 2H).13C
NMR (CDCl3): 19.9, 20.8, 21.9, 26.5, 30.3, 32.4, 63.6, 73.3,110.3,113.0,
117.3, 120.4, 120.7, 127.2, 138.8, 148.1, 149.7, 148.8, 170.8.
2.6.2. 3-(7,7-Dimethyl-2-(pyridin-3-yl)-8,9-dihydro-7H-
furo[3,2-f]chromen-1-yl)propyl acetate (8b)
Obtained in a 55% yield as a wax. HRMS (ES) calc. for: C23H26NO4
380.1862; found: 380.1884. 1H NMR (CDCl3): 1.39 (s, 6H), 1.91 (t, 2H,
J ¼ 6.7), 2.07 (s, 3H), 2.08 (m, 2H), 3.08 (m, 2H), 3.17 (t, 2H, J ¼ 6.7),

2502
L. Alvey et al. / European Journal of Medicinal Chemistry 44 (2009) 2497–2505
2.9. 3-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]-
chromen-2-yl)pyridine (13a)
2.10.4. 2-(4-Chlorobenzyl)-4,5,7,7-tetramethyl-8,9-dihydro-7H-
furo[3,2-f]chromene (13e)
This compound was obtained as a solid in a 50% yield after
A solution of 10 (0.25 g, 0.83 mmol) and triphenylphosphine
(0.22 g, 0.84 mmol) was stirred in cyclohexane (20 mL; dried over
4 Å molecular sieves) for 2 h. The solvent was removed under
vacuum at room temperature before nicotinoyl chloride hydro-
chloride (0.16 g, 0.90 mmol), triethylamine (0.38 mL, 2.7 mmol)
and toluene (20 mL; dried over 4 Å molecular sieves) were added.
The mixture was then heated at 115 ꢀC for 12 h. Upon cooling,
volatiles were removed via rotary evaporation, and the residue was
purified by a chromatography over silica gel (ethyl acetate/cyclo-
hexane 1:2). Further purification of the corresponding chromato-
graphic fraction was achieved by a second chromatography over
neutral alumina containing 1.5% water (ethyl acetate/cyclohexane
1:6) to give compound 13a as a solid (0.097 g, 38% yield).
m.p. ¼142 ꢀC. HRMS (ES) calc. for: C20H22NO2 308.1651; found:
308.1709. 1H NMR (CDCl3): 1.38 (s, 6H), 1.90 (t, 2H, J ¼ 6.8), 2.24 (s,
3H), 2.49 (s, 3H), 2.92 (t, 2H, J ¼ 6.8), 7.05 (s,1H), 7.40 (dd,1H, J ¼ 4.7,
8.0), 8.15 (td, 1H, J ¼ 1.7, 8.0), 8.55 (d, 1H, J ¼ 4.7), 9.11 (d, 1H, J ¼ 1.7).
13C NMR (CDCl3): 12.3, 12.4, 20.5, 27.2, 32.7, 74.1, 101.9, 109.1, 118.8,
123.9, 124.1, 125.0, 127.9, 132.2, 145.9, 148.30, 148.33, 149.2, 151.7.
a chromatography over silica gel (dichloromethane/cyclohexane
35
3:97). m.p. ¼ 78 ꢀC. HRMS (ES) calc. for: C22
H ClO2 355.1465;
23
found: 355.1355. 1H NMR (CDCl3): 1.37 (s, 6H), 1.85 (t, 2H, J ¼ 6.8),
2.22 (s, 3H), 2.40 (s, 3H), 2.82 (t, 2H, J ¼ 6.8), 4.08 (s, 2H), 6.27 (s,1H),
7.25 (m, 2H), 7.32 (m, 2H). 13C NMR (CDCl3): 11.7, 12.1, 20.2, 26.8,
32.5, 34.5, 73.5, 101.9, 108.4, 118.0, 121.3, 124.3, 128.6, 130.3, 132.4,
136.3, 147.4, 148.3, 155.8.
