An expeditious route to the antipode of harzialactone a

Article abstract of DOI:10.1016/j.tetasy.2005.07.003

The antipode of the antitumor marine metabolite harzialactone A was synthesized from l-malic acid via a very efficient route in 40% overall yield involving only two chromatographic separations.

Full text of DOI:10.1016/j.tetasy.2005.07.003

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 16 (2005) 2649–2651
An expeditious route to the antipode of harzialactone A
Ya-Jun Jian,a,b Yikang Wu,b,* Liang Lib and Jun Lua
aDepartment of Chemistry, The Northwest University, XiÕan 710069, China
bState Key Laboratory of Bio-organic and Natural Products Chemistry, Shanghai Institute of Organic Chemistry,
Chinese Academy of Sciences, 354 Fenglin Road, Shanghai 200032, China
Received 7 June 2005; accepted 1 July 2005
Abstract—The antipode of the antitumor marine metabolite harzialactone A was synthesized from L-malic acid via a very efficient
route in 40% overall yield involving only two chromatographic separations.
ꢀ 2005 Elsevier Ltd. All rights reserved.
1. Introduction
tions were executed. Examples of making C–C bond
selectively at the free carboxylic end of 2 are scant.3 This
approach needs further exploration to seek more appli-
cations for 2.
Harzialactone A (+)-1 is an antitumor marine metabo-
lite isolated from a strain of Trichoderma harianium
OUPS-N 115 made by Numata and co-workers.1 In
connection with establishing absolute configuration,
Mereyala et al.2 synthesized this compound from D-glu-
cose (seven steps, 15% overall yield) and D-xylose (seven
or eight steps, 24% overall yield). In these, the undesired
extra oxygen atoms in the sugars were removed by
radical-mediated reactions involving Bu3SnH with the
oxidation of the lactol to lactone being achieved with
Ag2CO3. Herein, we report an expeditious route to
(ꢀ)-harzialactone A, the antipode of the natural (+)-1,
starting from L-malic acid. This has also been synthe-
sized by Mereyala et al.2 from D-glucose in <17% overall
yield over nine steps.
The starting material 2 was very conveniently derived
from L-malic acid in 100% yield following the procedure
of Larcheveque4 (AcCl/40 ꢁC/2 h, then MeOH/rt/over-
night) without any need for chromatographic purifica-
tion. Compound
2
was then converted3 to the
corresponding acid chloride by treatment with SOCl2
at 42 ꢁC and the crude product used directly in the next
step after removal of excess SOCl2.
In order to keep the two carbonyl groups in 2 intact, the
introduction of a benzyl group was planned. We tried
several reagents including PhCH2Cu(CN)ZnBr,5
PhCH2SbBu4,6 PhCH2MgBr/Fe(acac)3,7 and PhCH2-
MgBr/CuI8 that were known to react selectively with
acid halides but not with esters. However, none of these
worked well with our substrate. Under PhCH2-
Cu(CN)ZnBr conditions, the desired product 3 could
be isolated albeit in 38% yield only. Other conditions
mentioned above led to a very complicated product mix-
ture. The problem was finally overcome by using
PhCH2ZnBr/PdCl2(PPh3)2.9 In this case, ketone 3 was
obtained in 59% isolated yield (Scheme 1).
2. Results and discussion
Our plan was very straightforward, making use of the
readily accessible building block 2 by first converting it
into the corresponding acid halide and then attaching
a benzyl group to it. The stereogenic center at the benz-
ylic position was planned to be established through a
stereocontrolled reduction induced by the chiral OH in
the malic residue. It should be noted that although the
malic acid residue has been broadly used as a chiral pool
in the asymmetric synthesis, in most cases it was reduced
either partially or completely before other transforma-
The acetyl protecting group was readily removed with
a catalytic amount of p-TsOH in MeOH, giving 4 in
93% yield. The same alcohol could also be obtained
in comparable yields (55% yield from malic acid)
even from crude 3. The ketone carbonyl group was
then reduced using the procedure of Prasad et al.10
*
Corresponding author. E-mail: yikangwu@mail.sioc.ac.cn
0957-4166/$ - see front matter ꢀ 2005 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2005.07.003

