Diastereospecific conjugation of 24-oxo-25,26,27-trinor analogs of ecdysteroids with L-ascorbic acid

Article abstract of DOI:10.1134/S1070428013120166

Acid-catalyzed acetalization of 24-oxo-25,26,27-trinor analogs of ecdysteroids in the reaction with 2,3-di-O-benzylascorbic acid diastereospecifically gives the corresponding S-diastereoisomer with respect to the acetal chiral center.

Full text of DOI:10.1134/S1070428013120166

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2013, Vol. 49, No. 12, pp. 1807–1811. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © R.G. Savchenko, S.A. Kostyleva, V.N. Odinokov, 2013, published in Zhurnal Organicheskoi Khimii, 2013, Vol. 49, No. 12,
pp. 1825–1829.
Diastereospecific Conjugation of 24-Oxo-25,26,27-trinor Analogs
of Ecdysteroids with L-Ascorbic Acid
R. G. Savchenko, S. A. Kostyleva, and V. N. Odinokov
Institute of Petrochemistry and Catalysis, Russian Academy of Sciences,
pr. Oktyabrya 141, Ufa, 450075 Bashkortostan, Russia
e-mail: odinokov@anrb.ru
Received June 21, 2013
Abstract—Acid-catalyzed acetalization of 24-oxo-25,26,27-trinor analogs of ecdysteroids in the reaction with
2,3-di-O-benzylascorbic acid diastereospecifically gives the corresponding S-diastereoisomer with respect to
the acetal chiral center.
DOI: 10.1134/S1070428013120166
Ecdysteroids are hormones responsible for moult-
ing, metamorphosis, and diapause of insects and crus-
taceans. Ecdysteroids are also produced (and in higher
amounts) by some plants, which makes it possible to
isolate these structurally unique polyhydroxy sterols
and explore their properties and chemical transforma-
tions [1–5]. Ecdysteroids are not toxic to warm-
blooded animals and humans; moreover, they have
diverse positive effects on the human organism [6].
An up-to-date approach to the design of new medical
agents is based on conjugation of compounds whose
biological activity is known. This may lead to syner-
gistic effect or appearance of new biologically impor-
tant properties. For example, a conjugate of ecdy-
steroid and α-tocopherol analog was shown [7] to be
a potent antioxidant which inhibited lipid peroxidation
more efficiently than did the initial 20-hydroxyecdy-
sone and α-tocopherol; it also enhanced the activity of
catalase and superoxide dismutase [8, 9]. In recent
years, attention was given to conjugates of L-ascorbic
acid (2,3-dehydro-L-gulonic acid γ-lactone, vita-
min C); in particular, a conjugate of L-ascorbic acid
with α-tocopherol turned out to be highly efficient in
the protection of liver and myocardium cell mem-
branes from free radical damage, and its efficiency
exceeded that of α-tocopherol and ascorbic acid taken
alone [10].
(IV) and 2,3-di-O-acetyl-20,22-acetonide VI as mix-
tures with oxo derivatives III and V (obtained by
ozonolysis of selectively protected ω-anhydro-20-
hydroxyecdysones I and II [11, 12]) were brought into
acid-catalyzed condensation with (4R,5S)-2,3-O-diben-
zylascorbic acid (VII) prepared from commercially
available L-(+)-ascorbic acid [13] (Scheme 1).
The reaction of equimolar amounts of diacetonide
IV and compound VII in benzene in the presence of
p-toluenesulfonic acid (TsOH) gave conjugate VIII
(yield 15%) and its 2,3-deprotected 14,15-dehydrated
derivative, compound IX (yield 23%). Relatively easy
removal of 2,3-acetonide protection from ecdysteroid
2,3:20,22-diacetonides under acidic conditions and
dehydration involving the 14α-hydroxy group were
reported previously [7, 14, 15]. We succeeded in
minimizing side processes by using 2,3-diacetyl pro-
tection instead of 2,3-acetonide. The condensation of
aldehyde VI with compound VII under analogous
conditions was more selective, and conjugate X was
isolated in 48% yield.
