A click chemistry approach to secosteroidal macrocycles

Article abstract of DOI:10.1016/j.steroids.2013.12.002

A new synthetic pathway towards secosteroidal macrocycles was described via a reaction of cycloaddition as the key step. The characteristic ¹H and ¹³C NMR spectroscopic features of the synthesized compounds are reported.

Full text of DOI:10.1016/j.steroids.2013.12.002

Steroids 80 (2014) 102–110
Contents lists available at ScienceDirect
Steroids
journal homepage: www.elsevier.com/locate/steroids
A click chemistry approach to secosteroidal macrocycles
⇑
Malika Ibrahim-Ouali , Khalil Hamze
Aix Marseille Université, Centrale Marseille, CNRS, iSm2 UMR 7313, 13397 Marseille, France
a r t i c l e i n f o
a b s t r a c t
Article history:
A
new synthetic pathway towards secosteroidal macrocycles was described via a reaction of
cycloaddition as the key step. The characteristic 1H and 13C NMR spectroscopic features of the
synthesized compounds are reported.
Received 13 September 2013
Received in revised form 25 November 2013
Accepted 9 December 2013
Available online 18 December 2013
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Cholic acid
Macrocycles
‘Click chemistry’
1,2,3-Triazole
1. Introduction
continuing research into new classes of antimicrobial agents.
1,2,3-Triazole-containing molecules is one of these classes.
Secosteroids have attracted considerable interest because of the
broad range of biological activities of many naturally occurring
representatives, such as vitamins D [1], with anolides [2], and
marine steroids [3,4]. Apart from Vitamins D with their innumera-
ble biological effects [5], secosteroids with cytotoxic [6–8],
antihistamine [9], and anticancer [10] activity should be
mentioned as compounds with great potential for drug develop-
ment. The activity of seco analogs of normal steroidal hormones
in humans and higher animals is a matter of scientific interest as
well. Some of these compounds were prepared synthetically and
showed hormonal or antihormonal activity [11–18]. It is evident
that the higher conformational flexibility of seco steroids in
comparison with normal steroids may result in novel, pharmaceu-
tically useful compounds.
Moreover, [1,2,3]-triazoles are important class of five-
membered nitrogen heterocycles. They have been reported to have
important biological activities, including anti-HIV [19], anti-tumor
[20], anti-bacterial [21], and anti-tuberculosis [22], and can also act
as glycosidase [23–24], tyronase [25], and serine hydrolase [26]
inhibitors.
1,2,3-Triazole moieties are attractive connecting units because
they are stable to metabolic degradation and capable of hydrogen
bonding, which can be favorable in the binding of biomolecular
targets and can improve the solubility [27,28]. The 1,2,3-triazole
moiety does not occur in nature, although the synthetic molecules
that contain 1,2,3-triazole units show diverse biological activities.
The importance of triazolic compounds in medicinal chemistry is
undeniable. Contrary to other azaheterocycles, the 1,2,3-triazole ring
is not protonated at physiological pH because of its poor basicity.
Recently, Pore and co-workers [29,30] reported the synthesis of
novel 1,2,3-triazole-linked b-lactam-bile acid conjugates A and
some dimeric compounds B by 1,3-dipolar cycloaddition reaction
of azido b-lactam and terminal alkyne of bile acids by using a click
reaction (Scheme 1). Most of the compounds exhibited significant
antifungal and moderate antibacterial activity against all the tested
strains.
The unique chemistry behavior of this moiety aroused the
chemist’s interest, ranging from a synthetic point of view to the
context of biological and pharmacological application.
So, for some years, we have been interested to develop new
synthetic approaches to prepare secosteroidal molecules. Herein,
we report a new and simple preparation of secocholanic steroids
possessing a macrocycle and a triazole unit in their structure.
Indeed, this combination of secocholanic skeleton with varied
types of macrocycles, produces high levels of skeletal diversity
and complexity. Additionally, there are no example, which
describe the application of the copper-catalyzed azide–alkyne
cycloaddition (CuAAC) reaction for the synthesis of secosteroids.
We report here the full details of these syntheses.
The incidence of life-threatening fungal infections has tremen-
dously increased in the last two decades due to greater use of
immunosuppressive drugs, prolonged use of broad spectrum
antibiotics, widespread use of indwelling catheters, and also in
cancer and AIDS patients. The presently marketed antifungal and
antibacterial drugs are either highly toxic or becoming ineffective
due to the appearance of resistant strains. This necessitates
⇑
Corresponding author. Tel.: +33 491288416; fax: +33 491983865.
E-mail address: malika.ibrahim@univ-amu.fr (M. Ibrahim-Ouali).
0039-128X/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.steroids.2013.12.002

M. Ibrahim-Ouali, K. Hamze / Steroids 80 (2014) 102–110
103
O
X
OH
O
R
H
O
N
X
N
H
OH
OH
N
OH
N
R
O
H
Ph
N
H
N
OH
N
Ph
N
N
H
N
H
O
A
N
OCH3
R
OH
X
R'
O
X = O/NH; R = H/OH and R' = H/Cl
B
Scheme 1. Bile acid derivatives with biological activities.
3.29 (m, 1H, H-12), 4.76 (d, J = 2.8 Hz, 1H, H-25); 13C NMR
(75 MHz, CDCl3): 17.7, 19.9, 24.8, 27.6, 28.8, 29.2, 31.4, 34.2,
34.7, 35.6, 36.9, 37.1, 40.2, 44.4, 45.6, 49.1, 52.0, 53.4, 56.9, 57.2,
58.0, 63.1, 67.9, 73.6, 76.2, 77.8, 79.1, 82.3, 173.1. HRMS (EI) for
2. Experimental section
All reactions were run under argon in oven-dried glassware. 1H
and 13C NMR spectra are recorded at 200 or 400 and 50 and
100 MHz respectively, in CDCl3 solutions. Chemical shift (d) are
reported in ppm with tetramethylsilane as internal standard. IR
spectra were recorded on a Perkin–Elmer 1600 spectrophotometer.
C
29H46O5 [M+] calcd 474.3345 found 474.3348.
Flash chromatography was performed on silica gel (Merk 60 F254
)
2.3. Propionyl ether of 3a,7a-dimethoxy-12a-hydroxy-5b-cholane (4)
and TLC on silica gel. Dichloromethane was distilled from P2O5
and tetrahydrofuran (THF) over sodium/benzophenone.
Compounds 14 and 15 were prepared according to the previ-
ously described procedure [31]. The nomenclature used for the ste-
roids is not the nomenclature used by Chemical Abstracts [32,33].
