3α-fluoro analogues of "allopregnanolone" and their binding to GABAA receptors

Article abstract of DOI:10.1135/cccc20020030

(Diethylamino)sulfur trifluoride (DAST) was used for the preparation of 3α-fluorides (e.g., 3α-fluoro-5α-pregnane-12,20-dione, 3α-fluoro-16α-[(methoxycarbonyl)methyl]-5α-pregnan-20-one, methyl 3α-fluoro-5α-androstane-17β-carboxylate, 3α-fluoro-5β-pregnan-

Full text of DOI:10.1135/cccc20020030

30
Slavíková et al.:
3α-FLUORO ANALOGUES OF “ALLOPREGNANOLONE”
AND THEIR BINDING TO GABAA RECEPTORS+
1,
2
3
Barbora SLAVÍKOVÁ *, Alexander KASAL , Hana CHODOUNSKÁ
4
and Zdena KRIŠTOFÍKOVÁ
Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic,
1
Flemingovo nám. 2, 166 10 Prague 6, Czech Republic; e-mail: barbora@uochb.cas.cz,
2
3
4
kasal@uochb.cas.cz, hchod@uochb.cas.cz, kristofikova@pcp.lf3.cuni.cz
Received Septem ber 21, 2001
Accepted Jan uary 8, 2002
Dedicated to the memory of late Dr Václav Černý.
(Dieth ylam in o)sulfur trifluoride (DAST) was used for th e preparation of 3α-fluorides (e.g.,
3α-fluoro-5α-pregn an e-12,20-dion e, 3α-fluoro-16α-[(m eth oxycarbon yl)m eth yl]-5α-pregn an -
20-on e, m eth yl 3α-fluoro-5α-an drostan e-17β-carboxylate, 3α-fluoro-5β-pregn an -20-on e) from
th e correspon din g 3β-alcoh ols an d for th e preparation of 3,3-difluorides from 3-keton es (e.g.,
3,3-difluoro-5α-pregn an -20-on e). Boron trifluoride eth erate was used for th e con version of
an epoxide in to 3α-fluoro-2β-h ydroxy-5α-pregn an -20-on e. Th e in vitro bin din g of th e 3α-flu-
orides an d th e correspon din g 3α-alcoh ols to th e GABAA receptor was establish ed usin g
[3H]m uscim ol an d [35S]-tert-butylbicyclo[2.2.2]ph osph oroth ion ate as ligan ds.
Keyw ord s: Allopregn an olon e; Epalon ; Neuroactive steroids; Fluorosteroids; Fluorin ation ;
1H NMR spectroscopy.
Com poun ds wh ich positively m odulate th e effects of γ-am in obutyric acid
(GABA) – on e of th e n eurotran sm itters affectin g an xiety, pain , in som n ia
an d drug depen dan ce – h ave a great th erapeutic poten tial. On e receptor of
γ-am in obutyric acid (GABAA receptor) is also m odulated by a few m etabo-
lites of progesteron e. Th e sim plest n eurosteroid – 3α-h ydroxy-5α-pregn an -
20-on e (1) – is kn own as “allopregn an olon e” or “epalon ”. It acts2–4 at con -
cen tration s 10 tim es h igh er th an ben zodiazepin es an d 100 tim es h igh er
th an barbiturates but, at larger con cen tration s, affects th e n euron s even in
th e absen ce of GABA. Furth er, it com bin es both th e effects of barbiturates
+ Part CDXIII in th e series On Steroids; Part CDXII see ref.1
Collect. Czech. Chem. Commun. (Vol. 67) (2002)
doi:10.1135/cccc20020030

3α-Fluoro Analogues of Allopregnanolone
31
an d ben zodiazepin es as far as th e frequen cy an d duration of th e ch loride
ion ch an n el open in g are con cern ed5. Yet th e steroidal partial agon ists of
GABAA receptors are bein g developed as an xiolytics because th ey sh ow
fewer an d less severe side effects com pared to con ven tion al ben zo-
diazepin es an d h ave a better selectivity for th e GABAA receptor subtypes.
Practical use of com poun d 1 h as been h am pered by its very fast m etabo-
lism an d low solubility in water an d, con sequen tly, various n ew an alogues
h ave been design ed in order to overcom e th ese drawbacks. Th us, com -
poun d 2 exerts a h igh GABA m odulatory activity in spite of h avin g th e
h ith erto essen tial 3α-h ydroxy group replaced with th e 3α-fluoro
substituen t6. Th e well-kn own stren gth of th e C–F bon d yielded a product
with a h igh m etabolic stability. However, th e presen ce of th e C–F bon d also
in creased th e lipoph ilicity of com poun d 2. Strivin g for an in creased h ydro-
ph ilicity of th e products, we m odified th e structure of fluoride 2 in various
position s (e.g., 2, 12, 16 an d 17), wh ere th e n ew substituen ts would n ot
jeopardize th e activities of th e products.
COCH3
COCH3
TsO
R
H
H
H
H
4
1, R = OH
2, R = F
(i)
COCH3
COCH3
HO
Br
(ii)
H
6
5
(iii)
COCH3
COCH3
HO
R
(iv)
O
H
3, R = F
8, R = OH
7
(i) Collidine, ∆; (ii) HClO4, N-Bromoacetamide; (iii) KOH; (iv) BF3·Et2O
SCHEME 1
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

32
Slavíková et al.:
Th e 2β-h ydroxy derivative 3 was prepared from 20-oxo-5α-pregn an -3β-yl
p-tosylate7 (4) via 5α-pregn -2-en -20-on e8 (5). Hypobrom ous acid addition
yielded diaxial brom oh ydrin 9 6 wh ich was con verted to epoxide9 7. Com -
poun d 7 afforded fluoroh ydrin 3 togeth er with 2β,3α-diol 8 upon treat-
m en t with boron trifluoride eth erate (Sch em e 1).
An oth er polar substituen t in troduced in to structure 2 was a 12-oxo
group. 3β-Hydroxy-5α-pregn an e-12,20-dion e10 (9), available from h eco-
gen in acetate10,11 (10), was treated with (dieth ylam in o)sulfur trifluoride
1
(DAST) to yield th e expected 3α-fluoro derivative 11; its H NMR spectrum
(a doublet of n arrow m ultiplets, J(3βH,3αF)gem = 49 Hz) proved th e presen ce
of th e fluorin e atom in an axial position . For th e sake of com parison , th e
3α-h ydroxy derivative 12 was also prepared by subjectin g com poun d 9 to
th e Mitsun obu reaction an d h ydrolysis of th e correspon din g 3α-form ate 13
(Sch em e 2).
O
O
O
COCH3
H
O
(i), (ii), (iii), (iv)
HO
H3CCOO
H
H
9
10
(v)
(vi)
O
O
COCH3
COCH3
RO
F
H
H
11
12, R = H
13, R = CHO
(i) Ac2O; (ii) CrO3, AcOH; (iii) KOH, t-BuOH; (iv) H2/Pd; (v) DAST;
(vi) PPh3, diethyl azodicarboxylate, HCOOH
SCHEME 2
Quatern ary am m on ium salts of carboxylic acids are m uch m ore polar
com poun ds. Th us, th e 16α-(m eth oxycarbon yl)m eth yl derivative12 14, pre-
viously used for th e preparation of quatern ary am m on ium salt12 15, was
treated with DAST to produce th e 3α-fluoro derivative 16. For th e GABAA
receptor tests, th e correspon din g free acid 17 an d its trieth ylam m on ium
salt 18 were prepared in a stan dard way.
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