1
The H and 13C NMR spectra of VIII and X con-
tained signals typical of structural fragments of the
initial ecdysteroids IV and VI and ascorbic acid deriv-
ative VII. Signals were assigned using homo- and
heteronuclear correlation techniques (COSY, NOESY,
HSQC, HMBC), as well as by comparing with the
spectra of the initial compounds.
Compound IX displayed in the 13C NMR spectrum
only one signal (δC 106.63) assignable to quaternary
acetal carbon atom, which confirmed deprotection of
Ascorbic acid conjugates with ecdysteroids have
not been reported previously. We were the first to syn-
thesize such compounds. For this purpose, 24-oxo-
25,26,27-trinorponasterone A 2,3:20,22-diacetonide
1807

SAVCHENKO et al.
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DIASTEREOSPECIFIC CONJUGATION OF 24-OXO-25,26,27-TRINOR ANALOGS
1809
the 2,3-dihydroxy fragment (the 13C NMR spectrum of
20-hydroxyecdysone diacetonide contains two signals
at δC 106.68 and 108.20 ppm [16]). In the sp2-carbon
region we observed additional signals from disubsti-
tuted (δC 147.12 ppm) and monosubstituted
(δC 120.30 ppm) double-bonded carbon atoms result-
ing from elimination of the 14α-hydroxy group. Analo-
gous double bond is present in the molecules of
stachysterone B derivatives [16].
internal reference. Standard homo- and heteronuclear
COSY, HSQC, and HMBC techniques (Bruker) were
applied. The mass spectra were obtained on a Bruker-
Autoflex III spectrometer (MALDI TOF, positive ion
detection) using 2,5-dihydroxybenzoic acid and
α-cyano-4-hydroxycinnamic acid as matrices. The
melting points were measured on a Boetius micro hot
stage. The elemental compositions were determined on
a Carlo Erba EA-1108 CHNS-O analyzer. Silica gel
KSKG 100/200 was used for column chromatography.
Analytical thin-layer chromatography was performed
on Silufol plates; spots were visualized by treatment
with a solution of vanillin in ethanol acidified with
sulfuric acid.
The formation of conjugates is confirmed by the
presence in the spectra of VIII–X of signals from
tertiary acetal carbon atoms (C24) in the region
δC 101.4–103.5 ppm, which showed cross peaks with
hydrogen atoms resonating at δ 5.12–5.14 ppm in the
HSQC spectra (cf. [7, 10]). The structure of the ob-
tained compounds was also confirmed by the MALDI
TOF mass spectra.
(20R,22R)-14α-Hydroxy-2β,3β:20,22-bis(iso-
propylidenedioxy)-27-nor-5β-cholest-7-ene-6,25-
dione (III) and (20R,22R)-14α-hydroxy-2β,3β:20,22-
bis(isopropylidenedioxy)-6-oxo-25,26,27-trinor-
5β-cholest-7-ene-24-al (IV). A solution of 0.3 g
(0.55 mmol) of compound I in 6 mL of methylene
chloride–pyridine (5:1) was cooled to 0°C, and
an ozone/oxygen mixture was passed through the
solution at a flow rate of 10 mL/min under vigorous
stirring over a period of 3 min (until 0.55 mmol of O3
was absorbed). The mixture was purged with argon
and evaporated, and the residue was subjected to
chromatography on 9 g of silica gel using chloroform–
methanol (20:1) as eluent. We isolated 0.09 g (30%) of
compound III, Rf 0.6 (CHCl3–MeOH, 10:1), and
0.17 g (60%) of IV, Rf 0.5 (CHCl3–MeOH, 10:1). The
1H and 13C NMR spectra of the products were identical
to those given in [11].
The presence of only one C24 signal in the 13C
NMR spectra of VIII–X indicates configurational
homogeneity of the newly formed acetal chiral center
and hence stereospecificity of the conjugation of
ω-formyl analogs of ecdysteroids with 2,3-O-dibenzyl-
ascorbic acid (VII). However, the condensation of
racemic (6-benzyloxy-2,5,7,8-tetramethylchroman-2-
yl)acetaldehyde at the vicinal hydroxy groups of ecdy-
steroids gave mixtures of diastereoisomers [7].