A flask equipped with a magnetic stirring bar, an argon outlet
and a condenser was charged with NaBH4 (90 mg, 0.40 mmol)
and anhydr. THF (7 mL)–diglyme (3 mL) under argon. The solution
was cooled at 0 °C and then a solution composed of boron trifluor-
ide etherate (0.42 g, 3 mmol), ester 3 (0.18 mmol) and anhydr. THF
(5 mL) was added. After completion of the reaction (TLC), it was
quenched by addition of 2 N hydrochloric acid (1 mL) and water
(10 mL), the product was extracted with ether (3 Â 20 mL). The
extracts were dried over MgSO4, filtered and then concentrated
under vacuum. The residue was chromatographed on silica gel
(Et2O–petroleum ether 1:1). Yield 46 mg (56%). Oil IR (neat)
2.1. Propargyl 3a,7a,12a-trihydroxy-5b-cholan-24-oate (2)
A solution of cholic acid 1 (320 mg, 0.78 mmol), propargyl bro-
mide (0.14 g, 1.63 mmol), N,N-dicyclohexylcarbodiimide (0.14 g,
0.70 mmol) and 4-dimethyl-aminopyridine (86 mg, 0.70 mmol) in
dichloromethane (5 mL) was stirred at room temperature until
the reaction was completed (about 12 h). The N,N-dicyclohexyl
urea was filtered off and the filtrate was washed with water, 5%
acetic acid solution and again water, dried over magnesium sulfate
and the solvent was evaporated to afford propargyl cholate 2
3280, 1220, 1070 cmÀ1 1H NMR (300 MHz, CDCl3): 0.66 (s, 3H,
;
H-18), 0.81 (d, J = 6.5, 3H, H-21), 0.92 (s, 3H, H-19), 2.42
(t, J = 2.4 Hz, 1H, H-27), 2.89 (m, 1H, H-3), 3.16 (s, 3H, OCH3),
3.18 (s, 3H, OCH3), 3.24 (m, 1H, H-7), 3.32 (m, 1H, H-12), 4.27
(d, J = 2.6 Hz, 1H, H-25); 13C NMR (75 MHz, CDCl3): 17.4, 20.1,
24.7, 27.9, 29.1, 30.6, 32.7, 33.9, 34.6, 35.8, 37.1, 37.4, 40.8, 43.4,
45.1, 49.3, 51.4, 52.8, 57.1, 57.4, 59.0, 62.7, 67.4, 70.2, 72.6, 74.4,
76.9, 78.1, 80.3. HRMS (EI) for C29H48O4 [M+] calcd 460.3553 found
460.3559.
(260 mg, 75%) as an oil. IR (neat) 3280, 1736, 1220, 1070 cmÀ1
;
1H NMR (300 MHz, CDCl3): 0.68 (s, 3H, H-18), 0.98 (d, J = 6.4 Hz,
3H, H-21), 1.18 (s, 3H, H-19), 2.48 (t, J = 2.4 Hz, 1H, H-27), 2.87
(m, 1H, H-7), 2.92 (m, 1H, H-3), 3.42 (m, 1H, H-12), 4.67
(d, J = 2.8 Hz, 1H, H-25); 13C NMR (75 MHz, CDCl3): 17.4, 20.4,
24.3, 27.7, 29.2, 29.8, 31.6, 34.7, 34.6, 35.0, 35.9, 37.4, 40.6, 45.4,
46.6, 49.6, 51.8, 53.5, 57.6, 63.4, 68.3, 74.8, 76.5, 77.9, 79.8, 79.9,
173.4. HRMS (EI) for
446.3036.
C
27H42O5 [M+] calcd 446.3032 found
2.4. Propionyl ether of 3a,7a-dimethoxy-12-oxo-5b-cholane (5)
Alcohol 4 (1 g, 2.17 mmol) was mixed in a mortar with pyridi-
nium chlorochromate (PCC) (0.57 g, 2.66 mmol). The mixture was
transferred to a pressure-resistant tube (Pyrex) and irradiated with
MW at 170 °C for 5 min. The reaction mixture was filtered through
a Celite pad and the filtrate and washings (CH2Cl2, 3 ⁄ 10 mL) were
combined and evaporated under reduced pressure. The residue
was chromatographed on silica gel (diethyl ether/petroleum ether:
7/3), to afford 0.68 g (68% yield) of 12-oxo steroid 5 as an oil. IR
2.2. Propargyl 3a,7a-dimethoxy-12a-hydroxy-5b-cholan-24-oate (3)
To a stirred suspension of NaH (0.62 g, 26 mmol) in THF (10 mL)
at 0 °C under argon was added a solution of triol 2 (5 g, 11.8 mmol)
in 5 mL of THF. The reaction mixture was stirred for 15 min, and
then iodomethane (367 lL, 5.9 mmol) was added dropwise. After
24 h at room temperature, the reaction was diluted with 10 mL
of Et2O and quenched by the slow addition of 10 mL of H2O. The
combined organic extracts were washed with 30 mL of brine, dried
over anhydrous MgSO4, and concentrated in vacuo. The crude prod-
uct was purified by flash chromatography on silica gel (Et2O: 100%)
to give 3 (4.6 g, 86%) as a white solid. mp = 132 °C; 1H NMR
(300 MHz, CDCl3): 0.62 (s, 3H, H-18), 0.83 (d, J = 6.5, 3H, H-21),
0.86 (s, 3H, H-19), 2.46 (t, J = 2.4 Hz, 1H, H-27), 2.94 (m, 1H,
H-3), 3.14 (s, 3H, OCH3), 3.18 (s, 3H, OCH3), 3.21 (m, 1H, H-7),
(neat) 3236, 1511 cmÀ1 1H NMR (300 MHz, CDCl3): 0.72 (s, 3H,
;
H-18), 0.86 (d, J = 6.4, 3H, H-21), 0.91 (s, 3H, H-19), 2.47 (t,
J = 2.1 Hz, 1H, H-27), 2.86 (m, 1H, H-3), 3.17 (s, 3H, OCH3), 3.18
(s, 3H, OCH3), 3.26 (m, 1H, H-7), 4.16 (d, J = 2.3 Hz, 1H, H-25);
13C NMR (75 MHz, CDCl3): 16.9, 20.3, 23.6, 27.4, 29.3, 30.1, 32.6,
33.4, 34.1, 36.2, 37.3, 38.4, 41.5, 43.6, 44.9, 49.6, 51.7, 52.1, 56.8,
57.9, 59.2, 61.9, 66.4, 69.9, 72.3, 75.7, 79.0, 81.1, 214.9. HRMS
(EI) for C29H46O4 [M+] calcd 458.3396 found 458.3400.