3α-Fluoro Analogues of Allopregnanolone
33
Sim ilarly, m eth yl 3β-h ydroxyan drost-5-en e-17β-carboxylate13 (19) was
h ydrogen ated to afford th e 5α-dih ydro derivative13,14 20 wh ich was con -
verted in to th e 3α-fluoro ester 21, th e correspon din g free acid 22 an d its
salts 23 an d 24. Th e fluoro alcoh ol 25 was obtain ed by th e reduction of es-
ter 21 with lith ium alum in um h ydride. Oxidation of alcoh ol 25 with ch ro-
m ium trioxide yielded an oth er poten tial n euroactive steroid – th e fluoro
aldeh yde 26.
For th e purpose of com parison , a sim ilar sequen ce was carried out in th e
3α-h ydroxy series: th e kn own 15 3α-h ydroxy ester 27 was h ydrolyzed to th e
free acid16 28 an d n eutralized to yield salt 29. Th e h ydroxy acid 28 was
th en acetylated at th e 3-h ydroxyl, an d acylated at th e 17-carboxyl with
eth yl ch loroform ate; th e in term ediate m ixed an h ydride was reduced with
sodium boroh ydride to yield 3α-acetoxy-20-alcoh ol 30. Ch rom ium trioxide
oxidation an d h ydrolysis afforded 3α-acetoxy- an d 3α-h ydroxy aldeh ydes
31 an d 32 (ref.17), respectively (Sch em e 3).
Hogen kam p an d oth ers18 h ave sh own th at 3β-substituen ts, in troduced
in to th e structure of n eurosteroid 1, im prove th e an aesth etic properties of
such products. In th is con text, we were in terested in th e preparation an d
testin g of th e 3β-fluoro derivative of com poun d 2, i.e. th e 3,3-difluoro an a-
logue19 33. Th e target com poun d was produced from 20-h ydroxy-5α-
pregn an -3-on es20 34 an d 35. Th e 20-h ydroxy groups were protected by
ben zoylation , an d ben zoates21 36 an d 37 were treated with DAST at 80 °C
for 8 h . Difluoro ben zoates 38 an d 39 were h ydrolyzed with potassium h y-
droxide to alcoh ols 40 an d 41 wh ich were oxidized to difluoro keton e 33.
Th e an aesth etic properties of allopregn an olon e (1) are surpassed by its
5β-epim er 42 – an oth er n atural n eurosteroid. Th erefore, we decided to pre-
pare its 3α-fluoro an alogue, i.e. 3α-fluoro-5β-pregn an -20-on e (43). It was
produced by th e reaction of 3β-alcoh ol22 44 with DAST at room tem pera-
ture (Sch em e 4).
Th e bin din g of th e above 3α-h ydroxy- an d 3α-fluoro com poun ds to
GABAA receptors was tested in vitro usin g n eural m em bran es of m ale rat
brain s. Th e specific steroid bin din g was detected by th e in crease of th e spe-
cific [3H]m uscim ol an d decrease of th e specific [35S]-tert-butylbicyclo-
[2.2.2]ph osph oroth ion ate (TBPS) bin din g after application of th e tested
com poun ds. Th e results (see Tables I an d II) could be sum m arized as fol-
lows: (i) Th e im pact of th e substitution of fluorin e for th e 3α-h ydroxyl does
n ot follow a coh eren t lin e. In five cases (com poun ds 3, 11, 21, 24, 43), th e
m uscim ol bin din g of fluoro an alogues seem s to be stron gly reduced wh en
com pared with th e 3α-alcoh ols. Th ese data m ay be due to eith er th e in com -
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

34
Slavíková et al.:
patibility of th e substrates with th e GABAA receptor or due to th eir lower
solubility in th e testin g m edium caused by a h igh er lipoph ilicity of th e flu-
orides as com pared with th e correspon din g alcoh ols. Also, fluoride 2 seem s
to be sligh tly less active th an its h ydroxylic coun terpart, allopregn an olon e
(1), even th ough beh avioral tests with m ice sh ow an tiaggressive effects. On
th e oth er h an d, two fluoro com poun ds (18, 26) in crease th e m uscim ol
COCH3
COCH3
COO-Et3NH+
COOCH3
HO
HO
H
H
15
14
(i)
COCH3
COOCH3
COOCH3
R2
COOR
F
HO
H
16, R = CH3
17, R = H
18, R = Et3NH
19
(ii)
R
(i)
F
HO
H
H
20
21, R = COOCH3
22, R = COOH
23, R = COONa
24, R = COO-Et3NH+
25, R = CH2OH
26, R = CHO
(iii), (iv)
27, R1 = OH, R2 = COOCH3
28, R1 = OH, R2 = COOH
29, R1 = OH, R2 = COO-Et3NH+
30, R1 = OAc, R2 = CH2OH
31, R1 = OAc, R2 = CHO
32, R1 = OH, R2 = CHO
R1
H
(i) DAST; (ii) H2/Pd; (iii) DCC, CuCl, HCOOH; (iv) KOH
SCHEME 3
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

3α-Fluoro Analogues of Allopregnanolone
35
bin din g m ore profoun dly th at th e correspon din g 3α-alcoh ols 15 an d 32.
(ii) Modification of th e allopregn an olon e structure in position s oth er th an
3α leads to in creased bin din g of m uscim ol. However, sh ould a good posi-
tive m odulator of GABA pass both th e m uscim ol an d TBPS tests used, on ly
two com poun ds would be selected: 12-oxo-allopregn an olon e (12) an d a salt
of th e fluoro derivative (18). It is n oteworth y th at th e form er is a 3α-alco-
h ol an d th e latter is a 3α-fluoride.
RO
H
RO
H
(i)
F
O
F
H
H
38, R = Bz
40, R = H
34, R = H (20R)
35, R = H (20S)
36, R = Bz (20R)
37, R = Bz (20S)
(ii)
(i)
COCH3
H
OR
(ii)
F
F
H
F
F
H
39, R = Bz
41, R = H
33
COCH3
COCH3
(i)
F
HO
H
H
42, OH (3α)
44, OH (3β)
43
(i) DAST; (ii) CrO3, H2SO4
SCHEME 4
Of all th e above com poun ds, n o gen eral rule about th e 3α-fluoro an a-
logues of allopregn an olon e can be form ulated. In som e cases, th e 3α-fluoro
an alogue surpasses th e GABA-like activity of its 3α-alcoh ol, in oth er cases it
does n ot.
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

