Synthesis of brassinolide and its biosynthetic precursors using methyl 3-hydroxy-2-methylpropionate

Article abstract of DOI:10.1134/S1068162009020137

Formal synthesis of plant hormones that belong to the group of 24α-methylbrassinosteroids, including brassinolide and its biosynthetic precursors with one hydroxyl group in their side chain, was performed. Stereochemistry of a methyl group at the C24 atom

Full text of DOI:10.1134/S1068162009020137

ISSN 1068-1620, Russian Journal of Bioorganic Chemistry, 2009, Vol. 35, No. 2, pp. 240–249. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © V.A. Khripach, V.N. Zhabinskii, K.V. Parkhimovich, O.V. Gulyakevich, 2009, published in Bioorganicheskaya Khimiya, 2009, Vol. 35, No. 2, pp. 260–269.
Synthesis of Brassinolide and Its Biosynthetic Precursors
Using Methyl 3-Hydroxy-2-Methylpropionate
V. A. Khripach1, V. N. Zhabinskii, K. V. Parkhimovich, and O. V. Gulyakevich
Institute of Bioorganic Chemistry, Belarussian Academy of Sciences, ul. Kuprevicha 5/2, Minsk, 220141 Belarus
Received July 14, 2008; in final form, September 17, 2008
Abstract—Formal synthesis of plant hormones that belong to the group of 24α-methylbrassinosteroids, includ-
ing brassinolide and its biosynthetic precursors with one hydroxyl group in their side chain, was performed.
Stereochemistry of a methyl group at the C24 atom was provided by the choice of the desired enanthiomer of
methyl-3-hydroxy-2-methylpropionate and by the sequence of its conversions into the chiral intermediate that
was necessary for the formation of the C23-C28 fragment of the side chain. The (22R,23R)-diol group was
introduced by the Sharpless asymmetric dihydroxylation of the intermediate ∆22-steroids, the products of con-
secutive reactions of attachment of a low-molecular sulfone to the steroid C22-aldehyde, acetylation, and reduc-
tive desulfurization of the intermediate β-acetoxysulfones. Reduction of 22-acetoxy-23,25-disulfones was
shown to proceed with the preservation of the functional group at atom C22.
Key words: steroids, brassinolide, sulfones, olefination
DOI: 10.1134/S1068162009020137
INTRODUCTION
enzyme catalyzes hydroxylation of the C22 atom of
campesterol and its derivatives with the oxidized cyclic
part [5] (Scheme 1). Further C-23 hydroxylation with
participation of the CYP90A1 cytochrome (EC 1.14)
results in (22R,23R)-diols (III). Chemical methods for
synthesis of all the compounds of probable biosynthetic
chain are obligatory for systematic study of biosyn-
thetic pathways of brassinosteroids. Although, a num-
ber of papers devoted to the preparation of both
22-mono- and 22,23-dihydroxyderivatives of campes-
terol are published now [6–9], a universal synthetic
The side chain of brassinosteroids is the structural
element [1] that significantly affects their biological
activity [2–4].2 Organic chemists consider this element
to be the most difficult in the preparative synthesis of
such compounds, especially in the case of brassinolide
and its analogues.
Brassinolide forms in plants as a result of the trans-
formations (mainly oxidative) of campesterol. The side
chain of compound (I) begins to form from (22S)-alco-
hols (II) by the action of the CYP90B1 enzyme (EC
1.14.13) from the cytochrome P-450 family. This method is still not proposed.
28
OH
OH
(R)
22
24
(S)
(R)
(R)
23 (R)
(S)
25
HO
(III)
(I)
(II)
Scheme 1.
The goal of this study is elaboration of the approach using available starting compounds and common inter-
mediates. Molecules of the target compounds contain
the asymmetric C24 atom, and suitable chiral synthetic
block will be useful for the preparation of the terminal
fragment of their side chain. We decided to study the
possibilities for the use of commercially available (2S)-
3-hydroxy-2-methylpropionate (IV) in addition to our
previously described variations of synthesis of C28-
to preparation of brassinosteroids which contain a par-
tially or completely formed side chain of brassinolide
1
Corresponding author; phone: +375 172-678-647; e-mail: khri-
pach@iboch.bas-net.by
2
Abbreviations: Alk, alkyl; Bn, benzyl; DHP, dihydropyran; Thp,
tetrahydropyranyl; Ts, toluenesulfonyl; mCPBA, m-chloroper-
benzoic acid.
240

SYNTHESIS OF BRASSINOLIDE AND ITS BIOSYNTHETIC PRECURSORS
241
brassinosteroids [8, 10, 11]. We planned to use the Synthesis of both the natural hormone (III) itself, its
attachment of disulfone (V) or sulfone (VI) (Scheme 2) monohydroxylated analogue (II), and their sterol pre-
to the corresponding C22-steroid aldehydes as a key cursor (IX) would be performed by further conversions
reaction for synthesis of all the target brassinosteroids. according to the given retrosynthetic scheme.
OH
X
OAc
PhO2S
⇒
⇒
⇒
SO2Ph
SO2Ph
SO2Ph
(VII)
(II), X = H
(III), X = OH
(V)
2
1
HO
(S)
CO2Me
OAc
3
(ΙV)
PhO2S
⇒
SO2Ph
(IX)
(VIII)
(VI)
Scheme 2.
RESULTS AND DISCUSON
scheme 3. The treatment of alcohol (IV) with dihydro-
propionate, the hydride reduction of ester (X), and the
benzylation of alcohol (XI) gave disubstituted ester
(XII). Protective groups of this compound were intro-
duced according to the principle of orthogonal stability
[12], i.e., every of them could be separately removed in
the presence of the others. For example, the treatment
of compound (XII) with toluenesulfonic acid in metha-
nol resulted in selective removal of tetrahydropyranyl
Both commercially available enanthiomers (R and
S) of 3-hydroxy-2-methylpropionate can theoretically
be applied to the formation of the 24α-methylsterol side
chain typical for brassinolide and its biosynthetic pre-
cursors. The desired stereochemistry of the C24 asym-
metric center can be achieved in the case of the applica-
tion of methyl-(2S)-3-hydroxy-2-methylpropionate
(IV) only under the condition of the final conversion of
the C1 atom of this compound into the C23 atom of the
side chain. We solve this problem as follows from protection and the formation of alcohol (XIII).