104
M. Ibrahim-Ouali, K. Hamze / Steroids 80 (2014) 102–110
2.5. 3
a,7
a-Dimethoxy-13-oxa-C-homo-cholan-12-one (6)
2.8. Azido precursor (9)
To a solution of ketone 5 (0.5 g, 1.09 mmol) in dry dichloro-
methane (30 mL) containing p-toluenesulfonic acid (167 mg,
1.09 mmol) m-CPBA (12 mg) was added. The solution was stirred
for 24 h at room temperature. The solution was then diluted with
water and extracted with dichloromethane (3 ⁄ 15 mL). The solu-
tion was washed successively with a 5% Na2S2O3 solution, satu-
rated brine, and water and was dried over anhydrous magnesium
sulfate. The oily product, obtained by evaporation of the solvent,
was purified by flash chromatography on silica gel (CH2Cl2/MeOH:
95/5) to afford 0.5 g of pure lactone 6 (96%) as an oil. 1H NMR
(300 MHz, CDCl3): 0.68 (s, 3H, H-18), 0.89 (d, J = 6.4, 3H, H-21),
0.99 (s, 3H, H-19), 2.44 (t, J = 2.1 Hz, 1H, H-27), 2.78 (m, 1H, H-
3), 3.16 (s, 3H, OCH3), 3.19 (s, 3H, OCH3), 3.24 (m, 1H, H-7), 4.16
(d, J = 2.3 Hz, 1H, H-25); 13C NMR (75 MHz, CDCl3): 17.1, 21.3,
24.2, 27.8, 29.1, 30.9, 32.7, 33.6, 35.5, 36.7, 37.4, 37.9, 41.7, 42.8,
43.7, 49.2, 50.9, 52.3, 56.6, 57.5, 58.8, 67.4, 69.1, 71.9, 74.6, 77.6,
79.2, 80.6, 174.3. HRMS (EI) for C29H46O5 [M+] calcd 474.3345
found 474.3348.
Chloro derivative 8 (288 mg, 0.52 mmol) was dissolved in dry
DMF (8 mL). To the solution, sodium azide (201.5 mg, 3.1 mmol)
was added. The reaction mixture was heated at 60 °C for 24 h. Then
the mixture was poured onto crushed ice and extracted with
AcOEt. Organic layer was washed with water solution of NaHCO3
(5%, 3 Â 15 mL), brine (3 Â 15 mL), water (2 Â 20 mL) and dried
over MgSO4. The solvent was evaporated under reduced pressure
and obtained crude product was purified by column chromatogra-
phy (hexane/AcOEt: 5/1) to give secosteroidal derivative
(180 mg, 62%) as a colourless oil. IR (neat) 3286, 2935, 2123,
1721 cmÀ1 1H NMR (300 MHz, CDCl3): 0.76 (s, 3H, H-18), 0.92
9
;
(d, J = 6.4, 3H, H-21), 1.06 (s, 3H, H-19), 2.49 (t, J = 2.2 Hz, 1H, H-
27), 2.86 (m, 1H, H-3), 3.17 (s, 3H, OCH3), 3.18 (s, 3H, OCH3),
3.32 (m, 1H, H-7), 3.51 (s, 2H, CH2N3); 4.09 (m, 2H, H-12), 4.21
(d, J = 2.3 Hz, 1H, H-25); 13C NMR (75 MHz, CDCl3): 17.9, 21.3,
24.2, 27.8, 30.4, 31.6, 32.7, 33.1, 35.9, 36.6, 37.4, 39.8, 40.7, 41.6,
42.5, 47.9, 51.6, 52.3, 54.6, 56.7, 57.9, 59.7, 61.6, 66.8, 69.1, 70.4,
72.7, 76.4, 78.6, 81.2, 169.9. HRMS (EI) for C31H51N3O6 [M+] calcd
561.3778 found 561.3780.
2.6. 3a,7a-Dimethoxy-11,12-seco-5b-cholan-12,13a-diol (7)
2.9. Macrocycle (10)
A solution of propargyl ether 6 (1 g, 2.11 mmol) in dry ether
(10 mL) was added in one portion to a suspension of LiAlH4
(0.25 g, 6.46 mmol) in dry ether (20 mL) at room temperature.
After 1 h the reaction was quenched with H2O and EtOAc. The
aqueous layer was acidified to pH 2 with diluted HCl, and layers
were separated. The aqueous layer was further extracted with
EtOAc (3 Â 50 mL), and the combined organic layers were dried
over anhydrous MgSO4 and evaporated to dryness. The crude prod-
uct was purified by flash chromatography on silica gel (CH2Cl2/
MeOH: 9/1) to afford 0.86 g of pure triol 7 (85%) as an oil. IR (neat)
A mixture of the steroidal azide (115 mg, 0.2 mmol), CuSO4Á5H2-
O (0.03 mmol, 7.5 mg), sodium ascorbate (0.076 mmol, 15 mg),
DMF (2 mL) and water (2 mL) was stirred under argon at room
temperature for 12 h. Then, brine (3 mL) was added and the mix-
ture extracted with CH2Cl2 (3 Â 5 mL). The organic layers were
combined, washed with brine (3 mL) and dried over MgSO4. The
solvent was removed under vacuum and the product was purified
by column chromatography (hexane/AcOEt: 1/1) to afford the de-
sired secosteroidal macrocycle (75 mg, 66%) as an oil. IR (neat)
2950, 1606, 1089 cmÀ1
;
1H NMR (300 MHz, CDCl3): 0.76 (s, 3H, H-
3231, 1704 cmÀ1 1H NMR (300 MHz, CDCl3): 0.74 (s, 3H, H-18),
;
18), 0.92 (d, J = 6.4, 3H, H-21), 1.02 (s, 3H, H-19), 2.46 (t, J = 2.3 Hz,
1H, H-27), 2.81 (m, 1H, H-3), 3.17 (s, 3H, OCH3), 3.19 (s, 3H, OCH3),
3.29 (m, 1H, H-7), 4.23 (d, J = 2.4 Hz, 1H, H-25); 13C NMR (75 MHz,
CDCl3): 19.8, 21.6, 24.9, 27.4, 28.8, 31.4, 32.5, 33.1, 36.3, 36.6, 37.7,
38.4, 40.7, 41.6, 42.9, 49.7, 51.1, 52.7, 57.9, 59.1, 59.8, 61.7, 66.9,
69.3, 71.2, 73.6, 76.5, 78.6, 82.1. HRMS (EI) for C29H50O5 [M+] calcd
478.3658 found 478.3661.
0.98 (d, J = 6.4, 3H, H-21), 1.04 (s, 3H, H-19), 2.81 (m, 1H, H-3),
3.16 (s, 3H, OCH3), 3.17 (s, 3H, OCH3), 3.26 (m, 1H, H-7), 4.13 (m,
2H, H-12), 4.66 (s, 2H, H-25), 4.72 (s, 2H, CH2N), 7.56 (s, 1H,
CH@); 13C NMR (75 MHz, CDCl3): 18.2, 21.9, 24.6, 27.4, 30.9,
32.3, 33.8, 34.1, 35.7, 36.9, 37.2, 39.3, 40.6, 41.5, 42.9, 46.3, 50.9,
52.7, 56.3, 56.1, 57.4, 61.7, 62.5, 66.1, 68.4, 69.7, 72.3, 77.4,
121.6, 142.8, 170.7. HRMS (EI) for
561.3778 found 561.3782.
