New synthesis of syn-stereodiad building block for polyketides. Formal synthesis of arenamides A and C

Article abstract of DOI:10.1134/S107042801504020X

Abstract An efficient procedure has been developed for the transformation of (7S)-7-(3-bromoprop-1-en-2-yl)-5,5-dimethyl-4,6-dioxaspiro[2.5]octane [available from diethyl (S)-malate] into methyl 2-[(4S)-2,2-dimethyl-5-methylidene-1,3-dioxan-4-yl]acetate,

Full text of DOI:10.1134/S107042801504020X

ISSN 1070-4280, Russian Journal of Organic Chemistry, 2015, Vol. 51, No. 4, pp. 582–590. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © D.G. Shklyaruck, 2015, published in Zhurnal Organicheskoi Khimii, 2015, Vol. 51, No. 4, pp. 599–606.
New Synthesis of syn-Stereodiad Building Block for Polyketides.
Formal Synthesis of Arenamides A and C
D. G. Shklyaruck
Belarusian State University, pr. Nezavisimosti 4, Minsk, 220030 Belarus
e-mail: denis.shklyaruck@gmail.com
Received January 6, 2015
Abstract—An efficient procedure has been developed for the transformation of (7S)-7-(3-bromoprop-1-en-2-
yl)-5,5-dimethyl-4,6-dioxaspiro[2.5]octane [available from diethyl (S)-malate] into methyl 2-[(4S)-2,2-di-
methyl-5-methylidene-1,3-dioxan-4-yl]acetate, and conditions for diastereoselective reduction of the double
C=C bond in the latter have been optimized. The reduction product has been converted into (3S,4S)-3-[tert-
butyl(dimethyl)siloxy]-4-methyldecanoic acid which is a building block for the synthesis of arenamides A and
C, natural compounds possessing pronounced antitumor activity and efficiently inhibiting nitrogen(II) oxide
and prostaglandin E2 (PGE2).
DOI: 10.1134/S107042801504020X
In recent time much attention is given to the isola-
tion of complex compounds from marine organisms
and biological assay of these compounds in order to
reveal structures promising from the viewpoint of
treatment of malignant tumors. Such compounds are
represented mainly by macrocyclic lactones, lactides,
oligopeptides, and depsipeptides (macrolides consist-
ing of hydroxy and amino acid units) [1–9].
1c) or (3S,4S)-3-hydroxy-4-methyloctanoic acid resi-
due (1b). The relative syn configuration of the C28–C29
fragment in molecules 1a–1c was determined on the
basis of the NOE data. The absolute configuration
(28S,29S) was determined by Mosher’s method and was
later confirmed by independent synthesis of 28-epi-,
29-epi-, and 28,29-di-epi-arenamides A [11, 12] and
total syntheses of arenamides A, B, and C [13].
Asolkar et al. [10] isolated three depsipetides, aren-
amide A (1a), arenamide B (1b), and arenamide C (1c),
from the marine bacteria Salinispora arenicola CNT-
088 and studied their biological activity [10]. Mole-
cules 1a–1c are 19-membered macrocycles consisting
of Gly–Val–Leu–Ala–Phe/Met pentapeptide and a syn-
stereodiad,* (3S,4S)-3-hydroxy-4-methyldecanoic (1a,
Arenamides A and B showed dose- and time-
dependent inhibition of TNF-induced NF-κB activity
with IC50 values of 3.7 and 1.7 μmol/L, respectively. In
addition, these compounds inhibited production of
nitric oxide and prostaglandin E2 (PGE2) and showed
moderate cytotoxicity against human colonic carci-
noma HCT-116 cells.
Taking into account broad spectrum of biological
activity of arenamides and keen interest of our research
team in total and formal syntheses of natural com-
pounds from hydroxy esters [14–31], a novel proce-
dure has been developed for the preparation of
protected (3S,4S)-3-hydroxy-4-methyldecanoic acid 2
which is the most complex molecular fragment of
macrolides 1a–1c (Scheme 1). The starting compound
for the synthesis of 2 was (7S)-7-(3-bromoprop-1-en-
2-yl)-5,5-dimethyl-4,6-dioxaspiro[2.5]octane (4). It
was obtained in enantiomerically pure form according
to the previously described scheme [32, 33] from
diethyl (S)-malate in six preparative steps using the
Gly
O
Me
H
N
25
28
26
29
R'
NH
20
O
O
O
O
Me
Val
Me
1
19
O
2
R
HN
H
11
10
N
H
N
13
Phe/Met
Leu
Me
Ala
Me
1a–1c
O
Me
R = Ph, R′ = C6H13 (a), Bu (b); R = MeSCH2, R′ = C6H13 (c).
* Stereodiad (propionate) block is a three-carbon fragment with
vicinal hydroxy and methyl substituents in polyketide molecules.
582

NEW SYNTHESIS OF syn-STEREODIAD BUILDING BLOCK FOR POLYKETIDES.
583
Scheme 1.