2.11. Preparation of compounds 13f–g from carboxylic acids and
dicyclohexylcarbodiimide
In a 40 mL round-bottomed thick glass tube fitted with a PTFE-
faced cap, the relevant acid (1.75 mmol) and dicyclohex-
ylcarbodiimide (1.77 mmol) were dissolved in dichloromethane
(5 mL, dried over 4 Å molecular sieves). After stirring for 30 min,
the stock dichloromethane solution of the phosphonium salt 11
(1.67 mmol) described above was added. After another 30 min of
stirring, triethylamine (0.95 mL, 4.8 mmol, dried over 4 Å molec-
ular sieves) was added and this was refluxed for 88 h before
concentrating it to dryness. The resulting paste was dispersed in
boiling cyclohexane, filtered and the filtrate concentrated to
dryness. The resulting residue was purified as described below.
2.10. Preparation of compounds 13b–e from acyl chlorides
In a 40 mL round-bottomed thick glass tube fitted with a PTFE-
faced cap, the stock dichloromethane solution of the phosphonium
salt 11 (1.67 mmol) described above, the relevant acyl chloride
(2.1 mmol) and triethylamine (0.95 mL, 4.8 mmol, dried over 4 Å
molecular sieves) were mixed in dichloromethane (10 mL, dried
over 4 Å molecular sieves). This was refluxed for 88 h and then
concentrated to dryness. The resulting residues containing
compounds 13b–d were purified accordingly as described below.
2.11.1. 2-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]-
chromen-2-yl)acetonitrile (13f)
This compound was obtained as a solid in a 5.5% yield after
a chromatography over silica gel (ethyl acetate/cyclohexane 1:6).
m.p. ¼143 ꢀC. HRMS (ES) calc. for: C17H20NO2 270.1494; found:
270.1487. 1H NMR (CDCl3): 1.36 (s, 6H), 1.86 (t, 2H, J ¼ 6.8), 2.21 (s,
3H), 2.39 (s, 3H), 2.85 (t, 2H, J ¼ 6.8), 3.91 (s, 2H), 6.65 (s, 1H). 13C
NMR (CDCl3): 12.2, 12.4, 18.6, 20.5, 27.2, 32.7, 74.0, 104.2, 109.1,
115.9, 118.6, 123.2, 124.0, 144.9, 148.2, 149.2.
2.10.1. (4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]chromen-2-
yl)methyl acetate (13b)
2.11.2. 2-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]-
chromen-2-yl)pyridine (13g)
This compound was obtained as a solid in a 80% yield after
a chromatography over silica gel (ethyl acetate/cyclohexane 1:9).
m.p. ¼ 93 ꢀC. HRMS (ES) calc. for: C18H22O4Na 325.1416; found:
325.1432. 1H NMR (CDCl3): 1.39 (s, 6H), 1.87 (t, 2H, J ¼ 6.8), 2.15 (s,
3H), 2.25 (s, 3H), 2.45 (s, 3H), 2.87 (t, 2H, J ¼ 6.8), 5.22 (s, 2H), 6.71
(s, 1H). 13C NMR (CDCl3): 12.2, 12.5, 20.5, 21.3, 27.2, 32.9, 59.3, 74.1,
106.3, 109.2, 118.8, 123.4, 124.1, 148.0, 149.2, 151.0, 171.0.
This compound was obtained as a solid in a 80% yield after
a chromatography over silica gel (ethyl acetate/cyclohexane 1:9).
m.p. ¼126 ꢀC. HRMS (ES) calc. for: C20H22NO2 308.1651; found:
308.1666. 1H NMR (CDCl3): 1.39 (s, 6H), 1.89 (t, 2H, J ¼ 6.8), 2.26 (s,
3H), 2.51 (s, 3H), 2.93 (t, 2H, J ¼ 6.8), 7.20 (m, 1H), 7.44 (s, 1H), 7.76
(m, 1H), 7.92 (d, 1H, J ¼ 7.9), 8.66 (d, 1H, J ¼ 4.6). 13C NMR (CDCl3):
12.3, 12.5, 20.4, 27.2, 32.8, 74.1, 104.0, 109.5, 118.7, 119.7, 122.6, 124.1,
125.2, 137.1, 148.3, 149.4, 150.0, 150.2, 154.3.