C
31H51N3O6 [M+] calcd
2.7. Halogenated precursor (8)
2.10. Macrocycle (11)
Compound 7 (100 mg, 0.2 mmol) was dissolved in toluene
(10 mL). To the homogenous solution CaH2 (82.3 mg, 1.96 mmol),
benzyltriethylammonium chloride (4.5 mg, 0.02 mmol) and
chloroacetic chloride (0.054 mL, 0.67 mmol) were added. The
suspension was refluxed for 3 h. Then it was cooled to room
temperature and filtered. The filtrate was diluted with toluene
(30 mL) and washed with water solution of NaHCO3 (5%,
3 Â 15 mL), brine (3 Â 15 mL), water (2 Â 20 mL) and dried over
MgSO4. The solvent was evaporated under reduced pressure and
obtained crude product was purified by column chromatography
(hexane/AcOEt: 6/1) to give secosteroidal derivative 8 (80 mg,
A flask equipped with a magnetic stirring bar, an argon outlet
and a condenser was charged with NaBH4 (90 mg, 0.40 mmol)
and anhydr. THF (7 mL)–diglyme (3 mL) under argon. The solution
was cooled at 0 °C and then a solution composed of boron trifluor-
ide etherate (0.42 g, 3 mmol), macrocycle 10 (0.18 mmol) and
anhydr. THF (5 mL) was added. After completion of the reaction
(TLC), it was quenched by addition of 2 N hydrochloric acid
(1 mL) and water (10 mL), the product was extracted with ether
(3 Â 20 mL). The extracts were dried over MgSO4, filtered and then
concentrated under vacuum. The residue was chromatographed on
silica gel (Et2O–petroleum ether 1:1), to give macrocycle 11
70%) as
a
yellow oil. IR (neat) 3419, 3289, 2937, 2129,
1717 cmÀ1
;
1H NMR (300 MHz, CDCl3): 0.72 (s, 3H, H-18), 0.96
(43 mg, 44%). IR (neat) 2951, 1175, 1096 cmÀ1 1H NMR
;
(d, J = 6.4, 3H, H-21), 1.04 (s, 3H, H-19), 2.43 (t, J = 2.2 Hz, 1H,
H-27), 2.83 (m, 1H, H-3), 3.16 (s, 3H, OCH3), 3.18 (s, 3H, OCH3),
3.33 (m, 1H, H-7), 4.08 (m, 2H, H-12), 4.17 (d, J = 2.4 Hz, 1H,
H-25), 4.46 (s, 2H, CH2Cl); 13C NMR (75 MHz, CDCl3): 18.8, 20.9,
23.3, 27.6, 29.4, 31.7, 32.2, 32.9, 35.7, 36.3, 37.9, 39.3, 40.6, 40.9,
41.7, 43.0, 48.7, 50.9, 52.6, 56.3, 58.4, 59.2, 61.1, 67.3, 68.6, 70.2,
72.9, 76.3, 78.4, 81.7, 167.3. HRMS (EI) for C31H51ClO6 [M+] calcd
554.3374 found 554.3379.
(300 MHz, CDCl3): 0.72 (s, 3H, H-18), 0.99 (d, J = 6.4, 3H, H-21),
1.06 (s, 3H, H-19), 2.83 (m, 1H, H-3), 3.16 (s, 3H, OCH3), 3.18 (s,
3H, OCH3), 3.32 (m, 1H, H-7), 4.17 (m, 2H, H-12), 4.38 (m, 4H,
OCH2CH2N), 4.69 (s, 2H, H-25), 7.63 (s, 1H, CH@); 13C NMR
(75 MHz, CDCl3): 17.9, 22.3, 24.4, 27.7, 31.2, 32.6, 33.4, 34.6,
35.1, 36.6, 37.3, 39.6, 40.1, 41.7, 43.5, 47.6, 51.2, 52.6, 56.9, 57.1,
57.7, 61.6, 62.3, 66.8, 67.9, 68.1, 69.3, 72.6, 78.1, 121.4, 142.0.
HRMS (EI) for C31H53N3O5 [M+] calcd 547.3985 found 547.3989.

M. Ibrahim-Ouali, K. Hamze / Steroids 80 (2014) 102–110
105
2.11. Macrocycle (12)
2.14. 3a,12a-Dihydroxy-7-oxo-8-oxa-B-homo-5b-cholane (15)
To a solution of macrocycle 11 (50 mg, 0.10 mmol) in chloro-
form (20 mL) was added trimethylsilyl iodide (0.1 mL). The solu-
tion was left overnight at room temperature. Methanol was then
added to decompose any excess trimethylsilyl iodide. The solution
was extracted with diethyl ether, washed with water and saturated
brine, dried over anhydrous magnesium sulfate. Evaporation of the
solvent gave a crude product, which was purified by chromatogra-
phy on silica gel (CH2Cl2/MeOH: 95/5), to give triol 12. Yield 47 mg
To a solution of ketone 14 (0.5 g, 1.11 mmol) in dry dichloro-
methane (30 mL) containing p-toluenesulfonic acid (167 mg,
1.11 mmol) m-CPBA (12 mg) was added. The solution was stirred
for 24 h at room temperature. The solution was then diluted with
water and extracted with dichloromethane (3 ⁄ 15 mL). The
solution was washed successively with a 5% Na2S2O3 solution,
saturated brine, and water and was dried over anhydrous magne-
sium sulfate. The oily product, obtained by evaporation of the
solvent, was purified by flash chromatography on silica gel
(CH2Cl2/MeOH: 95/5) to afford 0.51 g of pure lactone 15 (98%) as
an oil. 1H NMR (300 MHz, CDCl3): 0.66 (s, 3H, H-18), 0.89 (d,
J = 6.4 Hz, 3H, H-21), 0.98 (s, 3H, H-19), 2.48 (t, J = 2.3 Hz, 1H,
H-27), 2.96 (m, 1H, H-3), 3.42 (m, 1H, H-12), 3.86 (m, 1H, H-8),
3.49 (m, 1H, H-24), 4.19 (d, J = 2.3 Hz, 1H, H-25); 13C NMR
(75 MHz, CDCl3): 16.1, 22.6, 24.7, 26.9, 29.8, 31.4, 32.6, 34.0,
34.7, 35.2, 36.9, 39.8, 42.1, 43.7, 46.5, 49.7, 52.0, 54.6, 56.3, 63.7,
67.1, 72.9, 73.2, 75.8, 76.3, 77.6, 78.8. HRMS (EI) for C27H42O5
[M+] calcd 430.3032 found 446.3036.