DHP
BnBr
NaH
LiAlH4
98%
TsOH
HO
ThpO
OH
ThpO
89%
CO2Me
CO2Me
HO
(IV)
(X)
(XI)
TsOH, MeOH
TsCl, Py
91%
OBn
ThpO
OBn
(XII)
(XIII), 56% from (XI)
PhSH, K2CO3
BnO
OTs
DMF
98%
TsO
BnO
OBn
(XIV)
(XV)
(XIV)
(XVI)
mCPBA
CHCl3
94%
BnO
SO2Ph
SPh
Scheme 3.
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 35 No. 2 2009

242
KHRIPACH et al.
O
O
S
O
(XVI)
BuLi
O
2BuLi
3BuLi
Li
O
S
O
S
BnO
BnO
S
O
O
BnO
BnO
O
O
O
Li
(XVIII)
Li
(XIX)
Li
Li
Li
(XVII)
MeI
2MeI
3MeI
O
S
O
S
O
S
1. BuLi
2. MeI
86%
O
O
O
(XX), 9% from (XVI)
(XXI), 50% from (XVI)
(XXII), 14% from (XVI)
1. BF3 · Et2O, NaI, MeCN
2. H2O
97%
94%
O
HO
S
O
(XXIII)
Scheme 4.
The introduction of two methyl groups in the low fone (XVI). Note that significant amounts of both the
molecular fragment (the terminal methyl groups of the monoalkyl product (XX) and trialkyl product (XXIII)
side chain of the target steroids) was aimed at the prep- were present in the reaction mixture under the reaction
aration of an intermediate with the substituent which conditions optimized for the preparation of the dime-
thyl derivative (XXI). Both side products were used for
the preparation of sulfone (XXIII). Repetitive methyla-
tion of sulfone (XX) gave compound (XXI), whereas a
product of trialkylation (XXII) and a product of dialkyla-
tion (XXI) formed the target sulfone (XXIII) after the
treatment with boron trifluoride etherate.
could effectively stabilize the carbanion center at the
C1 atom. Further, this substituent should easily be
removed on the corresponding stage of the synthesis.
The Phenylsulfonyl group was chosen as such substitu-
ent. It was introduced by the tosylation of alcohol
(XIII), the nucleophilic substitution of the phenylsul-
foxide anion for tosylate (XIV), and the oxidation of
sulfide (XV). All o these reactions proceeded with the
yields closed to quantitative.
The second sulfonyl group was introduced into alco-
hol (XXIII) by the sequence of reactions described
above, including tosylation, the nucleophilic substitu-
tion of phenylsulfide group for tosyl group of com-
pound (XXIV), and the oxidation of sulfide (XXV)
with m-chloroperbenzoic acid (Scheme 5). The sulfone
group in compound (XXV) was selectively removed by
magnesium reduction in methanol. Sulfide (XXVII)
was oxidized by treatment with hydrogen peroxide.
Note that this method of the conversion of sulfides into
sulfones proved to be effective for the studied com-
pounds as well as the use of m-chloroperbenzoic acid
according to the yield of the target product. Moreover,
it was more convenient in practice.
Investigations demonstrated that methylation of sul-
fone (XVI) was a stepwise process that was accompa-
nied by side reactions (Scheme 4). The interaction of
sulfone (XVI) with 1 equivalent of butyl lithium
resulted in the formation of lithium salt (XVII). Fur-
ther, it can react with methyl iodide with the formation
of a product of monoalkylation (XX). The treatment of
sulfone (XVI) with the excess of a base gave dilithium
salt (XVIII). It reacts with two equivalents of methyl
iodide and forms an alkylation product (XXI). In addi-
tion, Ó-attachment of lithium to aromatic cycles is pos-
sible under the reaction conditions [13]. The isolation
The Sharpless asymmetric hydroxylation of ∆22-ste-
of compound (XXII) demonstrated that benzyl residue roids is a standard method for the introduction of a
is mainly involved in this attachment in the case of sul- 22R,23R-diol group in the synthesis of brassinosteroids
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SYNTHESIS OF BRASSINOLIDE AND ITS BIOSYNTHETIC PRECURSORS
243
PhSH, K2CO3
TsCl, Py
99%
DMF
HO
TsO
95%
SO2Ph
SO2Ph
(XXIII)
(XXV)
(XXIV)
mCPBA
CHCl3
PhS
PhO2S
93%
SO2Ph
SO2Ph
(XXVI)
Mg/MeOH
83%
H2O2
94%
PhO2S
PhS
(XXVII)
(XXVIII)
5.
Scheme
OH
OH
Alk
CHO
PhO2S
Alk
Alk
+
Alk
(R)
(S)
1. Ac2O
Li
2. Na/Hg
or Mg/Hg
(XXX)
SO2Ph
SO2Ph
(XXXII)
(XXIX)
(XXXI)
(XXXIII)
2 : 1
Scheme 6.
[1]. Many of these compounds were synthesized by the with the subsequent chromatographic fractionation
interaction of α-sulfonylcarbanions, which were gener- yielded β-hydroxysulfone (XXXV) (Scheme 7). Its
ated from the corresponding sulfones, with C22-alde- acetylation resulted in acetate (XXXVI) that was
hydes [14]. This process is a special case of the Julia- treated with magnesium amalgam in methanol with the
Lythgoe olefination [15] that predominantly or exclu- formation of 22-acetate (XXXVII). The structure of
sively gives trans-olefins. The attachment of the lithium this compound was confirmed by the comparison of its
salt of sulfones (XXX) to steroid aldehydes (XXIX) spectral characteristics with those of the [26,27-2H6]-
proceeds with the formation of the mixture of all four analogue of (XXXVII), which were previously pre-
possible β-hydroxysulfones with predominance of 22R- pared by us through another method [11]. Diol
isomers (XXXI) (Scheme 6). Isolation of such individ- (XXXVIII) can be prepared from acetate (XXXVII) in
ual isomers was reported [16], although the mixture of two stages [11].
isomers (XXXI) and (XXXII) is acetylated. The inter-
Synthesis of (22R,23R)-dihydroxyderivatives can be
mediate acetoxysulfones are further treated with
performed using sulfone (XXVIII) (Scheme 8). The
sodium or magnesium amalgam, and trans-∆22-steroids
interaction of lithium salt of this sulfone with aldehyde
(XXXIX) [19] gave a mixture of β-hydroxysulfones
(XXXIII) are prepared.