36
Slavíková et al.:
EXPERIMENTAL
Meltin g poin ts were determ in ed on a m eltin g poin t m icro apparatus Boetius (Germ an y) an d
are un corrected. An alytical sam ples were dried over ph osph orus pen toxide at 50 °C/100 Pa.
Optical rotation s were m easured in ch loroform ([α]D values are given in 10–1 deg cm 2 g–1).
IR spectra of ch loroform solution s were recorded on a Bruker IFS 88 spectrom eter, wave-
n um bers are given in cm –1. NMR spectra were m easured on a FT-NMR spectrom eter Varian
Un ity-200 (at 200 MHz) in CDCl3 with tetram eth ylsilan e as in tern al referen ce. Ch em ical
sh ifts are given in ppm (δ-scale), couplin g con stan ts an d width s of m ultiplets in Hz. Un less
oth erwise stated, th e data were in terpreted as th e first-order spectra. Th in -layer ch rom atogra-
ph y (TLC) was perform ed on silica gel (ICN Bioch em icals). Preparative TLC (PLC) was car-
TABLE I
Modulatory effect of 3α-h ydroxy (R = OH) an d 3α-fluoro (R = F) products on GABAA recep-
tors
[3H]-Muscim ol bin din g
Com poun d
R
EC50a, n M
Em axb, %
E100n Mc, %
1
OH
F
154.7
122.6
104.1
123.7
101.5
115.2
43.7
2
1 000.0
8
OH
F
166.3
186.3
d
d
3
12
11
15
18
27
21
29
24
32
26
33
42
43
OH
F
10.0
147.3
109.1
85.3
d
d
OH
F
116.2
99.4
126.2
192.8
103.8
154.6
178.3
67.4
OH
F
550
162
d
d
OH
F
500
144
126.5
71.8
d
d
d
d
OH
F
110.1
127.9
61.1
98.1
200.0
d
d
F
OH
F
633.3
145.8
110.5
78.9
d
d
a
b
Th e steroid con cen tration producin g a h alf-m axim al respon se.
Th e m axim al en h an ce-
c
d
m en t of th e bin din g. Related to th e DMSO bin din g. Not m easured due to low solubility
of th e com poun d.
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

3α-Fluoro Analogues of Allopregnanolone
37
ried out on 200 × 200 m m plates coated with a 0.7 m m th ick layer of th e sam e m aterial. For
colum n ch rom atograph y, 60–120 µm silica gel was used. Wh en ever aqueous solution s of h y-
droch loric acid, potassium h ydrogen carbon ate an d potassium carbon ate were used, th eir
con cen tration was always 5%. Before evaporation on a rotary evaporator in a vacuum (bath
tem perature 50 °C), solution s in organ ic solven ts were dried over an h ydrous sodium sulfate.
Receptor binding assay. Mem bran es23 were prein cubated at 37 °C for 10 m in in 50 m M
Tris-HCl buffer (pH 7.4) with or with out steroid. Th e m ixture was in cubated with
[3H]m uscim ol (5 n M) an d, after 10 m in , th e reaction was term in ated by a rapid vacuum fil-
tration th rough a Wh atm an GF/B glass-fiber filter. Non specific bin din g was determ in ed in
th e presen ce of 1 m M GABA.
TABLE II
Modulatory effect of 3α-h ydroxy (R = OH) an d 3α-fluoro (R = F) products on GABAA recep-
tors
[
35S]-TBPS bin din g
Im axb, %
Com poun d
R
IC50a, n M
80.0
I100n Mc, %
1
OH
F
79.0
56.2
90.2
2
50.0
17.0
d
d
8
OH
F
135.4
d
d
d
3
12
11
15
18
27
21
29
24
32
26
33
42
43
OH
F
50.0
43.0
53.1
d
d
d
OH
F
40.0
19.0
78.6
76.9
75.0
34.0
d
d
OH
F
96.6
d
d
d
d
d
d
d
d
d
d
d
d
d
OH
F
126.6
d
d
OH
F
111.9
d
F
OH
F
8.0
21.0
62.2
d
d
d
a
b
Th e steroid con cen tration producin g a h alf-m axim al in h ibition . Th e m axim al suppres-
c
d
sion of th e bin din g. Related to th e DMSO bin din g. Not determ in ed.
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

38
Slavíková et al.:
Prelim in ary experim en ts with 5 n M [3H]m uscim ol were carried out with 100 n M con cen -
tration of steroids (see Table I). Experim en ts with 2 n M [35S]TBPS were perform ed on ly with
th e 100 n M con cen tration of steroids (see Table II).
Gen eral Procedure for th e Con version of Alcoh ols to Fluorides
An azeotropic m ixture (10 m l) was distilled off from a solution of a steroidal alcoh ol
(1.57 m m ol) in dich lorom eth an e (20 m l). (Dieth ylam in o)sulfur trifluoride (DAST, 366 m g,
2.27 m m ol) was added to th e m ixture at room tem perature. Wh en th e reaction was com -
plete (TLC m on itorin g), th e m ixture was diluted with dich lorom eth an e (40 m l) an d wash ed
with th e potassium h ydrogen carbon ate solution an d water. After evaporation of th e solven t,
th e residue was separated by flash ch rom atograph y on a colum n of silica gel (50 g). Yields
varied from 30 to 50%.
5α-Pregn -2-en e-20-on e (5)
A solution of tosylate7 4 (1.10 g, 2.33 m m ol) in 2,4,6-trim eth ylpyridin e (11 m l) was h eated
to reflux for 4 h . Th e reaction m ixture was poured in to dilute h ydroch loric acid (10%,
35 m l) an d th e product was extracted with eth er. Th e extract was wash ed with water, th e
potassium h ydrogen carbon ate solution an d dried. After evaporation of th e solven t, an ad-
m ixture of 3-en e was rem oved by partial sulfation 24. Yield of olefin 5: 0.545 g (78%), m .p.
125–126 °C (m eth an ol, ref.8 gives 126–129 °C). 1H NMR: 0.61 s, 3 H (3 × H-18); 0.76 s, 3 H
(3 × H-19); 2.12 s, 3 H (3 × H-21); 5.31 m , 2 H, W1/2 = 4 (H-2 an d H-3).
3α-Brom o-2β-h ydroxy-5α-pregn an -20-on e (6)
Perch loric acid (1 N, 0.51 m l) was added to a solution of olefin 5 (690 m g, 2.3 m m ol) in
dioxan e (45 m l) at 15 °C upon stirrin g. N-Brom oacetam ide (317 m g, 2.1 m m ol) was added
in 6 portion s over 30 m in . After an addition al 30 m in , th e m ixture was quen ch ed by th e ad-
dition of a sodium h ydrogen sulfite solution (10%, 3.3 m l). After 18 h , a precipitate was col-
lected an d crystallized from m eth an ol. Yield: 730 m g (80%), m .p. 207–209 °C (ref.9 recorded
210.5–212 °C). 1H NMR: 0.61 s, 3 H (3 × H-18); 1.00 s, 3 H (3 × H-19); 2.12 s, 3 H (3 ×
H-21); 4.35 m , 1 H, W1/2 = 6 (H-2); 4.22 m , 1 H, W1/2 = 8 (H-3).
2β,3β-Epoxy-5α-pregn an -20-on e (7)
A solution of potassium h ydroxide (100 m g, 1.78 m m ol) in a m ixture of water (0.3 m l) an d
m eth an ol (1 m l) was added to a solution of brom oh ydrin 6 (350 m g, 0.88 m m ol) in m eth a-
n ol (40 m l). Th e reaction m ixture was h eated to reflux for 2 h . On addition of brin e, a pre-
cipitate was form ed. Th e solid was collected, wash ed with water an d dried. Crystallization
from m eth an ol gave 320 m g (73%) of com poun d 7, m .p. 173–175 °C (ref.9 recorded
174–175.5 °C). 1H NMR: 0.56 s, 3 H (3 × H-18); 0.81 s, 3 H (3 × H-19); 2.09 s, 3 H (3 ×
H-21); 3.13 m , 2 H, W1/2 = 16 (H-2, H-3); 2.49 t, 1 H, J = 9 (H-17).
3α-Fluoro-2β-h ydroxy-5α-pregn an -20-on e (3)
Boron trifluoride dieth yl eth erate (123 m g, 0.86 m m ol) was added to a solution of epoxy
com poun d 7 (70 m g, 0.22 m m ol) in a m ixture of toluen e (3.5 m l) an d eth er (3.5 m l). After
2 h , th e m ixture was wash ed with th e potassium carbon ate solution an d water, an d dried.
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