CH2
CH2
Me
6 steps [32]
EtOCO
COOMe
COOEt
1a, 1c
C6H13
COOH
OSiMe2Bu-t
O
O
Br
O
O
OH
Me
Me
Me
Me
2
3
4
Diethyl (S)-malate
Scheme 2.
Me
Me
CHO
O
Me
[30]
[31]
N
COOEt
4
O
S
OSiMe2Bu-t
5
6
Kulinkovich reaction [34–40] and cationic cyclo-
propyl–allyl isomerization of the corresponding cyclo-
propyl methanesulfonate [41–43]. Compound 4 was
used previously as a chiral precursor of key building
blocks for the synthesis of epothilones 5 and crypto-
phycins 6 which exhibit pronounced Taxol-like activity
(Scheme 2) [30, 31].
to result from the Williamson reaction of allyl alcohol
9 with initial allyl bromide 4. Alcohol 9 obtained in
two steps through acetate 8 was converted into unsatu-
rated ester 3 in a one-pot procedure. The acetonide
protection was removed by methanolysis in the pres-
ence of pyridinium p-toluenesulfonate, the hydroxy-
cyclopropane fragment was cleaved with (diacetoxy-
λ3-iodanyl)benzene according to Kirihara [45, 46], and
the resulting dihydroxy ester was protected again by
treatment with 2,2-dimetoxypropane in acetone. The
reduction of the exocyclic double bond in 3 with
hydrogen (1 atm) over a catalytic amount of Pd/C,
Pd(OH)2/C, or platinum black in methanol or ethyl
acetate led to the formation of complex mixtures of
difficultly identifiable products. It is known that cata-
lysts based on Group 10 metals (especially palladium
catalysts) show a high efficiency in the hydrogenolysis
Following the developed scheme, direct nucleo-
philic substitution of the bromine atom in 4 by hy-
droxy group was attempted by heating a solution of 4
and KOH in boiling ethanol (Scheme 3). The major
product was a colorless oily substance whose chro-
1
matographic mobility and H NMR spectrum were
fairly similar to those of initial bromide 4, but it
showed a negative Beilstein’s halogen test [44].
On the basis of elemental analysis, the product was
assigned the structure of diallyl ether 7 which is likely
Scheme 3.
(1) MeOH, PPTS
(2) PhI(OAc)2
(3) Me2C(OMe)2
Me2CO
CH2
CH2
Me
NiCl2·6H2O
NaBH4, MeOH
KOAc, DMF
COOMe
COOMe
OR
O
O
O
O
O
O
Me
Me
Me
Me
Me
Me
3
10
KOH, MeOH
8
9
4
R = Ac
R = H
CH2
CH2
O
KOH, EtOH
O
O
O
O
Me
Me
Me
Me
7
PPTS is pyridinium p-toluenesulfonate.
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 4 2015

SHKLYARUCK
was 16.7:1:2.53. The relative configuration of the
584
Scheme 4.
Me
chiral centers in syn-10 was determined by the
1D-gNOESY technique, as well as by comparing the
4-H/5-H coupling constant with that found for anti-10
(Scheme 4); the diastereoisomeric excess (de) was
89% in favor of syn-10 (according to the H NMR
data). The diastereoisomers are chromatographically
indistinguishable (retention time 47.75 min for both).
Me
COOMe
O
Me
H
O
O
O
H
1
MeOCO
Me
Me
syn-10
H
Me
NOE
Spin–spin coupling
Methyl ester 10 was reduced with lithium tetra-
hydridoaluminate in THF to obtain primary alcohol 11
(tR = 70.23 min) and its anti-diastereoisomer (tR =
68.87 min) at a ratio of 18.5:1 (GC/MS). The primary
hydroxy group in 11 was protected by benzylation, the
acetonide protection was removed, and the 1,3-diol
fragment of 13 was selectively protected via succes-
sive transformation into p-toluenesulfonate 14 and tert-
butyl(dimethyl)silyl ether 15. The Grignard–Schlosser
sp3–sp3 cross-coupling [61–63] of 15 with C5H11MgBr
smoothly afforded protected diol 16 (Scheme 5).
of R–O bonds** in allyl, propargyl, and benzyl sub-
strates and that rhodium- and ruthenium-based cata-
lysts [47, 48] and palladium deactivated with triethyl-
amine [49–54] are almost inefficient in this respect.
The best result in the reduction of 3 was obtained using
accessible NiCl2–NaBH4–MeOH system [55–59] at
0°C. Lowering the temperature to –10°C led to reduced
conversion of the initial compound, whereas decreased
diastereoselectivity was observed at room temperature.
1
The H NMR spectrum of the hydrogenation product
mixture contained upfield doublets from methyl
protons of syn isomer 10 (δ 1.06 ppm) and minor anti
isomer 10 [31] (δ 0.75 ppm) and doublets from protons
of the two diastereotopic methyl groups (δ 0.91 and
0.94 ppm [60]) in methyl (S)-3-hydroxy-4-methyl-
pentanoate resulting from hydrogenolysis of the allylic
moiety. The molar ratio of the hydrogenation products
The key building block for arenamides A and C,
carboxylic acid 2, was obtained by removal of the
benzyl protecting group from 16 and subsequent
oxidation of the primary hydroxy group in 17 accord-
ing to the procedure described in [64]. The yield of
target product 2 was 6.2% in 18 preparative steps, the
diastereoisomeric excess being 89%.