The desulfurization of β-hydroxysulfones (XXXI) (XL) that was acetylated without any additional treat-
in the synthesis of brassinosteroids with preservation of ment. The mixture of β-acetoxysulfones (XLI) was
the functional group at the C22 atom is also of interest, reduced with magnesium amalgam. The obtained ∆22-
but no one has successfully performed this reaction olefin (XLII) is a known intermediate in the synthesis
until now. We demonstrated that the introduction of an of castasterone (XLIII) and brassinolide (XLIV) [10].
additional phenylsulfonyl group in the δ-position to
Thus, the described synthetic scheme used methyl
hydroxyl group changed the direction of this reaction
(S)-3-hydroxy-2-methylpropionate (IV) as a chiral part
and gave 22-alcohols instead of the usual olefination
for the creation of the C23-C28-fragment of the side
products.
chain, and allowed synthesis of a number of 24α-meth-
The attachment of the lithium salt of sulfone ylbrassinosteroids beginning from the first representa-
(XXVI) to aldehyde (XXXIV), which was prepared tive of biosynthetic sequence, (22S)-hydroxycampes-
from stigmasterol by a three-step synthesis [17, 18], terol (XXXVIII).
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 35 No. 2 2009

244
KHRIPACH et al.
OH
CHO
OAc
(XXVI)
AcCl
81%
Mg/Hg
67%
BuLi
SO2Ph
SO2Ph
SO2Ph
43%
SO2Ph
OMe
(XXXIV)
(XXXV)
(XXXVI)
OH
OAc
HO
OMe
(XXXVII)
(XXXVIII)
Scheme 7.
CHO
OH
OAc
(XXVIII)
BuLi
Ac2O
Mg/Hg
SO Ph
SO Ph
2
2
O
O
(XXXIX)
(XL)
(XLI)
OH
HO
HO
HO
Z
(XLIII), Z = –
(XLIV), Z = O
H
O
O
O
(XLII), 39% from (XXXIX)
Scheme 8.
EXPERIMENTAL
nance of chloroform that was present in deuterochloro-
form as an impurity (δ 7.26 ppm for proton resonances
and δ 77 ppm for resonances from carbon atoms). Melt-
ing points were determined on a Kofler block (Ger-
many). The reactions were monitored by TLC on DC-
alufolien Kieselgel 60 F254 plates (VWR, Art. 5715). A
column chromatography was performed on a Kieselgel 60
silica gel (VWR, Art. 7734).
The following reagents were used in this study:
methyl (2S)-3-hydroxy-2-methylpropionate, toluene-
sulfonyl chloride, benzyl bromide, m-chloroperbenzoic
acid, thiophenol, methyl iodide, and butyl lithium (Ald-
rich, United States). NMR spectra (δ, ppm; J, Hz) were
recorded on a Bruker Avance 500 spectrometer
(500 MHz for 1ç and 125 MHz for 13C, Germany) in a
solution of CDCl3 (if another solvent is not indicated).
Methyl (2S)-2-methyl-3-(tetrahydro-2H-pyran-
Chemical shifts were determined according to the reso- 2-yloxy)propionate (X). Dihydropyran (1.00 ml,
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SYNTHESIS OF BRASSINOLIDE AND ITS BIOSYNTHETIC PRECURSORS
245
10.4 mmol) and TsOH · H2O (92 mg, 0.49 mmol) were 10 h at 40°ë, mixed with pyridine (5 ml), and evapo-
added to the solution of methyl methylpropionate (IV) rated in a vacuum. The residue was fractionated on a
(0.99 ml, 1.06 g, 8.9 mmol) in anhydrous CH2Cl2 column with silica gel eluted with the mixture of petro-
(10 ml). The reaction mixture was stirred at room tem- leum-ether and ethyl acetate (from 8 : 1 to 3 : 1). Ester
perature for 2.5 h, mixed with pyridine (0.1 ml), and the (XIII) was prepared as an oil with a yield of 11.2 g
1
solvent was evaporated. The residue was fractionated (56%). The spectrum of H NMR: 0.88 (3 H, d, J 7.0,
on a column with silica gel eluted with the mixture of 2-Me), 2.03–2.13 (1 H, m, H2), 2.64 (1 H, m, OH), 3.43
ether and CH2Cl2 (from 20 : 1 to 1 : 10). Ester (X) was (1 H, dd, J 8.0, 9.1, H1 or H3), 3.50 (1 H, dd, J 9.1, 4.7,
isolated as an oil with the yield of 1.62 g (89%). The H1 or H3), 3.57–3.65 (2 H, m, H1 or H3), 4.52 (2 H, s,
1
spectrum of H NMR: 1.17 (1.5 H, dd, J 7.0, 2-Me), PhCH2O), 7.27–7.37 (5 H, m, Ph). The spectrum of
1.18 (1.5 H, dd, J 7.0, 2-Me), 1.47–1.62 (4 H, m, CH2 13C NMR: 13.43, 35.52, 67.80, 73.35, 75.40, 127.57,
of Thp), 1.65–1.70 (1 H, m, CH2 of Thp), 1.74–1.83 127.69, 128.42, 137.97.
(1 H, m, CH2 of Thp), 2.74–2.81 (1 H, m, H2), 3.44
(2R)-3-(Benzyloxy)-2-methylpropyl-4-methyl-
(0.5 H, dd, J 5.9, 9.6, H3), 3.47–3.52 (1 H, m, H3), 3.58
benzene sulfonate (XIV). Tosyl chloride (26.4 g,
(0.5 H, dd, J 7.5, 9.6, H3), 3.683 (1.5 H, s, CO2Me),
138 mmol) was added to the solution of alcohol (XIII)
3.686 (1.5 H, s, CO2Me), 3.75 (0.5 H, dd, J 6.0, 9.6, CH2
(12.6 g, 69.9 mmol) in pyridine (150 ml). The excess of
of Thp), 3.78–3.86 (1 H, m, CH2 of Thp), 3.90 (0.5 H,
tosyl chloride was decomposed four hours later by the
dd, J 7.4, 9.6, CH2 of Thp), 4.60 (1 H, m, CH of Thp).
addition of water (5 ml) to the reaction mixture. Ten
The spectrum of 13C NMR: 14.01,19.09, 19.31, 25.40,
minutes later, the reaction mixture was diluted with
30.40, 30.47, 40.01, 40.19, 51.62, 61.78, 62.09, 69.00,
water (200 ml) and extracted with chloroform (3 ×
69.35, 98.40, 99.03, 175.29, 175.38.