(92%). Oil. IR (neat) 3429, 2950, 1606, 1089 cmÀ1
;
1H NMR
(300 MHz, CDCl3): 0.76 (s, 3H, H-18), 1.01 (d, J = 6.4, 3H, H-21),
1.07 (s, 3H, H-19), 2.84 (m, 1H, H-3), 3.29 (m, 1H, H-7), 4.15 (m,
2H, H-12), 4.29 (m, 4H, OCH2CH2N), 4.64 (s, 2H, H-25), 7.58 (s,
1H, CH@); 13C NMR (75 MHz, CDCl3): 18.3, 21.9, 24.6, 27.5, 30.8,
32.1, 33.7, 34.2, 36.3, 36.7, 37.1, 38.4, 39.8, 40.7, 43.9, 47.2, 51.6,
53.2, 57.2, 61.4, 62.6, 66.3, 67.1, 67.9, 69.8, 71.7, 78.2, 120.9,
142.6. HRMS (EI) for C29H49N3O5 [M+] calcd 519.3672 found
519.3676.
2.15. 3
yne (16)
a,7,8a,12a-Tetrahydroxy-7,8-seco-5b-cholan-24-oxyprop-1-
2.12. Propionyl ether of 3a,7a,12a-trihydroxy-5b-cholane (13)
A flask equipped with a magnetic stirring bar, an argon outlet
and a condenser was charged with NaBH4 (90 mg, 0.40 mmol)
and anhydr. THF (7 mL)–diglyme (3 mL) under argon. The solution
was cooled at 0 °C and then a solution composed of boron trifluor-
ide etherate (0.42 g, 3 mmol), ester 2 (0.18 mmol) and anhydr. THF
(5 mL) was added. After completion of the reaction (TLC), it was
quenched by addition of 2 N hydrochloric acid (1 mL) and water
(10 mL), the product was extracted with ether (3 Â 20 mL). The ex-
tracts were dried over MgSO4, filtered and then concentrated under
vacuum. The residue was chromatographed on silica gel (Et2O–
petroleum ether 1:1) to afford 40 mg (48%) of derivative 13 as an
A solution of propargyl ether 15 (1 g, 2.24 mmol) in dry ether
(10 mL) was added in one portion to a suspension of LiAlH4
(0.25 g, 6.73 mmol) in dry ether (20 mL) at room temperature.
After 1 h the reaction was quenched with H2O and EtOAc. The
aqueous layer was acidified to pH 2 with diluted HCl, and layers
were separated. The aqueous layer was further extracted with
EtOAc (3 Â 50 mL), and the combined organic layers were dried
over anhydrous MgSO4 and evaporated to dryness. The crude prod-
uct was purified by flash chromatography on silica gel (CH2Cl2/
MeOH: 9/1) to afford 0.78 g of pure tetraol 16 (78%) as an oil. IR
(neat) 3418, 2976, 1606 cmÀ1 1H NMR (300 MHz, CDCl3): 0.62
;
oil. IR (neat) 2981, 1370, 1048 cmÀ1 1H NMR (300 MHz, CDCl3):
;
(s, 3H, H-18), 0.84 (d, J = 6.4 Hz, 3H, H-21), 0.92 (s, 3H, H-19),
2.62 (t, J = 2.3 Hz, 1H, H-27), 3.34 (m, 1H, H-8), 3.52 (m, 2H, H-3
and H-12), 3.76 (m, 1H, H-7), 3.85 (m, 2H, H-24), 4.58 (d,
J = 2.4 Hz, 1H, H-25); 13C NMR (75 MHz, CDCl3): 15.9, 21.7, 22.4,
27.6, 29.3, 30.8, 31.3, 32.4, 33.6, 35.1, 36.9, 37.3, 38.2, 38.7, 42.1,
49.9, 53.1, 54.6, 56.3, 64.6, 68.4, 71.5, 72.0, 73.0, 73.6, 76.7, 78.9.
HRMS (EI) for C27H46O5 [M+] calcd 450.3345 found 446.3349.
0.72 (s, 3H, H-18), 1.01 (d, J = 6.4 Hz, 3H, H-21), 1.16 (s, 3H, H-
19), 2.52 (t, J = 2.4 Hz, 1H, H-27), 2.84 (m, 1H, H-7), 2.89 (m, 1H,
H-3), 3.38 (m, 1H, H-12), 3.52 (m, 1H, H-24), 4.13 (d, J = 2.2 Hz,
1H, H-25); 13C NMR (75 MHz, CDCl3): 17.6, 20.5, 24.7, 27.3, 29.6,
30.7, 31.4, 34.3, 34.6, 35.1, 36.3, 37.2, 41.6, 44.4, 46.8, 49.1, 50.7,
54.4, 57.5, 63.1, 68.6, 72.4, 74.7, 76.2, 77.4, 78.7, 79.2. HRMS (EI)
for C27H44O4 [M+] calcd 432.324 found 432.3243.
2.16. Halogenated precursor (17)
2.13. Propionyl ether of 3
a
,12
a
-dihydroxy-7-oxo-5b-cholane (14)
Compound 16 (90 mg, 0.2 mmol) was dissolved in toluene
(10 mL). To the homogenous solution CaH2 (82.3 mg, 1.96 mmol),
benzyltriethylammonium chloride (4.5 mg, 0.02 mmol) and chlo-
roacetic chloride (0.054 mL, 0.67 mmol) were added. The suspen-
sion was refluxed for 3 h. Then it was cooled to room
temperature and filtered. The filtrate was diluted with toluene
(30 mL) and washed with water solution of NaHCO3 (5%,
3 Â 15 mL), brine (3 Â 15 mL), water (2 Â 20 mL) and dried over
MgSO4. The solvent was evaporated under reduced pressure and
obtained crude product was purified by column chromatography
(hexane/AcOEt 6:1) to give secosteroidal derivative 17 (75 mg,
Steroid 13 (3 g, 6.94 mmol) was added to a solution of NaHCO3
(120 mL, 0.372 M) warmed at about 60 °C until the solid was
completely dissolved. After cooling to room temperature, NBS
(3.27 g, 18.37 mmol) was added and the resulting mixture was
stirred for 17 h at room temperature and for 2 h at 80–85 °C, then
allowed to cool to room temperature. The mixture was acidified
with aqueous HCl (6 M, 100 mL): the yellow precipitate was iso-
lated by filtration and washed with water, vigorously scratching.
The product was dissolved in acetone and dried over anhydrous
Na2SO4; the solvent was removed under reduced pressure afford-
72%) as yellow oil. IR (neat) 3416, 3290, 2940, 2125,
a
ing the crude product 14 (2.85 g, 95%). IR (neat) 2961, 1145 cmÀ1
;
1718 cmÀ1 1H NMR (300 MHz, CDCl3): 0.64 (s, 3H, H-18), 0.88
;
1H NMR (300 MHz, CDCl3): 0.68 (s, 3H, H-18), 0.99 (d, J = 6.4 Hz,
3H, H-21), 1.12 (s, 3H, H-19), 2.51 (t, J = 2.4 Hz, 1H, H-27), 2.92
(m, 1H, H-3), 3.46 (m, 1H, H-12), 3.52 (m, 1H, H-24), 4.24 (d,
J = 2.3 Hz, 1H, H-25); 13C NMR (75 MHz, CDCl3): 16.9, 21.3, 24.4,
27.6, 29.1, 31.3, 32.4, 33.3, 34.9, 35.6, 36.7, 37.8, 42.3, 44.2,
46.6, 49.3, 51.2, 54.6, 56.9, 64.4, 67.4, 73.1, 74.6, 76.4, 77.1,
78.2, 78.9. HRMS (EI) for C27H42O4 [M+] calcd 430.3083 found
430.3087.