2.10.2. 4-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]-
chromen-2-yl)pyridine (13c)
This compound was obtained as a solid in a 80% yield after
a chromatography over silica gel (ethyl acetate/cyclohexane 1:1).
m.p. ¼159 ꢀC. HRMS (ES) calc. for: C20H22NO2 308.1651; found:
308.1637. 1H NMR (CDCl3): 1.38 (s, 6H), 1.89 (t, 2H, J ¼ 6.8), 2.25 (s,
3H), 2.48 (s, 3H), 2.91 (t, 2H, J ¼ 6.8), 7.15 (s, 1H), 7.68 (m, 2H), 8.66
(m, 2H). 13C NMR (CDCl3): 12.3, 12.4, 20.5, 27.2, 32.7, 74.1, 104.0,
109.2, 118.8, 118.9, 124.8, 124.9, 138.5, 148.4, 149.4, 150.4, 151.9.
2.11.3. 3-((4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]-
chromen-2-yl)methyl)pyridine (13h)
This compound was obtained as a solid in a 27% yield after two
successive chromatographies over silica gel (ethyl acetate/cyclo-
hexane 1:2 and then ethyl acetate/dichloromethane 1:6).
m.p. ¼ 89 ꢀC. HRMS (ES) calc. for: C21H24NO2 322.1807; found:
322.1846. 1H NMR (CDCl3): 1.35 (s, 6H), 1.84 (t, 2H, J ¼ 6.8), 2.21 (s,
3H), 2.39 (s, 3H), 2.81 (t, 2H, J ¼ 6.8), 4.11 (s, 2H), 6.29 (s, 1H), 7.27
(m, 1H), 7.64 (m, 1H), 8.54 (m, 1H), 8.63 (m, 1H). 13C NMR (CDCl3):
12.1, 12.5, 20.5, 27.2, 32.8, 32.82, 74.8, 102.5, 108.8, 118.4, 121.9,
123.9, 124.6, 133.8, 136.8, 147.8, 148.4, 148.8, 150.5, 155.4.
2.10.3. 2-Chloro-5-(4,5,7,7-tetramethyl-8,9-dihydro-7H-furo-
[3,2-f]chromen-2-yl)pyridine (13d)
This compound was obtained as a solid in a 90% yield after
a chromatography over silica gel (dichloromethane/cyclohexane
35
3:1). m.p. ¼140 ꢀC. HRMS (ES) calc. for: C20
H
21
ClNO3 342.1261;
2.12. Preparation of compounds 13i,j from carboxylic acids and
oxalyl chloride
found: 342.1284. 1H NMR (CDCl3): 1.38 (s, 6H), 1.88 (t, 2H, J ¼ 6.8),
2.24 (s, 3H), 2.46 (s, 3H), 2.89 (t, 2H, J ¼ 6.8), 7.00 (s,1H), 7.36 (dd,1H,
J ¼ 0.4 and 8.3), 8.04 (dd, 1H, J ¼ 2.5 and 8.3), 8.83 (d,1H, J ¼ 2.5). 13C
NMR (CDCl3): 12.3,12.5, 20.5, 27.2, 32.7, 74.1,102.2,109.1,118.7,124.1,
124.6, 124.9, 126.6, 134.4, 146.0, 148.4, 149.1, 150.3, 150.7.
In a 40 mL round-bottomed thick glass tube fitted with a PTFE-
faced cap, the relevant acid (2.08 mmol), oxalyl chloride (1.2 mL,
2.40 mmol) and a drop of dimethylformamide were stirred in

L. Alvey et al. / European Journal of Medicinal Chemistry 44 (2009) 2497–2505
2503
dichloromethane (10 mL, dried over 4 Å molecular sieves) for 10 h.
The stock dichloromethane solution of the phosphonium salt 11
(1.67 mmol) described above was then added followed by trie-
thylamine (1.2 mL, 8.4 mmol; dried over 4 Å molecular sieves). This
was refluxed for 64 h before concentrating it to dryness. The
resulting residues containing compounds 13i,j were purified
accordingly as described below.
(m, 2H), 2.82 (t, 2H, J ¼ 6.8), 3.13 (t, 2H, J ¼ 7.0), 3.50 (m, 2H), 3.68
(m, 2H), 6.34 (s, 1H). 13C NMR (CDCl3): 12.0, 12.5, 20.5, 24.9, 27.2,
31.9, 32.9, 41.9, 45.7, 46.3, 55.1, 55.4, 73.8, 101.3, 108.7, 118.2, 121.4,
124.8, 147.7, 148.4, 157.0, 170.5.