200 ml). The joined organic phase was dried over
(2R)-2-Methyl-3-(tetrahydro-2H-pyran-2-yloxy)pro-
pane-1-ol (XI). Ester (X) (1.62 g, 8.03 mmol) was dis-
solved in ether (20 ml) and cooled by ice. LiAlH4
(0.97 g, 25.6 mmol) was added in small portions to the
solution during the cooling. The reaction mixture was
stirred for 2 h at room temperature; water (1.0 ml), 15%
aqueous solution of NaOH (1.0 ml), and water (3 ml)
again were added dropwise. The precipitate was filtered
and washed with ether. The filtrate was evaporated. The
residue was fractionated on a column with silica gel
eluted with the mixture of petroleum-ether and ethyl
acetate (from 10 : 1 to 2 : 1). Alcohol (XI) was prepared
as an oil with a yield of 1.37 g (98%). The spectrum of
1H NMR: 0.87 (1.5 H, dd, J 6.8, 2-Me), 0.89 (1.5 H, dd,
J 6.8, 2-Me), 1.46–1.61 (4 H, m, CH2 of Thp), 1.66–
1.82 (2 H, m, CH2 of Thp), 1.98–2.06 (1 H, m, H2), 2.77
(1 H, broadened s, OH), 3.30–3.90 (6 H, m, H1, H3,
and CH21o3f Thp), 4.56 (1 H, m, CH of Thp). The spec-
trum of C NMR: 13.42, 13.53, 19.57, 25.25, 25.28,
30.50, 30.55, 35.34, 35.59, 62.43, 62.49, 67.23, 67.27,
71.98, 72.08, 76.75, 77.00, 77.25, 99.02, 99.30.
(2S)-3-Benzyloxy-2-methylpropane-1-ol (XIII).
NaH (80% suspension in oil, 5.63 g, 0.188 mol) was
added to the solution of alcohol (XI) (13.2 g,
75.9 mmol) in anhydrous tetrahydrofurane (500 ml)
during intensive stirring. The reaction mixture was
stirred for 10 min, and benzyl bromide (38.7 ml,
0.33 mol) and tetrabutylammonium iodide (39.9 g,
0.108 mol) were added. The reaction mixture was
stirred for 4 days at room temperature. Ethanol (10 ml)
and, then, NH4Cl (15 g) were added. The reaction mix-
ture was diluted with water (200 ml) and extracted with
ethyl acetate (3 × 200 ml). The joined organic phase was
dried over Na2SO4, and the filtrate was evaporated in a
vacuum. The residue was filtered through a layer of sil-
Na2SO4 and evaporated in a vacuum. The residue was
fractionated on a column with silica gel eluted with the
mixture of petroleum-ether and ethyl acetate (from
20 : 1 to 3 : 1). Tosylate (XIV) was prepared with a
yield of 21.3 g (91%) mp 27–28°C (hexane). The spec-
trum of 1H NMR: 0.94 (3 H, d, J 6.9, 2-Me), 2.07–2.16
(1 H, m, H2), 2.42 (3 H, s, OTs), 3.30–3.37 (2 H, m,
H3), 3.99 (1 H, d, J 5.7, 9.4, H1), 4.04 (1 H, dd, J 5.7,
9.4, H1), 4.40 (2 H, s, PhCH2–O), 7.22–7.25 (2 H, m,
Ar), 7.27–7.35 (5 H, m, Ar), 7.78 (2 H, d, J 8.3, Ar). The
spectrum of 13C NMR: 13.59, 21.59, 33.63, 71.04,
72.19, 73.02, 127.39, 127.53, 127.88, 128.30, 129.76,
132.95, 138.16, 144.62.
Benzyl-(2R)-methyl-3-phenylthiopropyl ester (XV).
Potassium carbonate (13.3 g, 96.4 mmol) and thiophe-
nol (8.85 ml, 10.6 g, 96.4 mmol) were added to the
solution of tosylate (XIV) (21.3 g, 63.7 mmol) in dim-
ethylformamide (210 ml). The reaction mixture was
stirred for 2 h at room temperature, diluted with 5%
aqueous solution of KOH (400 ml), and extracted with
chloroform (3 × 100 ml). The joined organic phase was
dried over Na2SO4 and the solvent was evaporated in a
vacuum. The residue was fractionated on a column with
silica gel eluted with the mixture of petroleum-ether
and ethyl acetate (from 100 : 1 to 10 : 1). Sulfide (XV)
was prepared as an oil with a yield of 17.0 g (98%). The
spectrum of 1H NMR: 1.06 (3 H, d, J 6.8, 2-Me), 2.03–
2.12 (1 H, m, H2), 2.79 (1 H, dd, J 13.0, 7.4, H1), 3.16
(1 H, dd, J 13.0, 5.7, H1), 3.40–3.45 (2 H, m, H3), 4.47
(2 H, s, O–CH2–Ph), 7.14 (1 H, t, J 7.4, Ph), 7.23–7.36
(9 H, m, Ph). The spectrum of 13C NMR: 16.73, 33.78,
37.42, 72.99, 74.00, 125.56, 127.47, 128.31, 128.72,
128.79, 137.17, 138.49.
(2R)-3-(Benzyloxy)-2-methylpropylphenylsulfone
ica gel and evaporated. The obtained product was dis- (XVI). Sulfide (XV) (17.0 g, 62.4 mmol) was dissolved
solved in methanol (550 ml) and mixed with TsOH · in chloroform (300 ml) and mCPBA (42.8 g, 77%,
H2O (2.20 g, 11.6 mmol). The mixture was kept for 0.191 mol) was added on ice-cooling. The reaction
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 35 No. 2 2009

246
KHRIPACH et al.
mixture was stirred for 4 h at room temperature, alkali- The spectrum of 1H NMR: 0.99 (1.8 H, d, J 9.3, 1-Me),
fied to pH 7 with 25% NH4OH, and diluted with water 1.19 (3 H, dd, J 7.1, 2.2, 2-Me), 1.24 (1.2 H, d, J 9.3,
(400 ml). The organic phase was separated and water 1-Me), 2.41–2.49 (0.4 H, m, H2), 2.66–2.74 (0.6 H, m,
phase was washed with petroleum-ether (4 × 100 ml). H2), 3.18–3.25 (1 H, m, H3), 3.34 (0.6 H, dd, J 9.8, 5.2,
The joined organic phase was dried over Na2SO4 and H1), 3.43–3.47 (1 H, m, H3), 3.78 (0.4 H, dd, J 9.3, 5.2,
evaporated in a vacuum. The residue was fractionated H1), 4.35–4.53 (2 H, m, PhCH2–O), 7.23–7.37 (5 H, m,
on a column with silica gel eluted with the mixture of Ph), 7.52–7.57 (2 H, m, Ph), 7.62–7.66 (1 H, m, Ph),
13
ether and ethyl acetate (from 10 : 1 to 3 : 1). Sulfone 7.84–7.91 (2 H, m, Ph). The spectrum of C NMR:
(XVI) was prepared as an oil with a yield of 17.9 g 7.39, 11.00, 11.09, 15.85, 30.99, 33.93, 59.44, 62.32,
1
(94%). The spectrum of H NMR: 1.12 (3 H, d, J 6.8, 71.77, 72.40, 72.61, 73.10, 127.49, 127.59, 127.66,
2-Me), 2.35–2.44 (1 H, m, H2), 2.93 (1 H, dd, J 14.1, 128.24, 128.32, 128.36, 128.54, 128.62, 129.06,
8.0, H1), 3.31 (1 H, dd, J 9.3, 6.4, H1), 3.40–3.43 (2 H, 130.39, 133.38, 133.42, 137.99, 138.54.