Presumably, stereospecific formation of acetals VIII–
X is determined by spatial proximity of the aldehyde
group to the homochiral C20 and C22 atoms in ecdy-
steroidal aldehydes IV and VI. The NOESY spectrum
of X revealed coupling of the acetal proton (C24H)
with proton on C5′ in the ascorbic acid fragment, which
suggests cis orientation of these protons in the
dioxolane ring and therefore S configuration of the
new chiral center (C24). The presence in the NOESY
spectrum of a cross peak between 24-H and proton on
C22 in the ecdysteroid fragment corresponds to more
favorable conformation of molecule X with anti
orientation of the dioxolane rings linked by methylene
group.
(20R,22R)-2β,3β-Diacetoxy-14α-hydroxy-20,22-
isopropylidenedioxy-27-nor-5β-cholest-7-ene-6,25-
dione (V) and (20R,22R)-2β,3β-diacetoxy-14α-hy-
droxy-20,22-isopropylidenedioxy-6-oxo-25,26,27-
trinor-5β-cholest-7-en-24-al (VI). An ozone/oxygen
mixture was passed at a flow rate of 10 mL/min over
a period of 3 min through a solution of 0.25 g
(0.43 mmol) of compound II in 5 mL of methylene
chloride–pyridine (5:1) under vigorous stirring at 0°C
(until 0.43 mmol of O3 was absorbed). The mixture
was then treated as described above. We isolated
0.09 g (36%) of compound V, Rf 0.68 (CHCl3–MeOH,
Reductive debenzylation of X quantitatively
afforded (5R)-3,4-dihydroxy-5-{(2S,4S)-2-[(20R,22R)-
2β,3β-diacetoxy-14α-hydroxy-20,22-isopropylidene-
dioxy-6-oxo-24,25,26,27-tetranor-5β-cholest-7-en-23-
yl]-1,3-dioxolan-4-yl}furan-2(5H)-one (XI).
1
10:1), which was identical (in H and 13C NMR spec-
tra) to a sample described in [12], and 0.12 g (50%)
of compound VI, Rf 0.42 (CHCl3–MeOH, 10:1),
mp 165–166°C, [α]D20 = +53.0° (c = 0.62, CHCl3).
1H NMR spectrum (CDCl3), δ, ppm: 0.78 s (3H,
C18H3), 1.00 s (3H, C19H3), 1.15 s (3H, C21H3), 1.34 s
and 1.40 s (3H each, 20,22-Me2C), 1.48–2.68 m (16H,
EXPERIMENTAL
The H and 13C NMR spectra were recorded on
a Bruker Avance-400 spectrometer at 400.13 and
100.62 MHz, respectively, using tetramethylsilane as
1
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 12 2013

SAVCHENKO et al.
1810
CH, CH2), 1.98 s and 2.09 s (3H each, MeCO),
2.35 d.d (1H, 5-H, J = 11.6, 5.6 Hz), 3.10 m (1H, 9-H,
w1/2 = 25.6 Hz), 4.19 m (1H, 22-H, w1/2 = 10.8 Hz),
5.04 m (1H, 2-H, w1/2 = 15.6 Hz), 5.30 br.s (1H, 3-H,
w1/2 = 9.6 Hz), 5.84 s (1H, 7-H), 9.79 br.s (1H, CHO,
w1/2 = 7.6 Hz). 13C NMR spectrum (CDCl3), δC, ppm:
16.97 (C18), 20.37 (C11), 21.06 (MeCO), 21.12 (C16),
22.12 (C21), 23.80 (C19), 26.88 (C15), 28.80 and 29.09
(Me2C), 30.81 (C12), 31.46 (C4), 33.60 (C9), 33.93
(C1), 38.30 (C10), 43.20 (C23), 47.15 (C13), 50.91 (C5),
48.88 (C17), 67.03 (C3), 68.67 (C2), 75.43 (C22), 84.05
(C20), 84.43 (C14), 121.47 (C7), 107.97 (Me2C), 164.83
(C8), 170.28 and 170.59 (MeCO), 200.34 (C24), 202.32
(C6). Mass spectrum: m/z 583.309 [M + Na]+. Found,
%: C 66.41; H 7.89. C31H44O9. Calculated, %: C 66.98;
H 8.04.