2.13.3. 1-[3-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-
f]chromen-2-yl)propanoyl]pyrrolidine (14c)
This compound was obtained as a solid in a 6% yield after
a chromatography over silica gel (dichloromethane/ethanol 95:5).
m.p. ¼115 ꢀC. HRMS (ES) calc. for: C22H30NO3 356.2226; found:
356.2205. 1H NMR (CDCl3): 1.35 (s, 6H), 1.89 (m, 4H), 1.93 (m, 2H),
2.20 (s, 3H), 2.39 (s, 3H), 2.71 (m, 2H), 2.82 (m, 2H), 3.15 (m, 2H),
3.42 (t, 2H, J ¼ 7.4), 3.50 (t, 2H, J ¼ 6.7), 6.34 (s, 1H). 13C NMR
(CDCl3): 12.0, 12.5, 20.6, 24.5, 24.8, 26.5, 27.2, 32.9, 33.5, 73.8, 101.1,
108.7, 118.2, 121.3, 124.9, 147.7, 148.4, 157.3, 170.6.
2.12.1. 2-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]chromen-
2-yl)pyrazine (13i)
This compound was obtained as a solid in a 52% yield after
a chromatography over silica gel (ethyl acetate/cyclohexane 1:3).
m.p. ¼140 ꢀC. HRMS (ES) calc. for: C19H21N2O2 309.1603; found:
309.1587. 1H NMR (CDCl3): 1.37 (s, 6H), 1.87 (t, 2H, J ¼ 6.8), 2.24 (s,
3H), 2.48 (s, 3H), 2.90 (t, 2H, J ¼ 6.8), 7.44 (s,1H), 8.44 (d,1H, J ¼ 2.4),
8.55 (dd, 1H, J ¼ 1.1 and 2.4), 9.13 (d, 1H, J ¼ 1.1). 13C NMR (CDCl3):
12.4, 12.5, 20.4, 27.2, 32.7, 74.1, 106.0, 109.5, 118.9, 124.8, 125.1, 141.4,
143.1, 144.5, 145.9, 148.5, 149.8, 151.8.
2.14. Preparation of compounds 15a–c using microwave heating
2.12.2. 4,5,7,7-Tetramethyl-2-(tetrahydrofuran-2-yl)-8,9-dihydro-
7H-furo[3,2-f]chromene (13j)
In a typical procedure, in a 20 mL Biotage vial, the phosphonium
salt 11 (1.96 g, 3.5 mmol), the corresponding acid (3.5 mmol), DCC
(0.72 g, 3.5 mmol) and hydroxybenzotriazole (0.47 g, 3.5 mmol)
were mixed in acetonitrile (dried over 4 Å molecular sieves, 14 mL).
Triethylamine (2.45 mL, 17.4 mmol) was then added, the vial was
sealed and submitted to the microwave heating (120 ꢀC for 1 h, the
absorbance of the medium being set to high). The resulting
suspension was concentrated to dryness, dispersed in boiling
cyclohexane, filtered and the filtrate was concentrated to dryness
again. The resulting residue was purified as described below to
provide compounds 15a–c.
This compound was obtained as a solid in a 60% yield after
a chromatography over silica gel (dichloromethane/cyclohexane
2:1). m.p. ¼ 98 ꢀC. HRMS (ES) calc. for: C19H25O3 301.1804; found:
301.1818. 1H NMR (CDCl3): 1.36 (s, 6H), 2.04 (t, 2H, J ¼ 6.7), 2.12 (m,
2H), 2.19 (s, 3H), 2.23 (m, 2H), 2.29 (s, 3H), 2.85 (t, 2H, J ¼ 6.7), 3.95
(m, 1H), 4.08 (m, 1H), 5.08 (t, 1H, J ¼ 6.3), 6.54 (s, 1H). 13C NMR
(CDCl3): 12.1, 12.5, 20.5, 26.3, 27.2, 31.1, 32.9, 68.9, 73.8, 75.0, 101.6,
109.6, 118.6, 122.2, 124.2, 147.8, 148.9, 157.4.