m, H3), 4.38–4.44 (2 H, m, PhCH2–O), 7.23–7.35 (5 H,
Methylation of sulfone (XX). The 2.3 M solution
m, Ph), 7.53–7.57 (2 H, m, Ph), 7.62–7.66 (1 H, m, Ph),
of butyl lithium (1.75 ml, 4.03 mmol) in hexane was
13
7.90–7.93 (2 H, m, Ph). The spectrum of C NMR:
added to the solution of sulfone (XX) (1.10 g,
17.16, 29.38, 59.23, 72.84, 73.51, 127.48, 127.61,
3.54 mmol) in tetrahydrofurane (30 ml) in an argon
127.81, 128.33, 129.22, 133.51, 138.05, 140.01.
atmosphere during stirring at the temperature range of
Methylation of sulfone (XVI). The 2.35 M solution
of butyl lithium (36 ml, 84.5 mmol) in hexane was
added to the solution of sulfone (XVI) (10.3 g,
33.8 mmol) in tetrahydrofurane (240 ml) in a two-
necked flask (internal thermometer, septum) in an
argon atmosphere during stirring at a temperature range
of –70°ë to –45°ë. The solution of methyl iodide
(5.5 ml, 12.5 g, 87.9 mmol) in tetrahydrofurane (30 ml)
was added to the reaction mixture at a temperature
range of –45°ë to –30°ë, 30 min later. After 15 min, the
cooling bath was removed, and the temperature of the
reaction mixture was allowed to rise to –10°ë. NH4Cl
(5 g) was added, the reaction mixture was stirred for
5 min, filtered through a layer of silica gel, and evapo-
rated in a vacuum. The residue was fractionated on a
column with silica gel eluted with the mixture of petro-
leum-ether and ethyl acetate (from 20 : 1 to 3 : 1) and
the following compounds were isolated in the course of
elution:
–60°C to –45°C. The solution of methyl iodide
(0.25 ml, 4.02 mmol) in tetrahydrofurane (0.75 ml) was
added to the reaction mixture at a temperature interval
of –45°C to –30°C, 20 min later. Cooling was stopped
after 15 min, the reaction mixture was allowed to be
heated to –10°ë, and NH4Cl (1.2 g) was added. The
reaction mixture was stirred for 5 min, filtered through
a layer of silica gel, and evaporated in a vacuum. The
residue was fractionated on a column with silica gel
eluted with the mixture of petroleum-ether and ethyl
acetate (from 20 : 1 to 3 : 1). The oily product was iso-
1
lated with a yield of 990 mg (86%). Its H NMR and
13C NMR spectra were identical to those of sulfone
(XXI).
(2R)-2,3-Dimethyl-3-(phenylsulfonyl)butane-1-
ol (XXIII) Sodium iodide (9.72 g, 64.8 mmol) was
added to the solution of ester (XXI) (10.66 g,
32.07 mmol) in acetonitrile (215 ml). The solution of
boron trifluoride etherate (12.2 ml) in acetonitrile
(100 ml) was added to the reaction mixture drop-wise
within 15 min during stirring and ice cooling. The reac-
tion mixture was stirred for 30 min during ice cooling
and for 6 h at room temperature, poured out in ice-water
(250 ml), and extracted with methylene chloride (4 ×
100 ml). The joined organic phase was dried over
Na2SO4 and the solvent was evaporated in a vacuum.
The residue was fractionated on a column with silica
gel eluted with the mixture of hexane and ethyl acetate
(from 10 : 1 to 1 : 1). The alcohol (XXIII) was prepared
with the yield of 7.53 g (97%); mp 78–82°ë (hexane–
ethyl acetate). The spectrum of 1H NMR: 1.16 (3 H, d,
J 7.1, 2-Me), 1.26 (3 H, s, H4 or 3-Me), 1.31 (3 H, s, H4
or 3-Me), 2.17-2.23 (1 H, m, H2), 2.38 (1 H, broadened
s, OH), 3.70-3.76 (1 H, m, H1), 3.94-3.99 (1 H, m, H1),
7.54-7.57 (2 H, m, Ph), 7.63-7.67 (1 H, m, Ph), 7.86-
(2R)-1,1,2-Trimethyl-3-[(2-methylbenzyl)oxy]pro-
pylphenylsulfone (XXII) as an oil with a yield of
1.69 g (14%). The spectrum of 1H NMR: 1.22 (3 H, d,
J 7.0, 2-Me), 1.29 (3 H, s), 1.31 (3 H, s), 2.42–2.47
(1 H, m, H2), 2.72 (3 H, s, CH3C6H4–), 4.49 (2 H, m,
−OCH2C6H4CH3), 7.28–7.90 (9 H, m, aromatic). The
spectrum of 13C NMR: 14.18, 19.85, 20.76, 21.30, 36.55,
67.18, 72.69, 73.09, 126.10, 127.50, 128.31, 130.39,
133.04, 133.21, 133.36, 134.58, 138.43, 140.40.
(2R)-3-(Benzyloxy)-1,1,2-trimethylpropylphenyl-
sulfone (XXI) with the yield of 5.62 g (50%); mp 86–
87°ë (hexane). The spectrum of 1H NMR: 1.21 (3 H, d,
J 6.9, 2-Me), 1.30 (3 H, s, 1-Me), 1.31 (3 H, s, 1-Me),
2.29–2.35 (1 H, m, H2), 3.48 (1 H, dd, J 9.4, 6.8, H3),
3.80 (1 H, dd, J 9.4, 3.5, H3), 4.45–4.51 (2 H, m,
PhCH2–O), 7.26–7.36 (5 H, m, Ph), 7.52–7.56 (2 H, m,
Ph), 7.62–7.66 (1 H, m, Ph), 7.84–7.87 (2 H, m, Ph).
The spectrum of 13C NMR: 14.06, 19.93, 20.70, 36.95,
65.78, 72.54, 73.08, 127.50, 128.31, 128.71, 130.39,
133.43, 136.36, 138.39.
13
7.89 (2 H, m, Ph). The spectrum of C NMR: 13.64,
19.49, 22.18, 39.73, 64.75, 65.76, 128.77, 130.45,
133.61, 136.10.