3α-Fluoro Analogues of Allopregnanolone
39
After evaporation of th e solven t, th e residue was applied on two preparative TLC plates
wh ich were developed with ligh t petroleum –eth yl acetate (8 : 2). Th e polar zon es yielded
26 m g (35%) of com poun d 3, m .p. 194–197 °C (aceton e–h eptan e), [α]D +98 (c 1.2). IR: 3 622
(OH), 1 697 (C=O), 1 030 (C–OH), 994 (C–F). 1H NMR: 0.61 s, 3 H (3 × H-18); 0.99 s, 3 H
(3 × H-19); 2.11 s, 3 H (3 × H-21); 2.53 t, 1 H, J = 9 (H-17); 4.10 m , 1 H, W1/2 = 15 (H-2);
4.61 dm , 1 H, J(F,H-3) = 46 (H-3). For C21H33FO2 (336.5) calculated: 74.96% C, 9.89% H;
foun d: 74.83% C, 9.78% H.
2β,3α-Dih ydroxy-5α-pregn an -20-on e (8)
Th e less polar zon es from th e preparative plates of th e above experim en t gave 31 m g (42%)
of com poun d 8, m .p. 212–219 °C (eth an ol), [α]D +67 (c 1.0). IR: 3 616, 3 390 (OH); 1 697
(C=O); 1 021, 1 003 (C–OH). 1H NMR: 0.61 s, 3 H (H-18); 1.01 s, 3 H (H-19); 2.12 s, 3 H
(H-21); 4.15 m , 2 H, W1/2 = 19 (H-2, H-3).
3β-Hydroxy-5α-pregn an e-12,20-dion e (9)
Hecogen in acetate (10) was con verted in to com poun d 9 accordin g to refs10,11, m .p. 193–
196 °C (ref.10 recorded 189–195 °C). IR: 3 610, 1 035 (OH); 1 694 (C=O); 1 385, 1 360 (CH3).
1H NMR: 0.90 s, 3 H (3 × H-18); 0.95 s, 3 H (3 × H-19); 2.26 s, 3 H (3 × H-21); 2.50 t, 1 H,
J = 13 (H-17); 3.31 t, 1 H, J = 9 (H-11β); 3.61 m , 1 H, W1/2 = 32 (H-3).
3α-Fluoro-5α-pregn an e-12,20-dion e (11)
Followin g th e gen eral procedure, alcoh ol 9 (100 m g, 0.3 m m ol) was treated with DAST
(97 m g, 0.60 m m ol) in dich lorom eth an e (1 m l) at room tem perature for 2 h . Ch rom atogra-
ph y was carried out usin g two preparative TLC plates (ligh t petroleum –eth er, 7 : 3). Yield of
11: 36 m g (36%), m .p. 146–149 °C (aceton e–h eptan e), [α]D +166 (c 1.1). IR: 1 702 (C=O),
992 (C–F). 1H NMR: 0.87 s, 3 H (3 × H-18); 0.95 s, 3 H (3 × H-19); 2.27 s, 3 H (3 × H-21);
2.48 t, 1 H, J = 13 (H-17); 3.32 t, 1 H, J = 9 (H-11β); 4.82 dm , 1 H, J(F,H-3) = 49 (H-3). For
C
21H31FO2 (334.5) calculated: 75.41% C, 9.34% H; foun d: 75.35% C, 9.26% H.
3α-Hydroxy-5α-pregn an e-12,20-dion e (12)
A solution of potassium h ydrogen carbon ate (50 m g, 0.50 m m ol) in water (1 m l) was added
to a solution of form ate 13 (96 m g, 0.27 m m ol) in m eth an ol (9 m l), an d th e reaction m ix-
ture was h eated to reflux for 10 m in . Th e solution was con cen trated to a quarter of its origi-
n al volum e, an d com poun d 12 (80 m g, 90%) precipitated upon th e addition of brin e (5 m l).
M.p. 199–201 °C an d 229–230 °C (aceton e–h eptan e, 71 m g, 80%), [α]D +170 (c 1.0).
1H NMR: 0.87 s, 3 H (3 × H-18); 0.95 s, 3 H (3 × H-19); 2.27 s, 3 H (3 × H-21); 2.46 t, 1 H,
J = 13 (H-17); 3.32 t, 1 H, J = 9 (H-11β); 4.07 m , 1 H, W1/2 = 7 (H-3). IR: 3 616, 3 482, 3 434,
3 390, 1 085 (OH); 1 702 (C=O); 1 383, 1 362 (CH3). For C21H32O3 (332.5) calculated:
75.86% C, 9.70% H; foun d: 75.86% C, 9.65% H.
12,20-Dioxo-5α-pregn an -3α-yl Form ate (13)
From a m ixture of com poun d 9 (120 m g, 0.36 m m ol) an d triph en ylph osph in e (300 m g,
1.14 m m ol) in ben zen e (10 m l) an d toluen e (20 m l), an azeotropic m ixture (10 m l) was dis-
tilled off. Th e flask was quickly (with in 3 m in ) cooled in ice-cool water an d 10 drops of di-
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