2.13. Preparation of compounds 14a–c from succinic amides
2.14.1. (E)-3-(2-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo-
[3,2-f]chromen-2-yl)vinyl)pyridine (15a)
In a 40 mL round-bottomed thick glass tube fitted with a PTFE-
faced cap, succinic anhydride (0.18 g, 1.87 mmol) and the relevant
secondary amine (1.86 mmol) in dichloromethane (5 mL, dried
over 4 Å molecular sieves) were refluxed for 1 h. Upon cooling,
dicyclohexylcarbodiimide (0.39 g, 1.89 mmol) was added and the
solution was stirred for 30 min at room temperature prior to the
addition of the stock dichloromethane solution of the phospho-
nium salt 11 (1.67 mmol) described above and triethylamine
(0.95 mL, 6.8 mmol, dried over 4 Å molecular sieves). This was
heated at 65 ꢀC for 88 h and then concentrated to dryness. The
resulting paste was dispersed in boiling cyclohexane, filtrated and
the filtrate was concentrated to dryness prior to a purification as
described below.
This compound was obtained as a solid in a 22% yield after
a chromatography over neutral alumina containing 1.5% water
(cyclohexane/ethyl acetate 95:5–3:1). m.p. ¼149 ꢀC. HRMS (ES)
calc. for: C22H24NO2 334.1807; found: 334.1810. 1H NMR (CDCl3):
1.37 (s, 6H), 1.87 (t, 2H, J ¼ 6.7), 2.24 (s, 3H), 2.48 (s, 3H), 2.87 (t, 2H,
J ¼ 6.7), 6.67 (s, 1H), 7.06 (d, 1H, J ¼ 16.2), 7.23 (d, 1H, J ¼ 16.2), 7.30
(m, 1H), 7.84 (m, 1H), 8.50 (m, 1H), 8.77 (d, 1H, J ¼ 2.1). 13C NMR
(CDCl3): 11.9, 12.1, 20.1, 26.8, 32.3, 73.6, 105.1, 108.7, 118.1, 118.9,
120.0, 123.5, 123.6, 124.5, 124.8, 132.5, 132.7, 147.7, 148.5, 148.6,
153.3.
2.14.2. 3-(2-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]-
chromen-2-yl)ethyl)pyridine (15b)
2.13.1. 4-[3-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]-
chromen-2-yl)propanoyl]morpholine (14a)
This compound was obtained as an oil in a 10% yield after
a chromatography over neutral alumina containing 1.5% water
(cyclohexane/ethyl acetate 9:1–5:1). HRMS (ES) calc. for:
C22H26NO2 336.1964; found: 336.1961. 1H NMR (CDCl3): 1.35 (s, 6H),
1.84 (t, 2H, J ¼ 7.2), 2.21 (s, 3H), 2.40 (s, 3H), 2.81 (t, 2H, J ¼ 7.2), 3.09
(s, 4H), 6.27 (s, 1H), 7.21 (m, 1H), 7.50 (m, 1H), 8.48 (m, 1H), 8.52
(d, 1H, J ¼ 1.9). 13C NMR (CDCl3): 11.7, 12.1, 20.2, 20.8, 30.1, 31.4, 32.5,
73.4, 101.1, 108.3, 117.9, 121.1, 123.3, 124.3, 135.9, 136.4, 147.3, 147.7,
148.0, 150.0, 156.2.
This compound was obtained as a solid in a 22% yield after two
successive chromatographies over silica gel (dichloromethane/
ethanol 95:5 and then ethyl acetate/cyclohexane 1:3). m.p. ¼120 ꢀC.
HRMS (ES) calc. for: C22H30NO4 372.2175; found: 372.2163. 1H NMR
(CDCl3): 1.35 (s, 6H),1.84 (t, 2H, J ¼ 6.8), 2.20 (s, 3H), 2.39 (s, 3H), 2.76
(t, 2H, J ¼ 6.7), 2.82 (m, 2H), 3.14 (m, 2H), 3.47 (m, 2H), 3.61 (m, 2H),
3.66 (m, 4H), 6.35 (s,1H).13C NMR (CDCl3): 12.1,12.5, 20.6, 24.8, 27.2,
31.8, 32.8, 42.4, 46.3, 67.0, 67.3, 73.8, 101.4, 108.7, 118.1, 121.5, 124.8,
147.8, 148.4, 156.8, 170.7.