Alcohol (XXIII) was prepared according to the
analogous procedure from ester (XXII) with a yield of
(2R)-3-(Benzyloxy)-1,2-dimethylpropylphenyl-
sulfone (XX). with the yield of 969 mg (9%) as an oil. 94%.
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SYNTHESIS OF BRASSINOLIDE AND ITS BIOSYNTHETIC PRECURSORS
247
(2R)-2,3-Dimethyl-3-(phenylsulfonyl)butyl-4- to 5 : 1). Sulfone (XXVI) was prepared as an oil with a
methylbenzenesulfonate (XXIV). Tosyl chloride yield of 837 mg (93%). The spectrum of 1H NMR: 1.17
(14.8 g, 77.8 mmol) was added to the solution of alco- (3 H, s, H4 or 3-Me), 1.27 (3 H, s, H4 or 3-Me), 1.31
hol (XXIII) (8.58 g, 35.4 mmol) in pyridine (200 ml). (3 H, d, J 6.9, 2-Me), 2.64-2.71 (1 H, m, H2), 2.97 (1 H,
Water (10 ml) was added to the reaction mixture drop- dd, J 14.0, 10.4, H1), 4.31 (1 H, d, J 14.0, H1), 7.53-
wise 20 min later for the decomposition of the excess of 7.56 (2 H, m, Ph), 7.58-7.61 (2 H, m, Ph), 7.64-7.70
tosyl chloride. After 10 min, the reaction mixture was (2 H, m, Ph), 7.82-7.84 (2 H, m, Ph), 7.92-7.94 (2 H, m,
13
diluted with water (200 ml) and extracted with chloro- Ph). The spectrum of C NMR: 16.12, 17.06, 22.66,
form (3 × 200 ml). The joined organic phase was dried 32.65, 58.69, 64.89, 128.07, 128.90, 129.34, 130.54,
over Na2SO4 and the solvent was evaporated in a vac- 133.75, 133.87, 135.43, 139.85.
uum. The residue was fractionated on a column with a
(2S)-2,3-Dimethylbutylphenylsulfide (XXVII).
silica gel eluted with the mixture of petroleum-ether
Magnesium (1.52 g, 63.0 mmol) was added to the solu-
and ethyl acetate (from 20 : 1 to 3 : 1). Tosylate (XXIV)
tion of sulfonyl sulfide (XXV) (2.43 g, 7.26 mmol) in
was prepared with a yield of 13.9 g (99%) as an oil. The
absolute methanol (150 ml) during intensive stirring.
spectrum of 1H NMR: 1.12 (3 H, d, J 6.9, 2-Me), 1.23
The reaction mixture was stirred for 3 h at 40°ë. The
(3 H, s, H4 or 3-Me), 1.24 (3 H, s, H4 or 3-Me), 2.31-
precipitate was filtered off. The filtrate was neutralized
2.37 (1 H, m, H2), 2,45 (3 H, s, OTs), 4.06 (1 H, dd,
with 3 N HCl to pH 7 and extracted with petroleum-
J 9.9, 7.5, H1), 4.52 (1 H, dd, J 9.9, 3.5, H1), 7.36 (2 H,
ether (3 × 50 ml). The joined organic extract was dried
d, J 8.0, aromatic), 7.53 (2 H, t, J 7.5, aromatic), 7.63-
over Na2SO4 and the solvent was evaporated in a vac-
7.67 (1 H, m, aromatic), 7.76-7.81 (4 H, m, aromatic).
uum. The residue was fractionated on a column with a
The spectrum of 13C NMR: 13.25, 18.87, 21.64, 36.71,
silica gel eluted with the mixture of petroleum-ether
64.96, 72.25, 127.93, 128.87, 129.91, 130.37, 132.72,
and ethyl acetate (20 : 1). Sulfide (XXVII) was isolated
133.79, 135.57, 144.92.
as an oil with a yield of 1.18 g (83%). The spectrum of
1H NMR: 0.85 (3 H, d, J 6.8), 0.90 (3 H, d, J 6.9), 0.96
(3 H, d, J 6.8), 1.57–1.66 (1 H, m, H3), 1.74–1.80 (1 H,
m, H2), 2.70 (1 H, dd, J 8.5,12.4, H1), 3.03 (1 H, m,
H1), 7.12–7.17 (2 H, m, Ph), 7.23–7.28 (1 H, m, Ph),
(2R)-1,1,2-Trimethyl-3-(phenylthio)propylphe-
nyl sulfone (XXV). Potassium carbonate (7.22 g,
52.2 mmol) and thiophenol (5.37 ml, 6.43 g, 58.4 mmol)
were added to the solution of tosylate (XXIV) (13.9 g,
35.1 mmol) in dimethylformamide (80 ml). The reac-
tion mixture was stirred for 2.5 h at room temperature,
diluted with 5% aqueous solution of KOH (300 ml),
and extracted with chloroform (3 × 200 ml). The joined
extract was dried over Na2SO4 and the solvent was
evaporated in vacuum. The residue was fractionated on
a column with silica gel eluted with the mixture of
petroleum-ether and ethyl acetate (from 20 : 1 to 3 : 1).
Sulfonyl sulfide (XXV) was prepared as an oil with a
yield of 10.9 g (95%). The spectrum of 1H NMR: 1.21
(3 H, dd, J 0.7, 6.8, 2-Me), 1.23 (3 H, s, 1-Me), 1.33
(3 H, s, 1-Me), 2.15-2.22 (1 H, m, H2), 2.61 (1 H, dd,
J 13.0, 11.1, H3), 3.88 (1 H, dd, J 0.8, 2.3, 12.9, 1.5,
H3), 7.20-7.23 (1 H, m, Ph), 7.28-7.32 (2 H, m, Ph),
7.41-7.43 (2 H, m, Ph), 7.46-7.50 (2 H, m, Ph), 7.59-
7.63 (1 H, m, Ph), 7.71-7.74 (2 H, m, Ph). The spectrum
of 13C NMR: 14.92, 18.00, 21.96, 37.42, 37.58, 66.18,
126.33, 128.74, 128.91, 130.22, 130.34, 133.47,
136.17.
13
7.30–7.34 (2 H, m, Ph). The spectrum of C NMR:
15.07, 17.68, 20.25, 31.38, 38.34, 38.80, 125.46,
128.66, 128.74, 128.90. The spectral characteristics of
sulfide (XXVII) correlated with those published in the
literature [20].
(2S)-2,3-Dimethylbutylphenylsulfone (XXVIII).