Scheme 5.
Me
Me
Me
NaH, BzlBr
Bu4NI, THF
LiAlH4, THF
MeOH, PPTS
10
O
O
OH
O
O
OBzl
OH
OH
OBzl
Me
Me
Me
Me
12
11
13
t-Bu(Me)2SiOSO2CF3
2,6-dimethylpyridine
CH2Cl2
Me
Me
TsCl, Et3N, DMAP
CH2Cl2
OBzl
OTs OH
OBzl
OTs OSiMe2Bu-t
14
15
Me
Me
C5H11MgBr, CuBr·Me2S
Et2O–THF
PhI(OAc)2, TEMPO
MeCN–H2O
H2, Pd/C, EtOAc
OBzl
OH
2
C6H13
C6H13
OSiMe2Bu-t
OSiMe2Bu-t
17
16
** The ability of substrates ROX to undergo hydrogenolysis of the
R–O bond depends on the metal nature in the catalyst (Pd >
Pt >> Ni > Rh ≈ Ru). It decreases with rise in hydrogen pres-
sure and decrease of temperature, solvent polarity, and acceptor
properties of the X group.
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NEW SYNTHESIS OF syn-STEREODIAD BUILDING BLOCK FOR POLYKETIDES.
585
EXPERIMENTAL
21.16 (2C, CH3), 29.87 (2C, CH3), 36.75 (2C, CH2),
53.67 (2C), 68.94 (2CH), 70.40 (2C, CH2), 100.27 (2C),
112.77 (2C, CH2=), 145.72 (2C). Found, %: C 69.62;
H 9.07. C22H34O5. Calculated, %: C 69.81; H 9.05.
Commercial initial reactants were used without ad-
ditional purification. The solvents were dried accord-
ing to standard procedures and distilled prior to use.
Sorbfil plates (Krasnodar, Russia) were used for thin-
layer chromatography; the chromatograms were devel-
oped by treatment with a 3% solution of phospho-
molybdic acid in ethanol, followed by heating. The
1H and 13C NMR spectra were recorded on a Bruker
AC-400 spectrometer at 400 and 100.6 MHz, respec-
tively, using CDCl3 as solvent and reference (CHCl3,
δ 7.26 ppm; CDCl3, δC 77.0 ppm); 1D-gNOESY and
1D-gTOCSY experiments were performed using the
same instrument. The IR spectra were taken on
a Bruker Vertex 70 spectrometer. Pure compounds
were isolated by column chromatography on Merck 60
silica gel (70–230 mesh) or flash chromatography
(silica gel 60, 230–240 mesh). Gas chromatographic–
mass spectrometric analysis was performed on
a Hewlett Packard 5890/5972 GC/MS instrument
(electron impact, 70 eV, carrier gas helium, HP
INNOWax column, 50 m×0.20 mm). The melting
points were determined on an Apotec® apparatus. The
elemental analyses were performed by the semi micro
method.
(7S)-2-(5,5-Dimethyl-4,6-dioxaspiro[2.5]octan-
7-yl)prop-2-en-1-yl acetate (8). Fused potassium
acetate, 7.082 g (72.3 mmol), was added under argon
to a solution of 6.303 g (24.1 mmol) of bromide 4 in
53 mL of anhydrous DMF, and the mixture was stirred
for 90 min in a silicone bath heated to 70°C. When the
reaction was complete (TLC), the reaction flask was
cooled to room temperature and placed into an ice
bath, and 120 mL of water and 50 mL of diethyl ether
were added to the mixture. The organic phase was
separated, the aqueous phase was extracted with
diethyl ether (3×50 mL), the extracts were combined
with the organic phase, washed with brine, and dried
over Na2SO4. The drying agent was filtered off, the
filtrate was evaporated, and the residue was purified by
silica gel chromatography (gradient elution with petro-
leum ether–ethyl acetate, 20:1 to 5:1). Yield 4.811 g
(83%). IR spectrum (film), ν, cm–1: 3090, 1744, 1656.
1H NMR spectrum, δ, ppm: 0.38–0.44 m, 0.59–0.65 m,
0.72–0.78 m, and 0.82–0.88 m (1H each, CH2CH2);
1.08 d.d (1H, CCH2CH, J = 13.1, 2.6 Hz), 1.38 s and
1.54 s [3H each, C(CH3)2], 2.08 s (3H, CH3CO),
2.24 d.d (1H, CCH2CH, J1 = 13.1, 13.1 Hz), 4.57–
4.62 m (1H, CHO), 4.62–4.65 m (2H, CH2O), 5.19–
5.21 m and 5.25–5.27 m (1H each, CH2=). 13C NMR
spectrum, δC, ppm: 9.80 (CH2), 14.35 (CH2), 20.79
(CH3), 20.96 (CH3), 29.69 (CH3), 36.30 (CH2), 53.48
(C), 63.95 (CH2), 68.91 (CH), 100.21, 113.42 (CH2=),
143.74, 170.40. Found, %: C 64.82; H 8.37. C13H20O4.