40
Slavíková et al.:
eth yl azodicarboxylate (1.44 m m ol) were dripped in . Th e yellow solution was stirred for
8 m in an d th en form ic acid (3 drops, 1.43 m m ol) was added. After 3 h , th e m ixture was
wash ed successively with th e solution of potassium h ydrogen carbon ate an d water, dried an d
evaporated. Th e residue was applied on th ree preparative TLC plates th at were developed
with a m ixture of ben zen e an d eth er (3 : 1). Th e m ajor ban d (RF 0.5) was eluted with eth er,
yieldin g 105 m g (81%) of form ate 13, m .p. 195–197 °C (aceton e), [α]D +178 (c 0.9). 1H NMR:
0.89 s, 3 H (3 × H-18); 0.95 s, 3 H (3 × H-19); 2.26 s, 3 H (3 × H-21); 2.50 t, 1 H, J = 13
(H-17); 3.32 t, 1 H, J = 9 (H-11β); 5.18 m , 1 H, W1/2 = 7 (H-3); 8.05 s, 1 H (CH=O). For
C
22H32O4 (360.5) calculated: 73.30% C, 8.95% H; foun d: 73.04% C, 9.01% H.
Meth yl (3α-Fluoro-20-oxo-5α-pregn an -16α-yl)acetate (16)
Followin g th e gen eral procedure, a solution of ester 14 (ref.12, 1.0 g, 2.55 m m ol) in dich loro-
m eth an e (20 m l) was treated with DAST for 18 h . Ch rom atograph y of th e product was car-
ried out on a colum n of silica gel (100 m l). Ligh t petroleum –eth er (9 : 1) eluted com poun d
16 (0.236 g, 23%), m .p. 140–142 °C (aceton e–h eptan e), [α]D +57 (c 1.3). IR: 1 731, 1 438,
1 161 (COOCH3); 1 701, 1 358 (CH3CO); 991 (C–F). 1H NMR: 0.63 s, 3 H (3 × H-18); 0.78 s,
3 H (3 × H-19); 2.12 s, 3 H (3 × H-21); 2.21 dd, 1 H, J = 7 an d J′ = 14 (H-16a1); 2.30 dd, 1 H,
J = 7 an d J′ = 14 (H-16a2); 2.39 d, 1 H, J = 9 (H-17); 3.62 s, 3 H (OCH3); 4.81 dm , 1 H,
J(F,H-3) = 49 (H-3). For C24H37FO3 (392.6) calculated: 73.43% C, 9.50% H; foun d: 73.27% C,
9.38% H.
(3α-Fluoro-20-oxo-5α-pregn an -16α-yl)acetic Acid (17)
Ester 16 (238 m g, 0.61 m m ol) was h ydrolyzed with a solution of h ydroch loric acid (17%,
4 m l) in aceton e (20 m l) at room tem perature. After 48 h , th e m ixture was con cen trated to a
quarter of its origin al volum e an d diluted with dich lorom eth an e (20 m l). Th e resultan t solu-
tion was wash ed with brin e an d dried. Evaporation of th e solven t an d crystallization of th e
residue from aceton e–h eptan e afforded acid 17 (141 m g, 61%), m .p. 183–185 °C, [α]D +69
(c 1.3). IR: 3 515, 1 743 (COOH); 984 (C–F). 1H NMR: 0.64 s, 3 H (3 × H-18); 0.78 s, 3 H (3 ×
H-19); 2.12 s, 3 H (3 × H-21); 2.30 d, 2 H, J = 8 (H-16a); 2.38 d, 1 H, J = 9 (H-17); 3.00 m ,
1 H, W1/2 = 24 (H-16); 4.81 dm , 1 H, J(F,H-3) = 48 (H-3). For C23H35FO3 (378.5) calculated:
72.98% C, 9.32% H; foun d: 72.84% C, 9.23% H.
Trieth ylam m on ium (3α-Fluoro-20-oxo-5α-pregn an -16α-yl)acetate (18)
A solution of carboxylic acid 17 (200 m g, 0.53 m m ol) in trieth ylam in e (16 m l) was h eated
to reflux for 20 m in . Th e solven t was evaporated an d th e residue crystallized from eth er at
–60 °C, yieldin g com poun d 18 (127 m g, 50%), m .p. >300 °C (decom p.). IR: 1 702 (C=O),
1 407 (COO–), 984 (C–F). 1H NMR: 0.64 s, 3 H (3 × H-18); 0.78 s, 3 H (3 × H-19); 1.24 t, 9 H,
J = 7 (3 × CH3-CH2); 2.12 s, 3 H (3 × H-21); 2.22 d, 2 H, J = 8 (2 × H-16a); 2.40 d, 1 H, J = 9
(H-17); 2.96 m , 1 H, W1/2 = 24 (H-16); 3.00 q, 6 H, J = 8 (3 × CH2-N); 4.81 dm , 1 H, J(F,H-3)
= 48 (H-3). For C29H50FNO3 (479.7) calculated: 72.61% C, 10.51% H, 2.92% N; foun d:
72.52% C, 10.38% H, 2.84% N.
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3α-Fluoro Analogues of Allopregnanolone
41
Meth yl 3β-Hydroxy-5α-an drostan e-17β-carboxylate (20)
Com poun d 20 was prepared by a palladium -catalyzed h ydrogen ation of m eth yl 3β-h ydroxy-
an drost-5-en e-17β-carboxylate (19; 10.0 g, 30.1 m m ol) in m eth an ol (400 m l) accordin g to
ref.14, m .p. 168–173 °C (m eth an ol, ref.13 gives 172 °C, ref.14 gives 168–171 °C). 1H NMR:
0.64 s, 3 H (3 × H-18); 0.81 s, 3 H (3 × H-19); 2.33 t, 1 H, J = 9 (H-17); 3.59 m , 1 H, W1/2
=
28 (H-3); 3.66 s, 3 H (OCH3).
Meth yl 3α-Fluoro-5α-an drostan e-17β-carboxylate (21)
Followin g th e gen eral procedure, alcoh ol 20 (1.0 g, 2.99 m m ol) was treated with DAST
(0.702 g, 4.36 m m ol) in dich lorom eth an e (20 m l) for 18 h . Th e product crystallized with out
ch rom atograph ic purification . Yield: 0.392 g (39%), m .p. 139–141 °C (ligh t petroleum ), [α]D
+50 (c 1.3). IR: 1 725, 1 198 (COO); 989 (C–F). 1H NMR: 0.65 s, 3 H (3 × H-18); 0.78 s, 3 H
(3 × H-19); 2.33 t, 1 H, J = 9 (H-17); 3.66 s, 3 H (OCH3); 4.81 dm , 1 H, J(F,H-3) = 49 (H-3).
For C21H33FO2 (336.5) calculated: 74.96% C, 9.89% H; foun d: 74.81% C, 9.70% H.
3α-Fluoro-5α-an drostan e-17β-carboxylic Acid (22)
A solution of potassium h ydroxide (570 m g, 10.18 m m ol) in water (1.5 m l) was added to a
solution of ester 21 (570 m g, 1.70 m m ol) in dioxan e (10.4 m l) an d th e m ixture was h eated
at reflux for 8 h . Th e m ixture was diluted with brin e (20 m l), acidified with dilute h ydro-
ch loric acid an d th e precipitate form ed was extracted with eth yl acetate. After rem ovin g th e
solven t, th e residue crystallized from aceton e–h eptan e yieldin g acid 22 (170 m g, 31%).
Ch rom atograph y of m oth er liquor on five preparative plates afforded an addition al crop
(340 m g, 62%) of com poun d 22, m .p. 230–231 °C, [α]D +27 (c 1.2). IR: 3 514, 1 732, 1 428
(COOH); 990 (C–F). 1H NMR: 0.72 s, 3 H (3 × H-18); 0.80 s, 3 H (3 × H-19); 2.40 t, 1 H, J = 9
(H-17); 4.81 dm , 1 H, J(F,H-3) = 49 (H-3). For C20H31FO2 (322.5) calculated: 74.50% C,
9.69% H; foun d: 74.46% C, 9.60% H.
Sodium 3α-Fluoro-5α-an drostan e-17β-carboxylate (23)
A solution of acid 22 (54 m g, 0.17 m m ol) in m eth an ol (1 m l) was treated with a m eth an olic
solution of sodium m eth oxide (0.87 M, 0.2 m l, 0.17 m m ol). After 1 h , th e solven t was evap-
orated an d th e residue was triturated with eth er. Th e m ixture was filtered, th e filtrate was
evaporated; th e residue (23; 52 m g, 90%) did n ot m elt below 300 °C, [α]D +36 (c 1.0,
CH3OH–CHCl3, 1 : 1). IR spectrum (KBr): 1 552, 1 414, 678, 655, 607 (COO–); 1 383 (CH3);
987 (C–F). 1H NMR (CDCl3 + CD3OD): 0.68 s, 3 H (3 × H-18); 0.78 s, 3 H (3 × H-19); 2.21 t,
1 H, J = 8.8 (H-17); 4.81 dm , 1 H, J(F,H-3) = 49 (H-3). For C20H30FNaO2 (344.4) calculated:
69.74% C, 8.78% H; foun d: 69.47% C, 8.51% H.
Trieth ylam m on ium 3α-Fluoro-5α-an drostan e-17β-carboxylate (24)
A solution of acid 22 (50 m g, 0.16 m m ol) in trieth ylam in e (4.0 m l, 28.7 m m ol) was h eated
to reflux for 20 m in . On coolin g, salt 24 crystallized from th e reaction m ixture. Yield: 51 m g
(78%), m .p. 243–254 °C, [α]D +34 (c 1.2). IR: 2 476 (Et3NH+); 1 700, 1 594 (COO–); 989
(C–F). 1H NMR: 0.71 s, 3 H (3 × H-18); 0.79 s, 3 H (3 × H-19); 1.16 t, 9 H, J = 7 (3 ×
CH3-CH2); 2.34 t, 1 H, J = 9 (H-17); 2.85 q, 6 H, J = 7 (3 × CH2-N); 4.81 dm , 1 H, J(F,H-3) =
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