2.14.3. 4,5,7,7-Tetramethyl-2-(thiophen-2-yl)-8,9-dihydro-7H-
furo[3,2-f]chromene (15c)
2.13.2. 4-[3-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]-
chromen-2-yl)propanoyl] 1-methylpiperazine (14b)
This compound was obtained as a solid in a 26% yield after
a chromatography over neutral alumina containing 1.5% water
(cyclohexane/dichloromethane 95:5). m.p. ¼102 ꢀC. HRMS (ES)
calc. for: C19H20O2S 313.1262; found: 313.1246. 1H NMR (CDCl3):
1.37 (s, 6H), 1.88 (t, 2H, J ¼ 6.7), 2.20 (s, 3H), 2.46 (s, 3H), 2.89 (t, 2H,
J ¼ 6.7), 6.79 (s, 1H), 7.10 (q, 1H, J ¼ 3.6 and 5.0), 7.31 (q, 1H, J ¼ 1.0
and 5.0), 7.45 (q, 1H, J ¼ 1.0 and 3.6). 13C NMR (CDCl3): 11.8, 12.1,
This compound was obtained as a solid in a 39% yield after
a chromatography over silica gel (dichloromethane/2 N ethanolic
ammonia 95:5). m.p. ¼ 86 ꢀC. HRMS (ES) calc. for: C23H33N2O3
385.2491; found: 385.2502. 1H NMR (CDCl3): 1.34 (s, 6H), 1.84 (t,
2H, J ¼ 6.8), 2.29 (s, 3H), 2.34 (s, 3H), 2.38 (m, 2H), 2.40 (s, 3H), 2.77

2504
L. Alvey et al. / European Journal of Medicinal Chemistry 44 (2009) 2497–2505
20.1, 26.8, 32.4, 73.6, 99.8, 108.5, 118.1, 122.5, 123.5, 123.6, 124.3,
124.9, 127.7, 134.2, 147.7, 148.0, 150.1.
(m, 2H), 5.51 (m, 1H), 6.48 (dd, 1H, J ¼ 0.4 and 8.6), 7.86 (dd, 1H,
J ¼ 2.3 and 8.1), 8.60 (m, 1H). 13C NMR (CDCl3): 11.7, 12.0, 20.2, 26.7,
26.8, 32.5, 41.2, 45.4, 58.0, 73.5, 97.2, 106.6, 108.2, 116.9, 118.0, 121.5,
125.1, 133.8, 145.1, 147.6, 147.9, 153.5, 158.3.
2.14.4. 4,5,7,7-Tetramethyl-2-(thiophen-2-ylmethyl)-8,9-dihydro-
7H-furo[3,2-f]chromene (15d)
This compound was also obtained using the microwave heating
described above, although from the corresponding commercially
available acyl chloride, as a low melting solid in a 33% yield after
a chromatography over neutral alumina containing 1.5% water
(cyclohexane/dichloromethane 95:5). HRMS (ES) calc. for:
C20H22O2S 327.1419; found: 327.1439. 1H NMR (CDCl3): 1.35 (s, 6H),
1.84 (t, 2H, J ¼ 6.7), 2.20 (s, 3H), 2.40 (s, 2H), 2.82 (t, 2H, J ¼ 6.7), 4.31
(s, 2H), 6.35 (s, 1H), 6.98 (m, 2H), 7.21 (m, 2H). 13C NMR (CDCl3):
11.6, 12.1, 20.1, 26.8, 29.4, 32.5, 73.4, 101.5, 108.4, 118.0, 121.3, 124.2,
124.3, 125.8, 126.8, 140.0, 147.4, 148.3, 155.4.
2.18. 5-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]chromen-2-
yl)pyridine-2-carbonitrile (19)
Compound 13d (0.47 g, 1.38 mmol), zinc cyanide (0.1 g,
0.9 mmol), zinc (0.025 g, 0.38 mmol) and [1,10-bis(diphenylphos-
phino)ferrocene]dichloropalladium (II) complexed with dichloro-
methane (0.005 g, 0.007 mmol) were mixed in dimethylacetamide
(3 mL, dried over 4 Å molecular sieves). This was degassed by
bubbling argon through the solution and then heated at 120 ꢀC for
2 h. The cooled solution was diluted in dichloromethane, washed
with water and brine and the organic phase dried over magnesium
sulfate. After concentration to dryness, the residue was purified by
chromatography over silica gel (dichloromethane) leading to
compound 19 as a solid (0.46 g, 79%). m.p. ¼194 ꢀC. HRMS (ES) calc.