Calculated, %: C 64.98; H 8.39.
(7S,7′S)-7,7′-(Oxydiprop-1-ene-3,2-diyl)bis-
(5,5-dimethyl-4,6-dioxaspiro[2.5]octane) (7). A solu-
tion of 2.361 g (9 mmol) of allyl bromide 4 and
1.010 g (18 mmol) of potassium hydroxide in 20 mL of
96% ethanol was heated for 3 h under reflux in
an argon atmosphere. The mixture was cooled to 20°C,
the solvent was removed under reduced pressure, and
20 mL of water and 20 mL of diethyl ether were added
to the residue. The organic phase was separated, and
the aqueous phase was extracted with diethyl ether
(3×10 mL). The extracts were combined with the
organic phase, washed with brine, and dried over
Na2SO4. The drying agent was filtered off, the filtrate
was evaporated, and the residue was purified by silica
gel chromatography (gradient elution with petroleum
ether to petroleum ether–ethyl acetate, 20:1). Yield
(7S)-2-(5,5-Dimethyl-4,6-dioxaspiro[2.5]octan-7-
yl)prop-2-en-1-ol (9). Powdered potassium hydroxide,
2.00 g (35.7 mmol), was added under stirring in
an argon atmosphere to a solution of 4.279 g
(17.8 mmol) of acetate 8 in 70 mL of methanol, and
the mixture was stirred for 2 h at room temperature.
The solvent was removed under reduced pressure, and
50 mL of water and 50 mL of methylene chloride were
added to the residue. The organic phase was separated,
and the aqueous phase was extracted with methylene
chloride (3×30 mL). The extracts were combined with
the organic phase, washed with brine, and dried over
Na2SO4. The drying agent was filtered off, the filtrate
was evaporated, and the residue was purified by silica
gel flash chromatography (gradient elution with petro-
leum ether–ethyl acetate, 10:1 to 2:1). Yield 3.354 g
(95%). IR spectrum (film), ν, cm–1: 3413, 3087, 1656.
1
1.204 g (70%). H NMR spectrum, δ, ppm: 0.39 d.d.d
(2H, CH2CH2, J = 10.2, 6.4, 5.6 Hz), 0.59–0.65 m (2H,
CH2CH2), 0.75 d.d.d (2H, CH2CH2, J = 10.8, 6.4,
5.6 Hz), 0.81–0.89 m (2H, CH2CH2), 1.11 d.d (2H,
CCH2CH, J = 13.1, 2.6 Hz), 1.40 s and 1.55 s [6H
each, C(CH3)2], 2.17–2.25 m (2H, CCH2CH), 4.00–
4.04 m (4H, CH2O), 4.58–4.63 m (2H, CHO), 5.17–
5.20 m and 5.24–5.27 m (2H each, CH2=). 13C NMR
spectrum, δC, ppm: 9.90 (2C, CH2), 14.51 (2C, CH2),
RUSSIAN JOURNAL OF ORGANIC CHEMISTRY Vol. 51 No. 4 2015

SHKLYARUCK
586
1H NMR spectrum, δ, ppm: 0.38–0.44 m, 0.61–0.67 m,
0.72–0.78 m, and 0.84–0.89 m (1H each, CH2CH2);
1.05 d.d (1H, CCH2CH, J = 13.1, 2.8 Hz), 1.40 s
and 1.57 s [3H each, C(CH3)2], 2.28–2.38 m (2H,
CCH2CH, OH), 4.10–4.17 m and 4.23–4.30 m (1H
each, CH2O), 4.70–4.75 m (1H, CHO), 5.12–5.17 m
itate was filtered off on a Schott filter, the filtrate was
concentrated under reduced pressure, and the residue
was purified by silica gel chromatography (gradient
elution with petroleum ether to petroleum ether–ethyl
acetate, 15:1). Yield 1.560 g (84%), de = 89%, tR =
47.75 min. IR spectrum (CCl4): ν 1743 cm–1. 1H NMR
spectrum, δ, ppm: 1.06 d (3H, CH3CH, J = 6.9 Hz),
1.36 s and 1.44 s [3H each, C(CH3)2], 1.50–1.58 m
(1H, CHCH3), 2.34 d.d (1H, CH2CO, J = 15.6,
5.6 Hz), 2.50 d.d (1H, CH2CO, J = 15.6, 7.9 Hz),
3.57 d.d (1H, CH2O, J = 11.5, 1.5 Hz), 3.67 s (3H,
CH3O), 4.13 d.d (1H, CH2O, J = 11.5, 2.6 Hz),
4.45 d.d.d (1H, CHO, J = 7.9, 5.6, 2.6 Hz). 13C NMR
spectrum, δC, ppm: 10.69 (CH3), 18.90 (CH3), 29.47
(CH3), 31.20 (CH), 38.05 (CH2), 51.59 (OCH3), 66.52
(CH2), 68.17 (CH), 98.86, 171.60. Found, %: C 59.44;
H 8.95. C10H18O4. Calculated, %: C 59.39; H 8.97.