42
Slavíková et al.:
49 (H-3). For C26H46FNO2 (423.7) calculated: 73.71% C, 10.94% H, 3.31% N; foun d:
73.48% C, 10.70% H, 3.09% N.
3α-Fluoro-21-n or-5α-pregn an -20-ol (25)
Com poun d 21 (60 m g, 0.18 m m ol) was reduced with lith ium alum in um h ydride (7.8 m g,
0.21 m m ol) in tetrah ydrofuran (0.5 m l) at room tem perature. After 24 h , th e excess reagen t
was decom posed with m oist eth er an d with a saturated aqueous solution of sodium sulfate.
Th e m ixture was saturated with an h ydrous sodium sulfate an d th e solution was filtered. On
rem oval of th e solven t from th e filtrate, com poun d 25 (45 m g, 82%) was obtain ed, m .p.
146–148 °C (aceton e–h eptan e), [α]D +8 (c 1.2). IR: 3 622, 3 457 (OH); 990 (C–F). 1H NMR:
0.64 s, 3 H (3 × H-18); 0.79 s, 3 H (3 × H-19); 3.54 dd, 1 H, J = 7 an d J′ = 10 (H-20a);
3.72 dd, 1 H, J = 7 an d J′ = 10 (H-20b); 4.81 dm , 1 H, J(F,H-3) = 49 (H-3). For C20H33FO
(308.5) calculated: 77.87% C, 10.78% H; foun d: 77.73% C, 10.71% H.
3α-Fluoro-21-n or-5α-pregn an -20-al (26)
Pyridin e (0.1 m l) was added dropwise at 0 °C in argon atm osph ere to a stirred suspen sion
of ch rom ium (VI) oxide (62 m g, 0.62 m m ol) an d an h ydrous m agn esium sulfate (50 m g,
0.42 m m ol) in dich lorom eth an e (1.75 m l). After stirrin g at 0 °C for 30 m in , a solution of al-
coh ol 25 (45 m g, 0.15 m m ol) in dich lorom eth an e (0.9 m l) was added. Th e m ixture was
stirred at 0 °C for 30 m in an d th en at room tem perature for 2 h . Th e m ixture was diluted
with ligh t petroleum (10 m l) an d filtered th rough a colum n of alum in a (10 g) wh ich was
th en wash ed with th e sam e solven t (20 m l). Th e com bin ed filtrates were con cen trated in
vacuum . Pyridin e was rem oved from th e residue by coevaporation with toluen e. Yield of al-
deh yde 26: 26 m g (58%), m .p. 136–137 °C (aceton e–h eptan e, un der argon ), [α]D +59 (c 1.1).
IR: 2 820, 2 725 (C–H in CHO); 1 713 (C=O); 990 (C–F). 1H NMR: 0.75 s, 3 H (3 × H-18);
0.79 s, 3 H (3 × H-19); 4.81 dm , 1 H, J(F,H-3) = 49 (H-3); 9.77 d, 1 H, J = 2.2 (CH=O). For
C
20H31FO (306.5) calculated: 78.38% C, 10.20% H; foun d: 78.27% C,10.11% H.
3α-Hydroxy-5α-an drostan e-17β-carboxylic Acid (28)
Potassium h ydroxide (1.0 g, 17.82 m m ol) in water (2.5 m l) was added to a solution of
m eth yl 3α-h ydroxy-5α-an drostan e-17β-carboxylate15 27 (1.0 g, 2.99 m m ol) in eth ylen e gly-
col (15 m l) an d th e reaction m ixture was h eated at reflux for 20 m in . Th e m ixture was
poured in to brin e with h ydroch loric acid an d th e product was extracted with eth yl acetate,
wash ed with water, an d dried over an h ydrous sodium sulfate. Evaporation of th e solven t af-
forded carboxylic acid 28 (0.88 g, 92%), m .p. 282–284 °C (ref.16 gives 282–285 °C). IR: 3 615
(OH); 3 512, 2 666 (COOH); 1 737, 1 700 (C=O); 1 002 (C–OH). 1H NMR: 0.72 s, 3 H (3 ×
H-18); 0.79 s, 3 H (3 × H-19); 2.39 t, 1 H, J = 9.4 (H-17); 4.05 m , 1 H, W1/2 = 6.8 (H-3).
Trieth ylam m on ium 3α-Hydroxy-5α-an drostan e-17β-carboxylate (29)
A solution of carboxylic acid 28 (120 m g, 0.37 m m ol) was h eated at reflux with trieth yl-
am in e (10 m l) for 2 h . Th e solven t was rem oved in a vacuum an d th e residue was crystal-
lized from aceton e–h eptan e, yield 56 m g (35%), m .p. 266–268 °C. IR: 3 289 (OH); 1 740,
1 408 (COO–); 1 004 (C–OH). 1H NMR: 0.71 s, 3 H (3 × H-18); 0.78 s, 3 H (3 × H-19); 1.20 t,
9 H, J = 7.3 (3 × CH3-CH2); 2.37 t, 1 H, J = 9.4 (H-17); 2.92 q, 6 H, J = 7.3 (3 × CH2-N); 4.04
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