(d, J = 6.4 Hz, 3H, H-21), 1.12 (s, 3H, H-19), 2.54 (t, J = 2.2 Hz, 1H,
H-27), 3.59 (m, 1H, H-8), 3.72 (m, 2H, H-3 and H-12), 3.87 (m,
1H, H-7), 3.93 (m, 2H, H-24), 4.36 (d, J = 2.3 Hz, 1H, H-25), 4.48
(s, 2H, CH2Cl); 13C NMR (75 MHz, CDCl3): 14.2, 19.8, 21.5, 22.7,
27.4, 29.5, 30.7, 31.9, 33.8, 35.4, 36.3, 37.4, 38.7, 39.8, 40.3, 40.8,
43.4, 48.6, 50.9, 52.0, 62.6, 65.6, 69.7, 69.9, 73.1, 73.7, 76.6, 78.9,
166.0. HRMS (EI) for C29H47ClO6 [M+] calcd 526.3061 found
526.3065.

106
M. Ibrahim-Ouali, K. Hamze / Steroids 80 (2014) 102–110
N
N
O
N
O
H
HO
O
HO
OH
H
H
OH
HO
HO
OH
HO
H
H
1
H
O
N
OH
HO
H
N
N
O
Scheme 2. Retrosynthetic pathway.
2.17. Azido precursor (18)
2.19. Macrocyle (20)
Chloro derivative 17 (274 mg, 0.52 mmol) was dissolved in dry
DMF (8 mL). To the solution sodium azide (201.5 mg, 3.1 mmol)
was added. The reaction mixture was heated at 60 °C for 24 h. Then
the mixture was poured onto crushed ice and extracted with
AcOEt. Organic layer was washed with water solution of NaHCO3
(5%, 3 Â 15 mL), brine (3 Â 15 mL), water (2 Â 20 mL) and dried
over MgSO4. The solvent was evaporated under reduced pressure
and obtained crude product was purified by column chromatogra-
phy (hexane/AcOEt 5:1) to give secosteroidal derivative 18
(188 mg, 68%) as a colourless oil. IR (neat) 3288, 2935, 2126,
A flask equipped with a magnetic stirring bar, an argon outlet
and a condenser was charged with NaBH4 (90 mg, 0.40 mmol)
and anhydr. THF (7 mL)–diglyme (3 mL) under argon. The solution
was cooled at 0 °C and then a solution composed of boron trifluor-
ide etherate (0.42 g, 3 mmol), macrocycle 10 (0.18 mmol) and
anhydr. THF (5 mL) was added. After completion of the reaction
(TLC), it was quenched by addition of 2 N hydrochloric acid
(1 mL) and water (10 mL), the product was extracted with ether
(3 Â 20 mL). The extracts were dried over MgSO4, filtered and then
concentrated under vacuum. The residue was chromatographed on
silica gel (Et2O–petroleum ether 1:1). IR (neat) 2951, 1175,
1720 cmÀ1 1H NMR (300 MHz, CDCl3): 0.66 (s, 3H, H-18), 0.83
;
(d, J = 6.4 Hz, 3H, H-21), 1.08 (s, 3H, H-19), 2.59 (t, J = 2.1 Hz, 1H,
H-27), 3.49 (m, 1H, CH2N3), 3.54 (m, 1H, H-8), 3.68 (m, 2H, H-3
and H-12), 3.82 (m, 1H, H-7), 3.97 (m, 2H, H-24), 4.28 (d,
J = 2.3 Hz, 1H, H-25); 13C NMR (75 MHz, CDCl3): 14.6, 18.9, 21.3,
23.1, 26.7, 29.3, 29.8, 30.4, 31.6, 35.7, 36.0, 36.4, 38.9, 39.6, 40.7,
41.6, 43.7, 49.6, 51.2, 52.7, 63.0, 65.1, 69.6, 70.1, 72.9, 73.4, 76.2,
78.6, 169.8. HRMS (EI) for C29H47N3O6 [M+] calcd 533.3465 found
533.3468.
1096 cmÀ1 1H NMR (300 MHz, CDCl3): 0.76 (s, 3H, H-18), 1.04
;
(d, J = 6.4 Hz, 3H, H-21), 1.12 (s, 3H, H-19), 3.46 (m, 1H, H-8),
3.58 (m, 2H, H-3 and H-7), 3.77 (m, 1H, H-12), 3.86 (m, 2H, H-
24), 4.02 (m, 4H, OCH2–CH2N), 5.06 (s, 2H, H-25), 7.54 (s, 1H,
CH@); 13C NMR (75 MHz, CDCl3): 14.5, 19.2, 21.9, 23.1, 27.3,
29.4, 30.4, 30.7, 32.1, 33.9, 36.7, 37.5, 38.4, 39.5, 41.3, 42.7, 44.1,
47.9, 51.7, 54.6, 65.2, 67.4, 70.3, 71.7, 73.6, 74.2, 76.8, 121.4,
142.9. HRMS (EI) for C29H49N3O5 [M+] calcd 519.3672 found
519.3676.
2.18. Macrocyle (19)
3. Results and discussion
A
mixture of the steroidal azide (105 mg, 0.2 mmol),
CuSO4Á5H2O (0.03 mmol, 7.5 mg), sodium ascorbate (0.076 mmol,
15 mg), DMF (2 mL) and water (2 mL) was stirred under argon at
room temperature for 12 h. Then, brine (3 mL) was added and
the mixture extracted with CH2Cl2 (3 Â 5 mL). The organic layers
were combined, washed with brine (3 mL) and dried over MgSO4.
The solvent was removed under vacuum and the product was
purified by column chromatography (hexane/AcOEt: 1/1) to afford
the desired secosteroidal macrocycle (65 mg, 62%) as an oil. IR
Our interest in secosteroidal molecules prompted us to look
into the possibilities of functionalizing the secosteroidal structures
with azides and alkynes for synthesizing macrocycles with 1,2,3-
triazole modifications. Our approach relies on a sequential ring-
expansion/ring-opening and on a ‘click reaction’ that allows the
construction of triazoles. Indeed, the copper(I)-catalysis for the
regioselective cycloaddition of terminal alkynes and azides origi-
nally developed by Sharpless and co-workers [34] and Meldal
and co-workers [35] has become the most useful, mild an efficient
process to produce exclusively the 1,4-disubstituted triazoles.
These latter are very stable to hydrolysis, reductive and oxidative
conditions and metabolic degradation. Moreover, 1,2,3-triazoles
show the ability to participate in hydrogen bonds and dipole inter-
actions [36–38].