13
(2H, CH2=). C NMR spectrum, δC, ppm: 9.86 (CH2),
14.50 (CH2), 21.09 (CH3), 29.87 (CH3), 36.48 (CH2),
53.57, 64.10 (CH2), 70.80 (CH), 100.37, 112.78
(CH2=), 147.89. Found, %: C 66.51; H 9.17. C11H18O3.
Calculated, %: C 66.64; H 9.15.
Methyl 2-[(4S)-2,2-dimethyl-5-methylidene-
1,3-dioxan-4-yl]acetate (3). A solution of 3.125 g
(15.8 mmol) of alcohol 9 and 0.397 g (1.58 mmol) of
pyridinium p-toluenesulfonate in 110 mL of anhydrous
methanol was heated under argon to 40°C until the
initial compound disappeared (TLC). The mixture was
cooled to room temperature, 5.342 g (16.6 mmol) of
PhI(OAc)2 [65] was added in portions under stirring
over a period of 5 min (vigorous evolution of ethyl-
ene!), and the mixture was stirred for 10 min more.
The solvent was removed under reduced pressure, the
residue was kept for 10 min in an oil-pump vacuum
and dissolved in 100 mL of anhydrous acetone, and
4.0 mL (32.6 mmol) of 2,2-dimethoxypropane was
added. The mixture was stirred for 2 h at room
temperature, the solvent was removed under reduced
pressure, and the residue was purified by silica gel
chromatography (gradient elution with petroleum ether
to petroleum ether–ethyl acetate, 10:1). Yield 2.241 g
(71%). IR spectrum (CCl4), ν, cm–1: 3088, 1746, 1658.
1H NMR spectrum, δ, ppm: 1.36 s and 1.48 s [3H each,
C(CH3)2], 2.59 d.d (1H, CH2CO, J = 15.6, 8.2 Hz),
2.77 d.d (1H, CH2CO, J = 15.6, 4.6 Hz), 3.71 s (3H,
CH3O), 4.21–4.27 m and 4.30–4.36 m (1H each,
CH2O), 4.77–4.79 m and (1H, CH2=), 4.81–4.88 m
(2H, CH2=, CHO). 13C NMR spectrum, δC, ppm: 21.43
(CH3), 27.02 (CH3), 37.76 (CH2), 51.72 (OCH3), 63.99
(CH2), 67.57 (CH), 99.79, 106.56 (CH2=), 144.68,
171.38. Found, %: C 59.89; H 8.03. C10H16O4. Calcu-
lated, %: C 59.98; H 8.05.
2-[(4S,5S)-2,2,5-Trimethyl-1,3-dioxan-4-yl]-
ethanol (11). A solution of 1.455 g (7.20 mmol) of
ester 10 in 15 mL of anhydrous THF was added drop-
wise under stirring to a suspension of 0.274 g
(7.20 mmol) of LiAlH4 in 20 mL of anhydrous THF,
cooled to –10°C in an ice–salt bath. The mixture was
allowed to warm up to room temperature and stirred
for 1 h. When the reaction was complete, the mixture
was cooled to –10°C, hydrated sodium sulfate slurry
was added in small portions until hydrogen no longer
evolved, and the mixture was allowed to warm up to
room temperature and stirred for 30 min until forma-
tion of a loose white solid covered by transparent
liquid. The precipitate was filtered off through a Schott
filter and washed with THF (2×30 mL), the filtrate
was evaporated, and the residue was purified by silica
gel flash chromatography (gradient elution with petro-
leum ether–ethyl acetate, 10:1 to 2:1). Yield 1.241 g
(99%), tR = 70.23 (syn-11), 68.87 min (anti-11). IR
1
spectrum (CCl4), ν, cm–1: 3640, 3541. H NMR spec-
trum, δ, ppm: 1.10 d (3H, CH3CH, J = 7.1 Hz), 1.39 s
[3H, C(CH3)2], 1.42–1.52 m [5H, C(CH3)2, CH2CH2O],
1.80–1.91 m (1H, CHCH3), 2.34 br.s (1H, OH),
3.59 d.d (1H, CH2CHCH3, J = 11.5, 1.5 Hz), 3.71–
3.81 m (2H, CH2CH2O), 4.13 d.d (1H, CH2CHCH3,
J = 11.5, 2.8 Hz), 4.22 d.d.d (1H, CHO, J = 10.0, 2.8,
2.6 Hz). 13C NMR spectrum, δC, ppm: 10.95 (CH3),
19.22 (CH3), 29.69 (CH3), 32.14 (CH), 35.13 (CH2),
61.56 (CH2), 66.82 (CH2), 71.82 (CH), 98.66. Found,
%: C 61.93; H 10.42. C9H18O3. Calculated, %:
C 62.04; H 10.41.