3α-Fluoro Analogues of Allopregnanolone
43
m , 1 H, W1/2 = 6.8 (H-3). For C26H47NO3 (421.7) calculated: 74.06% C, 11.24% H, 3.32% N;
foun d: 73.89% C, 11.08% H, 3.19% N.
3α-Acetoxy-21-n or-5α-pregn an -20-ol (30)
Acetic an h ydride (0.90 g, 8.82 m m ol) was added to a solution of carboxylic acid 28 (100 m g,
0.31 m m ol) in pyridin e (1.5 m l) an d th e m ixture was allowed to stan d at room tem perature
for 18 h . Th e m ixture was th en poured in ice-cool water with h ydroch loric acid. Th e prod-
uct was extracted with eth yl acetate, wash ed with water an d dried over sodium sulfate. After
evaporation to dryn ess, th e residue (90 m g) an d trieth ylam in e (0.04 m l) were dissolved in
tetrah ydrofuran (1.4 m l) an d cooled to 0 °C. Eth yl ch loroform ate (0.02 m l, 0.2 m m ol) was
added, followed with a solution of sodium boroh ydride (47 m g, 1.24 m m ol) in water
(1.75 m l) after 20 m in . After stan din g at room tem perature for 2 h , th e m ixture was poured
in to water acidified by h ydroch loric acid. Th e product was extracted with eth er, wash ed suc-
cessively with dilute h ydroch loric acid, water, th e saturated solution of potassium
h ydrogen carbon ate, water an d dried over an h ydrous sodium sulfate. Evaporation of th e sol-
ven t afforded alcoh ol 30 (60 m g, 54%), m .p. 100–102 °C (aceton e). IR: 3 623, 3 509 (OH);
1 726, 1 714 (C=O); 1 266, 1 251, 1 241, 1 020 (C–O); 1 061 (C–OH). 1H NMR: 0.64 s, 3 H
(3 × H-18); 0.80 s, 3 H (3 × H-19); 2.05 s, 3 H (CH3COO); 3.56 dd, 1 H, J = 7 an d J′ = 10
(H-20A); 3.72 dd, 1 H, J = 7 an d J′ = 10 (H-20B); 5.01 m , 1 H, W1/2 = 7 (H-3). For C22H36O3
(348.5) calculated: 75.82% C, 10.41% H; foun d: 75.70% C, 10.36% H.
3α-Acetoxy-21-n or-5α-pregn an -20-al (31)
Pyridin e (0.2 m l) was added dropwise at 0 °C in argon atm osph ere to a stirred suspen sion
of ch rom ium (VI) oxide (124 m g, 1.24 m m ol) an d an h ydrous m agn esium sulfate (100 m g,
0.84 m m ol) in dich lorom eth an e (3.5 m l). After stirrin g at 0 °C for 30 m in , a solution of al-
coh ol 30 (100 m g, 0.29 m m ol) in dich lorom eth an e (2.0 m l) was added. Th e m ixture was
stirred at 0 °C for 30 m in an d th en at room tem perature for 2 h . Th e m ixture was diluted
with h exan e (20 m l) an d filtered th rough a colum n of alum in a (20 g) wh ich was th en
wash ed with th e sam e solven t (30 m l). Th e com bin ed filtrates were con cen trated in a vac-
uum . Pyridin e was rem oved from th e residue by coevaporation with toluen e. Yield of alde-
h yde 70 m g (70%), m .p. 118–120 °C (aceton e–h eptan e). IR: 2 820, 2 724 (CH=O); 1 724,
1 714 (C=O); 1 266, 1 251, 1 241 (C–O). 1H NMR: 0.75 s, 3 H (3 × H-18); 0.80 s, 3 H (3 ×
H-19); 2.05 s, 3 H (CH3COO); 5.01 m , 1 H, W1/2 = 7 (H-3); 9.77 d, 1 H, J = 2.0 (CH=O). For
C
22H34O3 (346.5) calculated: 76.26% C, 9.89% H; foun d: 76.29% C, 9.81% H.
3α-Hydroxy-21-n or-5α-pregn an -20-al (32)
Potassium carbon ate (33.5 m g, 0.24 m m ol) was added to a solution of aldeh yde 31 (70 m g,
0.20 m m ol) in m eth an ol (3.4 m l). Th e reaction m ixture was allowed to stan d at room tem -
perature for 18 h . Th e m ixture was th en n eutralized with brin e con tain in g h ydroch loric acid
an d th e product was extracted with ch loroform . Th e organ ic ph ase was wash ed with water
an d dried over an h ydrous sodium sulfate. Evaporation of th e solven t an d ch rom atograph y
of th e residue on two preparative plates afforded th e startin g com poun d 31 (33 m g) an d al-
coh ol 32 (31 m g, 50%), m .p. 136–138 °C (aceton e–h eptan e) (ref.17 gives 137–138 °C). IR:
3 615 (OH), 2 725 (C–H in CHO), 1 715 (C=O). 1H NMR: 0.74 s, 3 H (3 × H-18); 0.79 s, 3 H
(3 × H-19); 4.05 m , 1 H, W1/2 = 7 (H-3); 9.77 d, 1 H, J = 1.8 (CH=O).
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