(neat) 3302, 1738 cmÀ1 1H NMR (300 MHz, CDCl3): 0.78 (s, 3H,
;
H-18), 1.01 (d, J = 6.4 Hz, 3H, H-21), 1.16 (s, 3H, H-19), 3.48 (m,
1H, H-8), 3.51 (m, 1H, H-3), 3.82 (m, 1H, H-12), 3.88 (m, 2H,
H-24), 4.15 (m, 2H, H-7), 5.12 (s, 2H, H-25), 5.18 (s, 2H, CH2N),
7.62 (s, 1H, CH@); 13C NMR (75 MHz, CDCl3): 13.7, 18.8, 21.7,
22.4, 26.6, 29.1, 29.9, 30.1, 31.7, 34.3, 36.3, 37.4, 38.8, 39.2, 40.1,
42.5, 43.7, 47.4, 52.0, 54.1, 65.4, 70.1, 70.6, 73.2, 74.7, 76.3,
Two syntheses have been envisaged (Schemes 2 and 3) and in
the two cases, cholic acid 1, a commercial bile acid both inexpen-
sive and readily available, was chosen as starting material.
121.8, 143.6, 170.2. HRMS (EI) for
533.3465 found 533.3468.
C
29H47N3O6 [M+] calcd

M. Ibrahim-Ouali, K. Hamze / Steroids 80 (2014) 102–110
107
O
O
HO
H
HO
OR
O
H
b
c
H
H
H
H
HO
OH
MeO
OMe
H
H
1
2
R = H
R = CH2C CH
3
a
HO
H
O
H
O
O
d
e
H
H
H
H
MeO
OMe
MeO
OMe
H
H
5
4
OH
O
O
O
HO
O
H
g
f
H
H
H
H
MeO
OMe
MeO
OMe
H
H
6
7
N
N
N
N
N
O
O
O
R1
O
N
O
HO
O
O
O
HO
HO
i
j
H
H
H
H
OMe
H
H
OMe
R2O
OR2
MeO
MeO
H
H
H
8 R1 = Cl
9 R1 = N3
11 R2 = Me
12 R2 = H
10
h
k
Reaction conditions : (a) propargyl bromide, CH2Cl2, DCC, DMAP, r.t.,12 h, 75%; (b) CH3I, NaH, THF, r.t., 86%;
(c) NaBH4, BF3.Et2O, THF-diglyme, 0 °C, 4 h, 56%; (d) PCC, MW, 5 min, 68%; (e) m-CPBA, PTSA, CH2Cl2, r.t.,
24 h, 96%; (f) LiAlH4, THF, 0 °C to r.t., 12 h, 85%; (g) ClCH2COCl, CaH2, BnEt3N+Cl-, toluene, Δ, 3 h, 70%;
(h) NaN3, DMF, 60 °C, 24 h, 62%; (i) CuSO4.5H2O, sodium ascorbate, DMF/H2O, r.t., 12 h, 66%;
(j) NaBH4, BF3.Et2O, THF-diglyme, 0 °C, 4 h, 44%; (k) ISi(CH3)3, CHCl3, r.t., 24 h, 90%.
Scheme 3. Synthesis of a steroidal macrocycle 12 from cholic acid through eleven steps sequence.
Firstly, we turned our attention to the synthesis of 12,13-secos-
teroidal macrocycles matching a cis A/B ring junction and a 1,2,3-
triazole ring (Scheme 3). The key reactions leading to these new
secosteroids are depicted in Scheme 1. First, simple esterification
of cholic acid 1 led to propargyl cholate 2 [39], which was methyl-
ated with methyl iodide–sodium hydride in THF affording propar-
lyme–tetrahydrofuran at 0 °C during 4 h. Thus, reduction according
to the Pettit and Piatak procedure [40], afforded the expected ether
derivative 4 in a satisfactory yield (56%).
Microwave (MW) [41] irradiation of 4 with pyridinium chloro-
chromate furnished ketone 5 very quickly, in a few minutes, and in
68% yield. Baeyer–Villiger oxidation of ketocholane 5 led to lactone
6 as the single regioisomer, as a result of a higher migration apti-
tude of the quaternary C-13 compared to the secondary C-11. Next,
the reduction of the lactone moiety on ring C of 6 using lithium
aluminium hydride (LAH) afforded the diprotected tetrahydroxys-
ecocholane 7 in 85% yield.
gyl 3a,7a-dimethoxy cholate 3 in a yield of 86%. Simultaneous
protection of the secondary hydroxyl groups at C-3 and C-7 was
needed prior to the reductive opening of the lactone ring. In the
following step, we reduced the ester function of the lateral chain
of 3, using sodium borohydride and boron trifluoride, in dig-

108
M. Ibrahim-Ouali, K. Hamze / Steroids 80 (2014) 102–110
Table 1
Next, we proceeded to the installation of the azide moiety
CuAAC reaction of secosteroid 9 under different conditions.a
required for the intramolecular 1,3-dipolar cycloaddition. Indeed,
the key step of the synthesis is the construction of the macrocycle
using the ‘click reaction’ [34]. Two steps were necessary: chloro
derivative 8 was easily obtained from ester 7 in high yield by
reaction with chloroacetyl chloride in the presence of CaH2 and
triethylbenzylammonium chloride. This latter was transformed
into the corresponding azide 9 via a substitution reaction carried
out in DMF in the presence of NaN3. The 1H NMR spectrum showed
a signal at 3.51 ppm protons of the –CH2–N3 group.
Entry Catalyst Additive
Solvent
Temp (°C) 10: Yieldc (%)
1
2
3
4
5
6
7
8
CuSO4
CuSO4
CuSO4
CuSO4
CuSO4
CuI
Na-ascorbate tBuOH/H2O
Na-ascorbate iPrOH/H2O
Na-ascorbate CH2Cl2/H2O rt
rt
rt
18
23
52
66
15
26
19
16
Na-ascorbate DMF/H2O
Na-ascorbate DMSO/H2O
rt
rt
rt
rt
rt
DIPEAb
DIPEA
DIPEA
CH3CN
THF
DIPEA
CuI
CuI
In the cycloaddition reaction, the catalytically active species is a
Cu(I) complex. Although various Cu(I) salts and complexes can
efficiently be used as catalyst, the simplest catalytic consists of
CuSO4 and sodium ascorbate. The catalytically active Cu(I) species
a
b
c
Reaction conditions: 9/Cu = 0.2 mmol/0.03 mmol in 4 mL solvent, 12 h.
DIPEA: N,N-diisopropylethylamine.
All reactions were carried out for 12 h. All yields are given for isolated products
after column chromatography.