The 30% hydrogen peroxide (60 ml) was added drop-
wise to the solution of sulfide (XXVII) (2.26 g,
11.6 mmol) in glacial acetic acid (60 ml) on stirring.
The reaction mixture was stirred for 17 h at room tem-
perature, diluted with water (50 ml), and extracted with
petroleum-ether (3 × 50 ml). The joined organic phase
was washed with the saturated solution of NaHCO3 and
dried over Na2SO4. The solvent was evaporated to 1/3
of the initial volume; the residue was filtered through a
layer of silica gel and evaporated. Sulfone (XXVIII)
was prepared as an oil with a yield of 2.5 g (94%). The
spectrum of 1H NMR: 0.76 (3 H, d, J 6.8), 0.81 (3 H, d,
J 6.8), 1.01 (3 H, d, J 6.9), 1.63–1.70 (1 H, m, H3),
1.97–2.05 (1 H, m, H2), 2.87 (1 H, dd, J 8.8, 14.1, H1),
3.08 (1 H, dd, J 3.3, 14.1, H1), 7.54–7.58 (2 H, m, Ph),
7.62–7.66 (1 H, m, Ph), 7.89–7.92 (2 H, m, Ph). The
spectrum of 13C NMR: 15.89, 17.81, 19.10, 32.37,
33.74, 60.45, 127.83, 129.22, 133.48, 140.06. The
spectral characteristics of sulfone (XXVIII) correlated
with those published in the literature [20].
(2R)-2,3-Dimethyl-1,3-bis(phenylsulfonyl)butane
(XXVI). Sulfonyl sulfide (XXV) (822 mg, 2.46 mmol)
was dissolved in chloroform (50 ml) and mCPBA
(822 mg, 77%, 7.45 mmol) was added to the solution
during ice cooling. The reaction mixture was stirred for
5 h at room temperature, neutralized with 25% aqueous
solution of NH4OH to pH 7, and diluted with water
(40 ml). The organic phase was separated in a separat-
ing funnel, and the aqueous phase was washed with
(22R,24R)-23,25-Bis(phenylsulfonyl)-6b-methoxy-
chloroform (4 × 20 ml). The joined organic extract was 24-methyl-3a,5-cyclo-5a-cholestane-22-ol (XXXV).
dried over Na2SO4 and evaporated in a vacuum. The res- The 2.2 M solution of butyl lithium (0.8 ml, 0.65 mmol)
idue was fractionated on a column with silica gel eluted in hexane was added to the solution of disulfone
with the mixture of toluene and ethyl acetate (from 50 : 1 (XXVI) (128 mg, 0.35 mmol) in tetrahydrofurane
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 35 No. 2 2009

248
KHRIPACH et al.
(4 ml) at –50°ë in the argon atmosphere during stirring. (30 ml) cooled to 0°ë during stirring. The reaction mix-
The reaction mixture was stirred for 30 min at –50°ë ture was stirred for 1 h at 0°ë and filtered through a
and cooled to –78°ë, and the solution of aldehyde layer of silica gel. The filtrate was diluted with water
(XXXIV) (100 mg, 0.29 mmol, prepared according to (15 ml) and extracted with petroleum-ether (3 × 10 ml).
the procedure {17, 18]) in tetrahydrofurane (1 ml) was The organic extracts were dried over Na2SO4 and the
added. The reaction mixture was stirred at −78°ë for solvent was evaporated in a vacuum. The residue was
3 h, the cooling was removed, and the reaction mixture fractionated on a column with silica gel eluted with the
was gradually brought up to room temperature and mixture of petroleum-ether and ethyl acetate (from 20 : 1
mixed with the saturated solution of NH4Cl (5 ml). The to 10 : 1). Acetate (XXXVII) was prepared as an oil
aqueous phase was separated from the organic phase with a yield of 9.0 mg (67%). The spectrum of
and washed with ethyl acetate (3 × 5 ml). The joined 1H NMR: 0.42 (1 H, dd, J 5.1, 7.9), 0.63 (1 H, dd, J 4.1,
organic phase was dried over Na2SO4 and evaporated in 4.7), 0.71 (3 H, s, H18), 0.87 (3 H, d, J 7.3), 0.88 (3 H,
a vacuum. The residue was fractionated on a column d, J 7.3), 0.95 (3 H, d, J 6.8), 1.06 (3 H, s, H19), 2.03
with silica gel eluted with the mixture of petroleum- (3 H, s, OAc), 2.75 (1 H, t, J 2.7), 3.31 (3 h, s, OMe),
ether and ethyl acetate (from 15 : 1 to 3 : 1). Compound 5.14 (1 H, m, H22). The spectrum of 13C NMR: 12.00,
(XXXV) was prepared as an oil with a yield of 90 mg 12.69, 13.01, 13.99, 19.26, 21.21, 21.48, 22.64, 22.76,
1
(43%). The spectrum of H NMR: 0.60 (3 H, s, H18), 24.10, 24.93, 28.06, 28.18, 29.67, 30.48, 31.88, 33.33,
0.97 (3 H, s, H19), 1.51 (3 H, s, H26 or H27), 1.54 (3 H, 34.89, 35.27, 38.98, 40.21, 42.65, 43.32, 47.96, 52.66,
d, J 7.3, H28), 1.65 (3 H, s, H26 or H27), 2.74 (1 H, t, 56.39, 56.54, 76.31, 82.35, 170.93.
J 2.8, H6), 3.30 (3 H, s, OMe), 3.84 (1 H, dd, J 2.6, 7.5,
(24S)-6-(1,3-Dioxolane-2-yl)-24-methyl-3a,5-cyclo-
H22), 3.99 (1 H, s, H23), 7.55–7.63 (2 H, m, Ph), 7.65–
5a-cholest-22-ene (XLII). The solution of sulfone
7.70 (1 H, m, Ph), 7.91–7.96 (2 H, m, Ph). The spec-
(XXVIII) (250 mg, 1.1 mmol) in anhydrous tetrahydro-
13
trum of C NMR: 12.43, 13.02, 14.11, 14.28, 15.02,
furane (9 ml) was cooled to –60°ë and mixed with
19.23, 21.22, 21.49, 21.63, 22.61, 24.44, 24.92, 27.43,
2.2 N solution of butyl lithium (0.6 ml, 1.32 mmol) in
30.29, 33.29, 34.60, 34.84, 35.23, 39.79, 39.87, 43.29,
hexane in an argon atmosphere during stirring. The
43.53, 47.77, 51.77, 55.98, 56.50, 65.58, 67.10, 73.63,
reaction mixture was stirred for 30 min at –60°ë and
82.35, 128.37, 128.85, 129.39, 130.72, 133.77, 133.86,
cooled to –78°ë, and aldehyde (XXXIX) (prepared
136.25, 139.47.