Methyl 2-[(4S,5S)-2,2,5-trimethyl-1,3-dioxan-
4-yl]acetate (10). A solution of 1.839 g (9.2 mmol)
of ester 3 in 35 mL of methanol was cooled to 0°C,
a solution of 0.55 g (2.3 mmol) of NiCl2 ·6 H2O in
15 mL of methanol was added in one portion under
vigorous stirring, and 0.7 g (18.4 mmol) of NaBH4 was
then added in portions over a period of 15 min
(vigorous evolution of hydrogen). The resulting black
suspension containing nickel boride was stirred until
the initial compound disappeared (TLC), the precip-
(4S,5S)-4-[2-(Benzyloxy)ethyl]-2,2,5-trimethyl-
1,3-dioxane (12) [66]. A solution of 1.133 g
(6.51 mmol) of alcohol 11 in 60 mL of anhydrous THF
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NEW SYNTHESIS OF syn-STEREODIAD BUILDING BLOCK FOR POLYKETIDES.
587
was cooled to 0°C, and 0.52 g (13 mmol) of sodium
hydride (60% suspension in mineral oil) was added in
portions under argon. When vigorous foaming ceased,
the cooling bath was removed, and the mixture was
stirred for 30 min at room temperature. Tetrabutyl-
ammonium iodide, 0.24 g (0.65 mmol), was added in
one portion to the resulting suspension of sodium
alkoxide, and 1.55 mL (13 mmol) of benzyl bromide
was then added. The mixture was stirred for 12 h at
room temperature and cooled to 0°C, and 30 mL of
a saturated aqueous solution of sodium hydrogen
carbonate was added (vigorous foaming!). The organic
phase was separated, the aqueous phase was extracted
with diethyl ether Et2O (3×10 mL), and the extracts
were combined with the aqueous phase, washed with
brine, and dried over Na2SO4. The drying agent was
filtered off, the filtrate was evaporated, and the residue
was purified by silica gel chromatography (gradient
elution with petroleum ether to petroleum ether–ethyl
acetate, 40:1). Yield 1.376 g (80%). IR spectrum
(film), ν, cm–1: 3063, 1496, 1379, 1367, 1111, 737,
a solution of 0.524 g (2.75 mmol) of p-toluenesulfonyl
chloride in 5 mL of methylene chloride was added
dropwise under stirring. The mixture was stirred for
1 h at –10°C, allowed to warm up to room tempera-
ture, stirred for 12 h, and treated with 10 mL of water.
The organic phase was separated, the aqueous phase
was extracted with methylene chloride (2×5 mL), and
the extracts were combined with the organic phase,
washed with brine, and dried over Na2SO4. The drying
agent was filtered off, the filtrate was evaporated, and
the residue was purified by silica gel chromatography
(gradient elution with petroleum ether–ethyl acetate,
15:1 to 4:1). Yield 0.676 g (78%). IR spectrum (film),
ν, cm–1: 3501, 3065, 1359, 1598, 1177, 966, 668, 555.
1H NMR spectrum, δ, ppm: 0.88 d (3H, CH3CH, J =
6.9 Hz), 1.51–1.61 m (1H, CH2CH2O), 1.76–1.95 m
(2H, CH2CH2O, CHCH3), 2.43 s (3H, C6H4CH3),
2.95 s (1H, OH), 3.58–3.74 m (2H, CH2CH2O,
CHOH), 3.86–3.94 m (2H, CH2CH2O, CH2CHCH3),
4.07 d.d (1H, CH2CHCH3, J = 9.2, 7.4 Hz), 4.46–
4.55 m (2H, C6H5CH2), 7.25–7.38 m (7H, Harom),
7.75–7.82 m (2H, C6H4). 13C NMR spectrum, δC, ppm:
10.13 (CH3), 21.57 (CH3), 33.54 (CH2), 38.30 (CH),
69.55 (CH2), 70.64 (CH), 72.56 (CH2), 73.36 (CH2),
127.63 (2C, CH), 127.77 (CH), 127.85 (2C, CH),
128.44 (2C, CH), 129.77 (2C, CH), 132.89, 137.65,
144.64. Found, %: C 63.59; H 6.94. C20H26O5S. Calcu-
lated, %: C 63.47; H 6.92.
1
698. H NMR spectrum, δ, ppm: 1.06 d (3H, CH3CH,
J = 6.9 Hz), 1.38 s [3H, C(CH3)2], 1.40–1.46 m [4H,
C(CH3)2, CH2CH2O], 1.58–1.67 m (1H, CH2CH2O),
1.70–1.81 m (1H, CHCH3), 3.47–3.60 m (3H,
CH2CH2O, CH2CHCH3), 4.11 d.d (1H, CH2CHCH3,
J = 11.5, 2.8 Hz), 4.17 d.d.d (1H, CHO, J = 8.8, 4.1,
2.8 Hz), 4.46–4.54 m (2H, C6H5CH2), 7.31–7.37 m
(5H, C6H5). 13C NMR spectrum, δC, ppm: 10.67 (CH3),
19.12 (CH3), 29.68 (CH3), 31.87 (CH), 35.35 (CH2),
66.55 (CH2), 66.91 (CH2), 68.13 (CH), 73.07 (CH2),
98.60, 127.55 (CH), 127.65 (2C, CH), 128.35 (2C,
CH), 138.48. Found, %: C 72.77; H 9.13. C16H24O3.