C 70.24; H 7.31. C50H62O12. Calculated, %: C 69.98;
H 7.84. M + K 893.387.
Compound IX. mp 134–136°C, [α]D20 = –1.5° (c =
1
0.40, CHCl3). H NMR spectrum (CDCl3), δ, ppm:
1.00 s (3H, C18H3), 1.22 s (3H, C19H3), 1.25 s (3H,
C21H3), 1.34 s and 1.45 s (3H each, 20,22-Me2C),
1.61–2.32 m (15H, CH, CH2), 2.53 m (1H, 5-H, w1/2
=
22.4 Hz), 3.18 m (1H, 9-H, w1/2 = 9.2 Hz), 3.94 m (2H,
6′-H, 22-H), 4.04 m (2H, 3-H, 6′-H), 4.19 m (1H, 2-H,
w1/2 = 16.8 Hz), 4.57 m (1H, 5′-H, w1/2 = 12.0 Hz),
4.72 d (1H, 4′-H, J = 2.4 Hz), 5.10 m (1H, 24-H, w1/2
=
12.0 Hz), 5.12 s (2H, 2′-OCH2), 5.20 s (2H, 3′-OCH2),
5.26 m (1H, 15-H, w1/2 = 5.6 Hz), 5.42 s (1H, 7-H),
7.23–7.39 m (10H, Harom). 13C NMR spectrum (CDCl3),
δC, ppm: 16.73 (C18), 20.50 (C11), 21.77 (C21), 26.15
and 28.30 (Me2C), 27.44 (C12), 28.10 (C19), 34.24 (C4),
35.78 (C16), 37.67 (C23), 37.90 (C1, C9), 42.23 (C10),
45.13 (C13), 52.33 (C5), 55.10 (C17), 68.14 (C2, C3),
69.11 (C6′), 72.84 (3′-OCH2), 73.06 (2′-OCH2), 74.13
(C5′), 75.18 (C4′), 76.55 (C22), 82.50 (C20), 101.44
(C24), 106.68 (Me2C), 118.39 (C7), 120.30 (C15);
127.05, 127.89, 128.33 (C6H5); 134.49 (C3′), 135.12
(C2′), 147.12 (C14), 156.37 (C8), 172.00 (C1′), 202.92
(C6). Found, %: C 70.83; H 7.08. C47H56O11. Calculat-
ed, %: C 70.21; H 7.79.
(5R)-3,4-Dibenzyloxy-5-{(2S,4S)-2-[(20R,22R)-
14α-hydroxy-2,3:20,22-bis(isopropylidenedioxy)-6-
oxo-24,25,26,27-tetranor-5β-cholest-7-en-23-yl]-1,3-
dioxolan-4-yl}furan-2(5H)-one (VIII) and (5R)-3,4-
dibenzyloxy-5-{(2S,4S)-2-[(20R,22R)-2β,3β-dihy-
droxy-20,22-isopropylidenedioxy-6-oxo-24,25,26,27-
tetranor-5β-cholesta-7,14-dien-23-yl]-1,3-dioxolan-
4-yl}furan-2(5H)-one (IX). Aldehyde IV, 0.20 g
(0.39 mmol), was dissolved in 3 mL of anhydrous
benzene, 0.02 g of p-toluenesulfonic acid was added,
the mixture was stirred for 20 min at room tempera-
ture, a solution of 0.14 g (0.39 mmol) of compound
VII in 3 mL of anhydrous benzene was added, and the
mixture was stirred for 24 h at room temperature (until
the initial compounds disappeared according to the
TLC data). The mixture was treated with 5 mL of
water and 0.02 mL of a saturated solution of NaHCO3
and extracted with ethyl acetate (3×15 mL), the extract
was evaporated, and the residue was subjected to
chromatography on 8.5 g of silica gel using chloroform
as eluent. We isolated 0.05 g (15%) of compound VIII,
Rf 0.5 (CHCl3–MeOH, 10:1), and 0.07 g (23%) of IX,
Rf 0.4 (CHCl3–MeOH, 10:1).