O
O
HO
H
HO
OH
O
H
a
b
H
H
H
H
HO
OH
HO
OH
H
H
1
2
HO
H
HO
H
O
O
c
d
H
H
O
H
H
HO
HO
OH
H
H
13
14
O
HO
HO
H
O
H
H
H
H
e
f
O
OH
OH
HO
HO
H
O
15
16
HO
HO
H
H
H
H
O
O
h
g
OH
OH
O
HO
O
HO
N3
Cl
O
O
18
17
HO
HO
H
H
H
O
H
O
O
N
i
OH
OH
HO
HO
H
H
N
N
N
N
N
O
O
19
20
Reagents and conditions: (a) propargyl bromide, CH2Cl2, DCC, DMAP, r.t.,12 h, 75%; (b) NaBH4,
BF3.Et2O, THF-diglyme, 0 °C, 6 h, 48%; (c) NBS, H2O, NaHCO3, 12 h at rt then 2 h at 80-85 °C, 95%;
(d) m-CPBA, PTSA, CH2Cl2, rt, 12 h, 76%; (e) LiAlH4, Et2O, 0 °C at rt, 12 h, 78%; (f) ClCH2COCl,
CaH2, BnEt3N+Cl-, toluene, Δ, 3 h, 72%; (g) NaN3, DMF, r.t., 12 h, 68%; (h) CuSO4.5H2O,
sodium ascorbate, DMF/H2O, 60 °C, 24 h, 62%; (i) NaBH4, THF-diglyme, BF3.Et2O, 0 °C at rt, 12 h, 52%.
Scheme 4. Synthesis of a steroidal macrocycle 20 from cholic acid through nine steps sequence.

M. Ibrahim-Ouali, K. Hamze / Steroids 80 (2014) 102–110
109
Table 2
ative 14 was subjected to the Baeyer–Villiger oxidation. As ex-
pected, this reaction furnished exclusively regioisomer 15, as a
result of the favoured migration of the tertiary C-8 compared to
the secondary C-6. In the next step, the reductive opening of the
lactone ring was done with lithium aluminium hydride in diethyl
ether and led to the secocholane 16 in a 72% yield (over two steps).
The chlorine in alkyne 16 was subsequently replaced by an azide
group by treatment with sodium azide in DMF. The corresponding
azide 17 was then isolated in 68% yield and confirmed by 1H NMR
spectroscopy which showed a characteristic signal at 3.58 ppm as-
signed to the –CH2–N3 group. Freshly obtained compound 17 was
used as a substrate in the ‘click reaction’.
Here too, in order to get the best reaction conditions for the 1,3-
dipolar cycloaddition, we undertook several attempts by changing
the solvent and the catalyst. The results were reported in Table 2.
It is worth pointing out similar results with the work we de-
scribed above for the synthesis of 12,13-secosteroidal macrocycles.
Indeed, the use of Cu (I) precursor was not very efficient (Table 2,
entries 6–8), in the other hand the system CuSO4 + Na-ascorbate
used in DMF/H2O as solvent at room temperature led to the cycli-
sation of 18 in a good yield (entry 4). And here too, the influence of
the temperature on the reaction appeared to be much less
important.
The new macrocycle 19 was completely characterized by NMR
(the 1H NMR spectrum of 19 showed a characteristic singlet at
7.62 ppm assigned to the triazole ring) and mass spectroscopic
methods (HRMS calcd for C29H4N3O6 533.3465, found 533.3468).
Finally, in order to obtain the ether-linked macrocycle 20, the
ester function of 19 was then reduced using sodium borohydride
and boron trifluoride, in diglyme–tetrahydrofuran at 0 °C during
4 h. The expected ether derivative 20 was isolated in a satisfactory
yield (48%).
In summary, we have developed a simple synthetic approach
for the synthesis of a novel class of secosteroidal triazoles via intra-
molecular 1,3-dipolar cycloaddition. These syntheses of 7,8- and
12,13-secosteroidal macrocycles have been accomplished in eleven
and nine steps respectively, starting from commercially available
cholic acid. Interesting is to note that, in one step, a macrocycle
and a new function were introduced efficiently on the steroidal
skeleton. Further studies to broaden the scope towards the synthe-
sis of novel biologically potential compounds are under investiga-
tion in our laboratory and will be reported in due course.
CuAAC reaction of secosteroid 18 under different conditions.a
Entry Catalyst Additive
Solvent
Temp (°C) 19: Yieldc (%)
1
2
3
4
5
6
7
8
CuSO4
CuSO4
CuSO4
CuSO4
CuSO4
CuI
Na-ascorbate tBuOH/H2O
Na-ascorbate iPrOH/H2O
Na-ascorbate CH2Cl2/H2O rt
rt
rt
12
18
48
62
21
22
10
14
Na-ascorbate DMF/H2O
Na-ascorbate DMSO/H2O
rt
rt
rt
rt
rt
DIPEAb
DIPEA
DIPEA
CH3CN
THF
DIPEA
CuI
CuI
a
b
c
Reaction conditions: 18/Cu = 0.2 mmol/0.03 mmol in 4 mL solvent, 12 h.
DIPEA: N,N-diisopropylethylamine.
All reactions were carried out for 12 h. All yields are given for isolated products
after column chromatography.
is formed in situ from the Cu(II) salt in the presence of the
ascorbate as the reducing agent. In this case, it is not necessary
to use absolutely oxygen-free conditions and the reaction usually
takes place smoothly at atmospheric pressure, at room tempera-
ture in an organic solvent/water mixture [34].
Firstly, the ‘click reaction’ of 9 was accomplished in the
presence of CuSO4Á5H2O and sodium ascorbate, in a mixture
tBuOH/H2O. The desired macrocycle 10 was isolated as the sole
product in a fair yield (18%). So, in order to get the best reaction
conditions for the 1,3-dipolar cycloaddition, we undertook several
attempts by changing the solvent and the catalyst. The results were
reported in Table 1.
The activities of CuSO4 + Na-ascorbate (entries 1–5) and
CuI + base catalyst systems (entries 6–8), commonly used for
similar reactions, were compared. The application of the Cu(I)
precursor was found to be less efficient. Fair yields were observed
for 10 (entries 6–8).
As reported in Table 1, the cycloaddition was found to be
efficient in
a solvent system of DMF/H2O to produce the
macrocycle 10 in 66% yield. The progress of the reaction was found
to be slow and took 12 h to reach completion. Otherwise, the new
triazole is formed in a completely regioselective manner.
Moreover, investigation of the temperature effects on the
reaction revealed that raising the temperature had no significant
influence on the yield although the reaction time could be
decreased to six hours.
The structure of the macrocycle compound 10 was determined
by a series of 1D NMR, COSY and NOESY experiments (400 MHz),
and confirmed by the (+)-HRESI mass spectra of the speudomolec-
ular ion [M+H]+ at m/z 561.3782, corresponding to the molecular
formula C31H51N3O6.
In the following step, in order to obtain ether-linked macrocycle
11 (Scheme 3), we reduced the ester function of 10, using sodium
borohydride and boron trifluoride, in diglyme-tetrahydrofuran at
0 °C during 4 h. Thus, the expected macrocycle derivative 11 was
isolated in a satisfactory yield (44%).
Acknowledgments
This work has been financially supported by the CNRS and the
Ministère de l’Enseignement Supérieur et de la Recherche.
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