for: C21H21N2O2 333.1603; found: 333.1622. 1H NMR (CDCl3): 1.39
(s, 6H), 1.90 (t, 2H, J ¼ 6.8), 2.25 (s, 3H), 2.47 (s, 3H), 2.91 (t, 2H,
J ¼ 6.8), 7.18 (s, 1H), 7.72 (dd, 1H, J ¼ 0.6 and 8.1), 8.18 (dd, 1H, J ¼ 2.2
and 8.1), 9.13 (dd, 1H, J ¼ 0.6 and 2.2). 13C NMR (CDCl3): 12.1 (two
signals), 20.5, 27.2, 32.6, 74.2, 104.8, 109.4, 117.8, 118.9, 124.8, 125.5,
128.8, 130.4, 131.6, 131.8, 147.3, 148.7, 149.7, 149.7, 149.8.
2.15. 4,5,7,7-Tetramethyl-2-(pyridin-3-yl)-7H-furo[3,2-f]chromen-
9(8H)-one (16)
Compound 13a (0.11 g, 0.36 mmol) was dissolved in a mixture of
acetonitrile (10 mL), water (1 mL) and dichloromethane (4 mL).
This was cooled to ꢁ42 ꢀC and cerium ammonium nitrate (0.8 g,
1.46 mmol) dissolved in a water (2 mL)–acetonitrile (2 mL) mixture
was added. The temperature was allowed to warm to room
temperature for 1 h and the mixture was diluted in dichloro-
methane. The organic phase was washed with water and dried over
magnesium sulfate. The residue obtained after concentration to
2.19. 5-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]chromen-2-
yl)-2-(2H-tetrazol-5-yl)pyridine (20)
dryness was purified by
a chromatography over silica gel
(dichloromethane/ethyl acetate 3:1) leading to compound 16 as
a solid (0.085 g, 74%). m.p. ¼182 ꢀC. HRMS (ES) calc. for: C20H20NO3
322.1443; found: 322.1461. 1H NMR (CDCl3): 1.51 (s, 6H), 2.25 (s,
3H), 2.53 (s, 3H), 2.76 (s, 2H), 7.38 (m, 1H), 7.86 (s, 1H), 8.15 (m, 1H),
8.59 (m, 1H), 9.15 (m, 1H). 13C NMR (CDCl3): 12.2, 13.4, 27.1, 49.3,
79.6, 105.0, 110.2, 123.6, 123.7, 124.0, 127.2, 129.3, 132.3, 146.5, 149.4,
149.7, 154.7, 156.5, 193.5.
Compound 19 (0.15 g, 0.46 mmol), sodium azide (0.07 g,
1.08 mmol) and triethylamine hydrochloride (0.18 g, 1.31 mmol)
were dispersed in toluene (12 mL). This was heated at 80 ꢀC for 12 h
and LC/MS monitoring pointed out the presence of large amount of
starting material. Thus another amount of sodium azide (0.065 g,
1.0 mmol) and triethylamine hydrochloride (0.14 g, 1.02 mmol) was
added and LC/MS monitoring was repeated after about every 10 h.
Accordingly, the same quantity of sodium azide and triethylamine
hydrochloride was repeatedly added until the completion of the
reaction. This required the operation to be repeated four more times.
Afterconcentration todryness, the residuewas cautiously made acid
with acetic acid (1 mL) and the resulting mixture was purified by
a chromatography over silica gel (dichloromethane/ethanol/acetic
acid 95:5:0.1) leading to compound 20 as a solid (0.15 g, 89%).
m.p. > 260 ꢀC. HRMS (ES) calc. for: C21H22N5O2 376.1774; found:
376.1794. 1H NMR (CDCl3): 1.31 (s, 6H), 1.84 (t, 2H, J ¼ 6.8), 2.14 (s,
3H), 2.43 (s, 3H), 2.88 (t, 2H, J ¼ 6.8), 7.70 (s,1H), 8.29 (d,1H, J ¼ 8.2),
8.47 (d,1H, J ¼ 8.2), 9.29 (s,1H). 13C NMR (CDCl3): 12.7 (two signals),
20.4, 27.4, 32.4, 74.5, 105.0, 109.9, 118.6, 123.6, 124.0, 125.4, 128.9,
133.4, 143.2, 146.6, 148.4, 149.0, 151.1, 155.6.