(5R)-3,4-Dibenzyloxy-5-{(2S,4S)-2-[(20R,22R)-
2β,3β-diacetoxy-14α-hydroxy-20,22-isopropylidene-
dioxy-6-oxo-24,25,26,27-tetranor-5β-cholest-7-en-
23-yl]-1,3-di-oxolan-4-yl}furan-2(5H)-one (X).
Aldehyde VI, 0.17 g (0.3 mmol), was dissolved in
3 mL of anhydrous benzene, 0.02 g of p-toluenesulfonic
acid was added, the mixture was stirred for 20 min at
room temperature, 0.11 g (0.3 mmol) of compound VII
in 3 mL of anhydrous benzene was added, and the mix-
ture was stirred for 24 h at room temperature (until the
initial compounds disappeared according to the TLC
data). The mixture was then treated as described above
for the reaction with aldehyde IV. Yield 0.13 g (48%),
Rf 0.5 (CHCl3–MeOH, 10:1), mp 119–121°C, [α]D20
=
Compound VIII. mp 99–101°C, [α]D20 = 7.8° (c =
+60.3° (c = 0.71, CHCl3). 1H NMR spectrum (CDCl3),
δ, ppm: 0.80 s (3H, C18H3), 1.04 s (3H, C19H3), 1.14 s
(3H, C21H3), 1.34 s and 1.41 s (3H each, 20,22-Me2C),
1.63 m and 1.80 m (2H, 11-H), 1.67 m and 1.92 m
(2H, 1-H), 1.83–2.05 (11H, CH, CH2), 2.12 s and
1
0.33, CHCl3). H NMR spectrum (CDCl3), δ, ppm:
1.00 s (3H, C18H3), 1.23 s (3H, C19H3), 1.28 s (3H,
C21H3), 1.35 s and 1.45 s (3H each, 20,22-Me2C),
1.37 s and 1.43 s (3H each, 2,3-Me2C), 1.52–2.67 m
(18H, CH, CH2), 4.00 m (1H, 22-H), 4.12 m (2H,
6′-H), 4.25 m (1H, 5′-H, w1/2 = 27.6 Hz), 4.55 d (1H,
4′-H, J = 2.4 Hz), 4.72 m (1H, 3-H, w1/2 = 14.8 Hz),
4.75 br.s (1H, 2-H, w1/2 = 5.2 Hz), 5.12 m (1H, 24-H,
w1/2 = 11.6 Hz), 5.14 s (2H, 2′-OCH2), 5.20 s (2H,
3′-OCH2), 5.85 s (1H, 7-H), 7.22–7.40 m (10H, Harom).
Mass spectrum: m/z 893.674 [M + K]+. Found, %:
2.18 s (3H each, MeCO), 2.23 m (1H, 17-H, w1/2
=
7.6 Hz), 2.41 d.d (1H, 5-H, J = 12.8, 4.0 Hz), 3.12 m
(1H, 9-H, w1/2 = 23.2 Hz), 3.92 m (1H, 22-H), 3.94 m
and 4.08 m (2H, 6′-H), 4.23 m (1H, 5′-H), 4.60 d (1H,
4′-H, J = 3.6 Hz), 5.14 m (1H, 24-H, w1/2 = 7.6 Hz),
5.16 m (1H, 2-H, w1/2 = 6.8 Hz), 5.18 s (2H, 2′-OCH2),
5.20 s (2H, 3′-OCH2), 5.38 br.s (1H, 3-H, w1/2
=
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 49 No. 12 2013