Calculated, %: C 72.69; H 9.15.
(2S,3S)-5-(Benzyloxy)-3-[tert-butyl(dimethyl)-
silyloxy]-2-methylpentyl 4-methylbenzenesulfonate
(15). A solution of 0.180 g (0.48 mmol) of alcohol 14
and 0.25 g (2.33 mmol) of 2,6-dimethylpyridine in
2 mL of anhydrous methylene chloride was cooled to
0°C, and 0.19 g (0.72 mmol) of tert-butyl(dimethyl)-
silyl trifluoromethanesulfonate was added dropwise
under stirring. The mixture was stirred for 30 min at
0°C, diluted with 10 mL of diethyl ether, washed with
a saturated aqueous solution of NaHCO3, water, and
brine, and dried over Na2SO4. The drying agent was
filtered off, the filtrate was evaporated, and the residue
was purified by silica gel chromatography (gradient
elution with petroleum ether–ethyl acetate, 10:1 to
3 :1). Yield 0.230 g (98%). IR spectrum (CCl4), ν,
cm–1: 3032, 1600, 1373, 1189, 1179, 1099, 945.
1H NMR spectrum, δ, ppm: –0.05 s and –0.01 s (3H
each, SiCH3), 0.79 s (9H, t-Bu), 0.85 d (3H, CH3CH,
J = 6.9 Hz), 1.55–1.66 m and 1.69–1.78 m (1H each,
CH2CH2O), 1.87–1.97 m (1H, CHCH3), 2.44 s (3H,
C6H4CH3), 3.39–3.45 m (2H, CH2CH2O, CHOSi),
3.81–3.88 m (2H, CH2CH2O, CH2CHCH3), 4.03 d.d
(1H, CH2CHCH3, J = 9.0, 5.9 Hz), 4.40–4.50 m (2H,
(2S,3S)-5-(Benzyloxy)-2-methylpentane-1,3-diol
(13). A solution of 0.967 g (3.66 mmol) of acetonide
12 and 0.1 g (0.40 mmol) of PPTS in 25 mL of
methanol was heated for 2 h under reflux (TLC). The
mixture was cooled to room temperature and evaporat-
ed under reduced pressure, and the residue was
purified by silica gel chromatography (gradient elution
with petroleum ether–ethyl acetate, 4:1 to 1:1). Yield
0.682 g (83%), colorless crystals, mp 43.4°C. The
spectral parameters of the product were identical to
those reported in [11].
(2S,3S)-5-(Benzyloxy)-3-hydroxy-2-methylpentyl
4-methylbenzenesulfonate (14). A solution of 0.512 g
(2.29 mmol) of diol 13, 0.531 g (5.26 mmol) of
triethylamine, and 14 mg (0.115 mmol) of 4-(dimethyl-
amino)pyridine in 15 mL of anhydrous methylene
chloride was cooled to –10°C (ice–salt bath), and
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SHKLYARUCK
588
C6H5CH2), 7.25–7.37 m (7H, Harom), 7.75–7.80 m (2H,
C6H4). 13C NMR spectrum, δC, ppm: –4.83 (CH3),
–4.55 (CH3), 11.09 (CH3), 17.91, 21.55 (CH3), 25.71
(3C, CH3), 33.60 (CH2), 37.00 (CH), 66.79 (CH2), 69.37
(CH), 72.57 (CH2), 72.93 (CH2), 127.52 (CH), 127.55
(2C, CH), 127.89 (2C, CH), 128.32 (2C, CH), 129.74
(2C, CH), 132.98, 138.28, 144.57. Found, %: C 63.50;
H 8.16. C26H40O5SSi. Calculated, %: C 63.38; H 8.18.
(3S,4S)-3-[tert-Butyl(dimethyl)silyloxy]-
4-methyldecan-1-ol (17). Benzyl ether 16, 0.082 g
(0.21 mmol), was dissolved in 5 mL of ethyl acetate,
0.02 g of 10% Pd/C was added, and the resulting sus-
pension was stirred for 4 h in a hydrogen atmosphere
(1 atm). The catalyst was filtered off through a Schott
filter, the filtrate was evaporated under reduced pres-
sure, and the residue was purified by silica gel chroma-
tography (petroleum ether–ethyl acetate, 20:1). Yield
0.061 g (97%). The spectral parameters of 17 coin-
cided with those given in [13].
[(3S,4S)-1-(Benzyloxy)-4-methyldec-3-yloxy]-
(tert-butyl)dimethylsilane (16). A solution of
Grignard compound prepared from 0.018 g
(0.75 mmol) of magnesium and 0.112 g (0.74 mmol)
of 1-bromopentane in 0.8 mL of anhydrous THF was
added under stirring in an argon atmosphere to a sus-
pension of 5.6 mg (0.0272 mmol) of CuBr·Me2S
[67, 68] in 0.5 mL of anhydrous THF, cooled to –78°C.