44
Slavíková et al.:
3,3-Difluoro-5α-pregn an -20-on e (33)
A) A solution of (20R)-3,3-difluoro-5α-pregn an -20-ol (40; 50 m g, 0.15 m m ol) in aceton e
(1 m l) was oxidized with Jon es reagen t (1 m l) un til purple colour of th e m ixture persisted
for 2 m in . After stan din g at room tem perature for 5 m in , th e excess reagen t was reduced
with 2-propan ol (2 m l) an d th e m ixture was poured in to water. Th e product was extracted
with eth er, wash ed with water, th e potassium h ydrogen carbon ate solution , water an d dried.
Evaporation of th e solven t gave com poun d 33 th at crystallized from aceton e–h eptan e, yield
25 m g (50%), m .p. 138–140 °C (ref.19 gives 145–147 °C), [α]D +87 (c 1.2). IR: 1 698, 1 362
(COCH3); 1 092 (C–F). 1H NMR: 0.61 s, 3 H (3 × H-18); 0.83 s, 3 H (3 × H-19); 2.11 s, 3 H
(3 × H-21); 2.52 t, 1 H, J = 9 (H-17).
B) An alogously, (20S)-3,3-difluoro-5α-pregn an -20-ol (41; 50 m g, 0.15 m m ol) yielded
keton e 33 (32 m g, 64%), iden tical with th e sam ple prepared above.
(20R)-3-Oxo-5α-pregn an -20-yl Ben zoate (36)
Th e ben zoate 36 was prepared from (20R)-20-h ydroxy-5α-pregn an -3-on e20 (34) in th e sam e
way as com poun d 37, m .p. 183–185 °C (eth an ol) (ref.21 gives 184-185 °C). 1H NMR: 0.68 s,
3 H (3 × H-18); 0.96 s, 3 H (3 × H-19); 1.26 d, 3 H, J = 6 (3 × H-21); 5.13 m , 1 H, W1/2 = 21
(H-20); 7.48 m , 3 H an d 8.05 m , 2 H (ben zoate).
(20S)-3-Oxo-5α-pregn an -20-yl Ben zoate (37)
Ben zoyl ch loride (0.5 m l, 4.3 m m ol) was added to
a solution of (20S)-20-h ydroxy-
5α-pregn an -3-on e20 (35; 400 m g, 1.26 m m ol) in pyridin e (0.5 m l) an d th e reaction m ixture
was left stan din g at room tem perature. After 20 h , th e m ixture was poured in to h ot water
an d th e product was extracted with ch loroform . Th e extract was successively wash ed with
water, dilute h ydroch loric acid, water, th e potassium h ydrogen carbon ate solution an d dried.
After evaporation of th e solven t, th e residue crystallized from eth an ol yieldin g ben zoate 37
(420 m g, 79%), m .p. 185–187 °C. IR: 1 706, 1 284 (COO); 1 378 (CH3); 3 026, 1 603, 1 451
(arom .). 1H NMR: 0.74 s, 3 H (3 × H-18); 1.01 s, 3 H (3 × H-19); 1.35 d, 3 H, J = 6 (3 × H-21);
5.16 m , 1 H, W1/2 = 21 (H-20); 7.48 m , 3 H an d 8.05 m , 2 H (ben zoate). For C28H38O3
(422.6) calculated: 79.58% C, 9.06% H; foun d: 79.50% C, 8.94% H.
(20R)-3,3-Difluoro-5α-pregn an -20-yl Ben zoate (38)
(20R)-Ben zoate 36 (118 m g, 0.28 m m ol) was treated with DAST (1.22 g, 7.57 m m ol) in th e
sam e way as in th e preparation of com poun d 39. Yield of com poun d 38 was 55 m g (44%),
m .p. 153–154 °C (m eth an ol), [α]D –21 (c 1.3). IR: 1 705, 1 282, 960 (COO); 1 376 (CH3);
3 031, 1 603, 1 452, 1 002 (arom .); 1 093 (C–F). 1H NMR: 0.66 s, 3 H (3 × H-18); 0.78 s, 3 H
(3 × H-19); 1.26 d, 3 H, J = 6 (3 × H-21); 5.13 m , 1 H, W1/2 = 18 (H-20); 7.48 m , 3 H an d
8.05 m , 2 H (ben zoate). For C28H38F2O2 (444.6) calculated: 75.64% C, 8.61% H; foun d:
75.50% C, 8.49% H.
(20S)-3,3-Difluoro-5α-pregn an -20-yl Ben zoate (39)
Ben zoate 37 (100 m g, 0.24 m m ol) in
a glass tube was dissolved in DAST (1.22 g,
7.57 m m ol). Th e tube was sealed an d h eated to 80 °C. After 8 h , th e tube was cooled to 0 °C
an d open ed. Th e m ixture was diluted with dich lorom eth an e (8 m l), an d th e solution was
Collect. Czech. Chem. Commun. (Vol. 67) (2002)

3α-Fluoro Analogues of Allopregnanolone
45
wash ed with th e potassium h ydrogen carbon ate solution (30 m l) an d with water. Th e solven t
was evaporated in a vacuum an d th e residue was ch rom atograph ed on a colum n of silica gel
(10 m l). Elution with a m ixture of ligh t petroleum –eth er (98 : 2) an d crystallization yielded
com poun d 39 (50 m g, 47%), m .p. 189–191 °C (m eth an ol), [α]D +35 (c 1.3). IR: 1 707, 1 284,
964 (COO); 1 375 (CH3); 3 031, 1 603, 1 451 (arom .); 1 093 (C–F). 1H NMR: 0.72 s, 3 H (3 ×
H-18); 0.83 s, 3 H (3 × H-19); 1.35 d, 3 H, J = 6 (3 × H-21); 5.18 m , 1 H, W1/2 = 16 (H-20);
7.48 m , 3 H an d 8.05 m , 2 H (ben zoate). For C28H38F2O2 (444.6) calculated: 75.64% C,
8.61% H; foun d: 75.48% C, 8.53% H.
(20R)-3,3-Difluoro-5α-pregn an -20-ol (40)
Ben zoate 38 (157 m g, 0.35 m m ol) was h ydrolyzed in a solution of potassium h ydroxide in
eth an ol (5%, 15 m l) at reflux tem perature. After 3 h , th e m ixture was con cen trated in a vac-
uum to a h alf of its origin al volum e an d poured in to brin e. Th e precipitate was extracted
with ch loroform , an d th e organ ic ph ase was wash ed with th e solution of h ydroch loric acid,
water, th e potassium h ydrogen carbon ate solution an d water. Th e solution was dried an d th e
solven t rem oved. Crystallization afforded com poun d 40 (57 m g, 47%), m .p. 173–174 °C (ac-
eton e–h eptan e), [α]D +3 (c 1.5). IR: 3 610, 3 464, 1 102 (OH); 1 374 (CH3); 1 092 (C–F).
1H NMR: 0.75 s, 3 H (3 × H-18); 0.83 s, 3 H (3 × H-19); 1.13 d, 3 H, J = 6 (3 × H-21); 3.72 m ,
1 H, W 1/2 = 18 (H-20). For C21H34F2O (340.5) calculated: 74.08% C, 10.06% H; foun d:
73.91% C, 9.89% H.
(20S)-3,3-Difluoro-5α-pregn an -20-ol (41)
Ben zoate 39 (50 m g, 0.11 m m ol) was h ydrolyzed in th e sam e way as above to yield com -
poun d 41 (22 m g, 57%), m .p. 158–159 °C (aceton e–h eptan e), [α]D +12 (c 1.4). IR: 3 615,
3 464, 1 072 (OH); 1 374 (CH3); 1 093 (C–F). 1H NMR: 0.66 s, 3 H (3 × H-18); 0.83 s, 3 H
(3 × H-19); 1.24 d, 3 H, J = 6 (3 × H-21); 3.70 m , 1 H, W1/2 = 16 (H-20). For C21H34F2O
(340.5) calculated: 74.08% C, 10.06% H; foun d: 73.92% C, 9.84% H.
3α-Fluoro-5β-pregn an -20-on e (43)
Followin g th e gen eral procedure, 3β-h ydroxy-5β-pregn an -20-on e22 (44; 376 m g, 1.18 m m ol)
was treated with DAST (366 m g, 2.27 m m ol) in dich lorom eth an e (8 m l) at room tem pera-
ture for 2 h . Ch rom atograph y was carried out on a colum n of silica gel (20 g). Elution with
a m ixture of ligh t petroleum –eth er (96 : 4) yielded 102 m g of com poun d 43 (27%), m .p.
107–108 °C (aceton e–h eptan e), [α]D +106 (c 1.2). IR: 1 698 (C=O), 1 002 (C–F). 1H NMR:
0.60 s, 3 H (3 × H-18); 0.93 s, 3 H (3 × H-19); 2.12 s, 3 H (3 × H-21); 4.52 dm , 1 H, J(F,H-3) =
49 (H-3). For C21H33FO (320.5) calculated: 78.70%C, 10.38% H; foun d: 78.63% C, 10.29% H.
This work was supported by grants Nos 4668-3, S 5011007, 203/01/0084 and Z4 055 905.
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