DIASTEREOSPECIFIC CONJUGATION OF 24-OXO-25,26,27-TRINOR ANALOGS
1811
11.2 Hz), 5.84 s (1H, 7-H), 7.22–7.39 m (10H, Harom).
13C NMR spectrum (CDCl3), δC, ppm: 17.06 (C18),
20.37 (C11), 20.90 and 21.11 (MeCO), 21.90 (C21, C16),
23.85 (C19), 26.92 and 28.92 (Me2C), 29.68 (C15),
30.80 (C4), 31.56 (C12), 33.57 (C23), 33.64 (C9), 34.02
(C1), 38.38 (C10), 47.20 (C13), 48.72 (C17), 51.01 (C5),
65.96 (C6′), 67.06 (C3), 68.68 (C2), 73.64 (2′-OCH2),
73.88 (3′-OCH2), 74.16 (C5′), 74.97 (C4′), 76.85 (C22),
84.21 (C20), 84.67 (C14), 103.48 (C24), 107.44 (Me2C),
121.47 (C7, C2′); 127.77, 128.66, 128.71, 129.11
(C6H5); 156.40 (C3′), 164.79 (C8), 168.98 (C1′), 170.19
and 170.39 (MeCO), 202.26 (C6). Mass spectrum, m/z:
921.401 [M + Na]+, 937.394 [M + K]+. Found, %:
C 68.13; H 6.95. C51H62O14. Calculated, %: C 68.48;
H 7.09. M + Na 921.403, M + K 937.377.
spectrum: m/z 723.463 [M – H2O + Na]+. Found, %:
C 61.83; H 7.01. C37H50O14. Calculated, %: C 61.28;
H 7.69. M – H2O + Na 723.309.
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(5R)-3,4-Dihydroxy-5-{(2S,4S)-2-[(20R,22R)-
2β,3β-diacetoxy-14α-hydroxy-20,22-isopropylidene-
dioxy-6-oxo-24,25,26,27-tetranor-5β-cholest-7-en-
23-yl]-1,3-di-oxolan-4-yl}furan-2(5H)-one (XI).
Hydrogen was passed over a period of ~3 h through
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and 0.04 g of 10% Pd/C in 5 mL of anhydrous ethanol,
the progress of the reaction being monitored by TLC.
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[α]D20 = +21.0° (c = 0.41, MeOH). H NMR spectrum
1
(CD3OD), δ, ppm: 0.85 s (3H, C18H3), 1.04 s (3H,
C19H3), 1.20 s (3H, C21H3), 1.34 s and 1.42 s (3H each,
20,22-Me2C), 1.56–1.85 (17H, CH, CH2), 2.00 s and
2.13 s (3H each, MeCO), 2.33 m (1H, 17-H, w1/2
=
10.4 Hz), 2.36 m (1H, 5-H, w1/2 = 7.2 Hz), 3.37 m
(1H, 9-H, w1/2 = 14.8 Hz), 3.95 m (1H, 22-H), 3.97 m
and 4.07 m (2H, 6′-H), 4.35 m (1H, 5′-H), 4.80 m (1H,
4′-H), 5.04 m (1H, 24-H, w1/2 = 11.6 Hz), 5.11 m (1H,
2-H, w1/2 = 7.2 Hz), 5.14 m (1H, 3-H, w1/2 = 7.2 Hz),
5.87 s (1H, 7-H). 13C NMR spectrum (CD3OD), δC,
ppm: 16.26 (C18), 19.54 (C19), 20.16 (C11), 20.93 (C21),
21.20 (C16), 22.42 and 22.82 (MeCO), 25.85 and 27.90
(Me2C), 28.80 (C12), 30.32 (C4), 31.20 (C15), 33.73
(C23), 37.53 (C9), 37.80 (C10), 37.89 (C1), 47.50 (C13),
49.00 (C17), 51.05 (C5), 67.29 (C3), 68.15 (C6′), 68.72
(C2), 74.20 (C5′), 75.90 (C4′), 77.28 (C22), 84.19 (C20),
84.33 (C14), 102.44 (C24), 107.25 (Me2C), 120.64 (C3′),
121.40 (C7), 156.20 (C2′), 164.20 (C8), 170.61 and
170.81 (MeCO), 179.86 (C1′), 203.00 (C6). Mass
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