according to the procedure [19], 345 mg, 0.93 mmol) in
(22R,24R)-23,25-Bis(phenylsulfonyl)-22-acetoxy-
6b-methoxy-24-methyl-3a,5-cyclo-5a-cholestane
(XXXVI). The solution of pyridine (2.9 ml, 3.6 mmol)
in CH2Cl2 (0.27 ml), the solution of acetyl chloride
(2.5 ml, 3.5 mmol) in CH2Cl2 (0.24 ml), and 4-(dimeth-
ylamino)pyridine (0.5 mg) were added to the solution
of hydroxysulfone (XXXV) (24 mg, 34 mmol) in
CH2Cl2 (1 ml). The reaction mixture was kept for 24 at
room temperature and diluted with water (2 ml). The
organic phase was separated from the water phase, and
the latter was extracted with CH2Cl2 (3 × 2 ml). The
organic phases were dried over Na2SO4, and the solvent
was evaporated. Acetate (XXXVI) was prepared as an
oil with a yield of 20 mg (81%). The spectrum of
1H NMR: 0.64 (3 H, s, H18), 0.74 (3 H, d, J 6.7, H21),
0.97 (3 H, s, H19), 1.47 (3 H, s, H26 or H27), 1.61 (3 H,
d, J 7.3 H28), 1.63 (3 H, s, H26 or H27), 2.19 (3 H, s,
OAc), 2.74 (3 H, T, J 2.8 H6), 3.30 (3 H, s, OMe), 4.08
(1 H, s, H23), 5.14 (1 H, d, J 7.7, H22), 7.54–7.62 (2 H,
m, Ph), 7.63–7.71 (1 H, m, Ph), 7.92–7.98 (2 H, m, Ph).
The spectrum of 13C NMR: 11.87, 13.05, 14.41, 15.46,
19.20, 21.33, 21.42, 21.50, 22.14, 22.68, 24.77, 24.95,
28.27, 29.70, 30.36, 33.35, 34.93, 35.27, 39.95, 43.30,
43.85, 47.77, 51.87, 55.86, 56.50, 64.02, 67.04, 74.31,
82.36, 128.81, 129.12, 129.33, 130.83, 133.69, 133.77,
136.31, 139.58, 170.17.
anhydrous tetrahydrofurane (5 ml) was added. The
reaction mixture was stirred for 2 h at −78°ë and mon-
itored by TLC. After the disappearance of the starting
aldehyde (XXXIX), acetic anhydride (0.3 ml,
3.2 mmol) was added at –78°ë. The reaction mixture
was gradually brought up to room temperature, kept
under these conditions for 18 h, and diluted with the
saturated solution of NH4Cl (10 ml). The organic phase
was separated, and the water phase was extracted with
ethyl acetate. The joined organic phase was dried over
Na2SO4, and the solvent was evaporated in a vacuum.
The obtained acetoxysulfone (XLI) (0.64 g) was dis-
solved in absolute methanol (50 ml) and cooled to 0°ë.
Magnesium (0.5 g, 20.6 mmol) and HgCl2 (0.2 g,
0.74 mmol) were added to the solution during intensive
stirring. The reaction mixture was heated to room tem-
perature, intensively stirred for 5.5 h, and filtered
through a layer of silica gel. The filtrate was diluted
with water (40 ml) and extracted with petroleum-ether
(4 × 20 ml). The extracts were dried over Na2SO4, and
the solvents were evaporated in a vacuum. The residue
was fractionated on a column with silica gel eluted with
the mixture of petroleum-ether and ethyl acetate
(10 : 1). Olefin (XLII) was prepared as an oil with a
yield of 166 mg (39%) relatively to aldehyde
1
(XXXIX). The spectrum of H NMR: 0.32 (1 H, t,
(22S,24R)-22-Acetoxy-6b-methoxy-24-methyl-3a,5- J 4.2), 0.60 (1 H, dd, J 4.6, 8.1), 0.72 (3 H, s, H18), 0.81
cyclo-5a-cholestane (XXXVII). Magnesium (0.58 g, (3 H, d, J 6.8), 0.82 (3 H, d, J 6.8), 0.90 (3 H, d, J 6.9),
23.6 mmol) and mercury (II) chloride (0.23 g, 0.99 (3 H, d, J 6.8), 1.00 (3 H, s, H19), 3.74 (1 H, q,
0.86 mmol) were added to the solution of disulfone J 6.4, dioxolan), 3.84 (1 H, dd, J 4.6, 12.4, dioxolan),
(XXXVI) (20 mg, 28 mmol) in absolute methanol 3.90 (1 H, td, J 6.4, 8.0, dioxolan), 4.02 (1 H, td, J 6.4,
RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY Vol. 35 No. 2 2009

SYNTHESIS OF BRASSINOLIDE AND ITS BIOSYNTHETIC PRECURSORS
249
7. Nagano, H., Matsuda, M., andYajima, T., J. Chem. Soc.,
Perkin Trans. 1, 2001, pp. 174–182.
8. Khripach, V.A., Zhabinskii, V.N., Antonchik, A.P., Kon-
stantinova, O.V., and Schneider, B., Steroids, vol. 67,
pp. 1101–1108.
7.7, dioxolan), 5.15 (2 H, m, H22 and H23). The spec-
trum of 13C NMR: 7.25, 12.33, 18.02, 18.96, 19.63,
20.14, 20.96, 22.57, 23.03, 24.19, 24.89, 28.83, 33.19,
34.09, 39.23, 40.00, 40.17, 40.28, 42.70, 43.03, 45.59,
47.43, 56.02, 56.36, 64.60, 64.84, 109.89, 131.79,
136.04.
9. Zhabinskii, V.N., Khripach, V.A., and Olkhovik, V.K.,Zh.
Org. Khim., 1996, vol. 32, pp.327–383.
10. Khripach, V.A., Zhabinskii, V.N., Olkhovik, V.K., and
Lakhvich, F.A., Zh. Org. Khim., 1990, vol. 26, pp. 1966–
1976.
ACKNOWLEDGMENTS
The study was supported by the Belarussian Foun-
dation for Basic Research, projects no. X06P-151,
X08P-031, and X08P-064.
11. Antonchik, A.P., Schneider, B., Zhabinskii, V.N., and
Khripach, V.A., Steroids, 2004, vol. 69, pp. 617–628.
12. Wuts, P.G.M. and Greene, T.W., Protective Groups in
Organic Synthesis, New Jersey: John Wiley & Sons, Inc.,
2007.
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