2.16. 3-(4,5,7,7-Tetramethyl-8,9-dihydro-7H-furo[3,2-f]chromen-2-
yl)pyridine 1-oxide (17)
Compound 13a (0.2 g, 0.65 mmol) and 3-chloroperbenzoic acid
(77%; 0.3 g, 1.30 mmol) were stirred overnight in dichloromethane
(40 mL). The resulting solution was washed with a 1 N sodium
hydroxide solution then with water and then dried over sodium
sulfate. The residue obtained after concentration to dryness was
further purified by a chromatography over silica gel (dichloro-
methane/ethanol 96:4) leading to compound 17 as a solid (0.11 g,
52%). m.p. ¼176 ꢀC. HRMS (ES) calc. for:C20H22NO3 324.1600; found:
324.1613. 1H NMR (CDCl3): 1.36 (s, 6H), 1.87 (t, 2H, J ¼ 6.8), 2.23 (s,
3H), 2.43 (s, 3H), 2.89 (t, 2H, J ¼ 6.8), 7.04 (s,1H), 7.32 (m,1H), 7.67 (m,
1H), 8.12 (m, 1H), 8.72 (s, 1H). 13C NMR (CDCl3): 12.0 (two signals),
18.4, 20.1, 26.8, 32.2, 73.8,103.6,108.9,118.5,121.4,124.2,127.7,125.9,
130.7, 135.2, 137.5, 148.2, 148.5, 149.0.
2.20. Methyl 5-(4,5,7,7-tetramethyl-8,9-dihydro-7H-furo[3,2-f]-
chromen-2-yl)pyridine-2-carboximidoate (21)
2.17. N1,N1-Dimethyl-N3-(5-(4,5,7,7-tetramethyl-8,9-dihydro-7H-
furo[3,2-f]chromen-2-yl)pyridin-2-yl)propane-1,3-diamine (18)
The nitrile-bearing compound 15 (0.44 g, 1.33 mmol) was dis-
solved in methanol (10 mL, dried over 4 Å molecular sieves) and
potassium terbutanolate (0.18 g, 1.65 mmol) was added. This was
stirred under an inert atmosphere at room temperature for three
days. The resulting precipitate was then filtered and dried under
vacuum to provide pure compound 21 as a solid (0.44 g, 92%).
m.p. ¼135 ꢀC. HRMS (ES) calc. for: C22H24N2O3 365.1865; found:
365.1884. 1H NMR (CDCl3): 1.38 (s, 6H), 1.89 (t, 2H, J ¼ 6.8), 2.24 (s,
3H), 2.48 (s, 3H), 2.91 (t, 2H, J ¼ 6.8), 4.08 (s, 3H), 7.10 (s, 1H), 7.89
(dd, 1H, J ¼ 0.5 and 8.2), 8.17 (dd, 1H, J ¼ 2.2 and 8.2), 9.10 (dd, 1H,
J ¼ 0.5 and 2.2), 9.21 (s (exch.), 1H). 13C NMR (CDCl3): 12.4
Compound 13d (0.10 g, 0.29 mmol) was heated to reflux under
an inert atmosphere in N1,N1-dimethylpropane-1,3-diamine
(4 mL) for 12 h. The resulting solution was concentrated to dryness
using a high vacuum pump and the residue was purified by
a chromatography over neutral alumina containing 1.5% water
(dichloromethane/ethanol 98:2) leading to compound 18 as a wax
(0.08 g, 63%). HRMS (ES) calc. for: C25H34N3O2 408.2651; found:
408.2637. 1H NMR (CDCl3): 1.37 (s, 6H), 1.89 (m, 4H), 2.22 (s, 3H),
2.31 (s, 6H), 2.45 (s, 3H), 2.49 (t, 2H, J ¼ 6.7), 2.89 (t, 2H, J ¼ 6.7), 3.44

L. Alvey et al. / European Journal of Medicinal Chemistry 44 (2009) 2497–2505
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124.4, 124.9, 129.0, 132.5, 145.7, 146.2, 148.4, 149.4, 151.2, 167.0.
Acknowledgement
´
We thank Gerard Gastine and Manon Vandervennet for their
careful technical assistance in bacteriology. We thank Sanofi-
Aventis as well as Pfizer for very generous donations of scientific
equipment. This work received the financial support of the Institut
Pasteur (GPH-5, DVPI) and the European Community (LHSP-CT-
2005-018923).
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