The mixture was stirred for 20 min at –78°C, a solu-
tion of 0.168 g (0.34 mmol) of compound 15 in 0.5 mL
of anhydrous diethyl ether was added dropwise, and
the mixture was allowed to warm up to room tempera-
ture over a period of 2 h and then stirred for 12 h and
left overnight. The mixture was heated for 1 h under
reflux, cooled to room temperature, diluted with 10 mL
of diethyl ether, and poured into a mixture of ice with
a saturated aqueous solution of ammonium chloride.
The organic phase was separated, and the aqueous
phase was extracted with diethyl ether (3×5 mL). The
extracts were combined with the organic phase,
washed in succession with saturated aqueous solutions
of NH4Cl, NaHCO3, and NaCl, and dried over MgSO4.
The drying agent was filtered off, the filtrate was
evaporated under reduced pressure, and the residue
was purified by silica gel chromatography (gradient
elution with petroleum ether to petroleum ether–ethyl
acetate, 40:1). Yield 0.098 g (73%). IR spectrum
(CCl4), ν, cm–1: 3032, 1559, 1472, 1462, 1260.
1H NMR spectrum, δ, ppm: –0.02 s and –0.07 s
(3H, SiCH3), 0.79–0.92 m [15H, t-Bu, (CH2)5CH3,
CH3CH], 0.96–1.07 m [1H, CH2CH2(CH2)3CH3],
1.13–1.38 m [8H, (CH2)5CH3], 1.44–1.54 m [2H,
CHCH3, CH2(CH2)4CH3], 1.62–1.79 m (2H,
CH2CH2O), 3.46–3.56 m (2H, CH2CH2O), 3.67–
3.74 m (1H, CHOSi), 4.44–4.55 m (2H, C6H5CH2),
7.25–7.39 m (5H, C6H5). 13C NMR spectrum, δC, ppm:
–4.52 (CH3), –4.38 (CH3), 14.09 (CH3), 14.85 (CH3),
18.11, 22.66 (CH2), 25.90 (3C, CH3), 27.71 (CH2),
29.65 (CH2), 31.73 (CH2), 31.89 (CH2), 33.09 (CH2),
38.49 (CH), 67.70 (CH2), 72.91 (CH2), 73.02 (CH),
127.44 (CH), 127.62 (2C, CH), 128.30 (2C, CH),
138.62. Found, %: C 73.25; H 11.32. C24H44O2Si. Cal-
culated, %: C 73.41; H 11.29.
(3S,4S)-3-[tert-Butyl(dimethyl)silyloxy]-
4-methyldecanoic acid (2). An emulsion of 0.048 g
(0.16 mmol) of compound 17 in a mixture of 0.2 mL of
acetonitrile and 0.2 mL of water was cooled to 0°C,
and 5 mg (0.032 mmol) of 2,2,6,6-tetramethylpiperi-
dine-1-oxyl and 0.113 g (0.35 mmol) of (diacetoxy-λ3-
iodanyl)benzene were added in succession under
argon. The mixture was stirred for 3 min at 0°C, the
cooling bath was removed, and the mixture was stirred
for 4 h at room temperature (TLC). The resulting
solution was treated with 0.4 mL of 10% aqueous
Na2S2O3, and the solvent was removed under reduced
pressure. The residue was diluted with ethyl acetate
(10 mL), the solution was washed with brine (2 mL),
and the organic phase was separated, dried over
MgSO4, and evaporated under reduced pressure. The
residue was purified by silica gel column chroma-
tography (petroleum ether–ethyl acetate, 2:1). Yield
0.049 g (98%). IR spectrum (CCl4), ν, cm–1: 2930,
1
1711. H NMR spectrum, δ, ppm: 0.05 s and 0.07 s
(3H each, SiCH3), 0.82–0.92 m [15H, t-Bu,
(CH2)5CH3, CH3CH], 0.96–1.07 m [1H, CH2CH2-
(CH2)3CH3], 1.16–1.38 m [8H, (CH2)5CH3], 1.46–
1.62 m [2H, CHCH3, CH2(CH2)4CH3], 2.45 d (2H,
CH2COOH, J = 5.9 Hz), 4.01–4.07 m (1H, CHOSi),
11.0 br.s (1H, COOH). 13C NMR spectrum, δC, ppm:
–4.79 (CH3), –4.64 (CH3), 14.05 (CH3), 14.85 (CH3),
18.00, 22.61 (CH2), 25.75 (3C, CH3), 27.45 (CH2),
29.52 (CH2), 31.61 (CH2), 31.80 (CH2), 38.65 (CH2),
38.80 (CH), 72.97 (CH2), 176.93 (C). Found, %:
C 64.69; H 11.43. C17H36O3Si. Calculated, %: C 64.50;
H 11.46.
This study was performed under financial support
by the Ministry of Education of Belarus Republic.
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