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Y.-J. Jian et al. / Tetrahedron: Asymmetry 16 (2005) 2649–2651
O
O
a
CO2Me
OAc
CO2Me
b
CO Me
c
2
HO2C
Ph
Ph
Ph
O
OAc
O
OH
OH
(-)-1
4
2
3
Scheme 1. Reagents and conditions: (a) (i) SOCl2/42 ꢁC/3 h, (ii) 2.5 equiv BnZnBr/0.1 equiv PdCl2(PPh3)2/THF/rt/overnight, 59% from 2; (b)
p-TsOH/MeOH/rt/overnight/93%; (c) (i) Et2BOMe/THF–MeOH (4:1)/NaBH4/ꢀ78 ꢁC/5 h, (ii) p-TsOH/CH2Cl2/rt/overnight, 73% from 4.
(NaBH4/Et2BOMe/THF–MeOH/ꢀ78 ꢁC) to yield an
intermediate diol. As the syn- and anti-diols generated
at this step were inseparable on TLC, the crude product
was directly cyclized by treatment with a catalytic
amount of p-TsOH in CH2Cl2. (ꢀ)-Harzialactone A
and the isomer derived from the anti-diol could be sep-
arated to obtain (ꢀ)-1 in 73% isolated yield. From the
1H NMR analysis (the integral ratio of the signal for
the BnCH-O at d 4.92 and 4.61, respectively) of the
crude mixture, the trans/cis lactone ratio (and thus the
syn/anti diol ratio) was estimated to be 20:1.
halide4 [prepared from11 2 (187 mg, 1.0 mmol)] and
PdCl2(PPh3)2 (71 mg, 0.1 mmol) in THF (1 mL) cooled
in a ice-water bath. After stirring at room temperature
overnight, the reaction mixture was diluted with water
(10 mL) and extracted with ether (3 · 10 mL). The
extract was dried over anhydrous Na2SO4 and concen-
trated on a rotary evaporator. The residue was purified
by column chromatography (silica gel, 5:4 n-hexane–
25
Et2O) to give 3 as a yellowish oil (153 mg, 59%): ½aꢁD
=
1
ꢀ19.3 (c 1.17, CHCl3); H NMR (300 MHz, CDCl3) d
7.39–7.29 (m, 3H), 7.23–7.18 (m, 2H), 5.47 (dd,
J = 4.0, 3.6 Hz, 1H), 3.74 (s, 2H), 3.72 (s, 3H), 2.98
(m, 2H), 2.07 (s, 3H); IR (film) 1748, 701 cmꢀ1; ESI-
MS 287.1 ([M+Na]+); ESI-HRMS calcd for
C14H16O5Na [M+Na]+: 287.08899. Found: 287.08897.
3. Conclusion
We have achieved an efficient synthesis of the antipode
of the antitumor marine metabolite harzialactone A
starting from L-malic acid. Only two chromatographic
separations were needed in the whole synthesis. The
overall yield (40%) was also significantly improved when
compared to those reported in the literature. As the sec-
ond stereogenic center at the benzylic position was con-
structed by substrate-induced stereoselective reduction,
the natural harzialactone A should also be accessible
by the same route by using D-malic acid as the starting
material.
4.2. Methyl (S)-2-hydroxy-4-oxo-5-phenylpentanoate 4
Compound 3 (130 mg, 0.5 mmol) was added to a solu-
tion of p-TsOH in MeOH (0.2 M, 3 mL) and the result-
ing mixture stirred at room temperature overnight. The
mixture was evaporated in vacuo and the residue puri-
fied by column chromatography (silica gel, 1:2 n-hex-
ane–Et2O) to give 4 as a yellowish oil (102 mg, 93 %):
25
½aꢁD = +3.3 (c 1.28, CHCl3); 1H NMR (300 MHz,
CDCl3) d 7.37–7.17 (m, 5H), 4.49 (m, 1H), 3.76 (s,
2H), 3.75 (s, 3H), 3.21 (br s, 1H, OH), 3.05–2.87 (m,
2H); IR (film) 3479, 1740, 1497, 701 cmꢀ1; ESI-MS
245.1 ([M+Na]+); ESI-HR MS calcd for C12H13O4Na
[M+Na]+: 2245.07843. Found: 245.07826.
4. Experimental
The 1H NMR spectra were recorded with a Varian Mer-
cury 300 (300 MHz) spectrometer. The FT-IR spectra
were scanned with a Nicolet Avatar 360 FT-IR. EI-
MS spectra were recorded with an HP 5989A mass spec-
trometer. The ESI-MS spectra were recorded with a PE
Mariner API-TOF or an Agilent Technologies LC/
MSD SL instrument. The ESI-HRMS spectra were
recorded with a APEX III (7.0 T) FTMS mass spectro-
meter. The melting points are uncorrected. The optical
4.3. (3S,5S)-(ꢀ)-5-Benzyl-3-hydroxy-dihydro-furan-
2-one (ꢀ)-1
To a cooled (ꢀ78 ꢁC) stirred solution of 4 (48 mg,
0.22 mmol) in anhydrous THF (1.6 mL) and MeOH
(0.4 mL) under a nitrogen atmosphere was injected a
solution of MeOBEt2 in THF (1 M, 0.24 mL,
0.24 mmol). Stirring was continued at ꢀ78 ꢁC for
15 min before NaBH4 (9 mg, 0.24 mmol) was added in
one portion. After stirring at ꢀ78 ꢁC for another 5 h,
the reaction was quenched (at ꢀ78 ꢁC) by the addition
of AcOH (0.2 mL). The mixture was poured into satu-
rated aqueous NaHCO3 (7 mL) and extracted with
EtOAc. The combined organic layers were washed with
brine, dried over Na2SO4, and concentrated in vacuo.
The residue was dissolved in MeOH (5 mL) and evapo-
rated to dryness with a rotary evaporator (repeated sev-
eral times). To the oily residue were added p-TsOH
(5 mg) and CH2Cl2 (2 mL) and the mixture stirred at
room temperature overnight. After aqueous workup,
the residue obtained was purified by column chromato-
graphy (silica gel, 2:1, n-hexane–EtOAc) to afford (ꢀ)-1
(31 mg, 73%) as colorless transparent needles: mp 73–
rotations were measured with
polarimeter.
a JASCO P-1030
4.1. Methyl (S)-2-acetoxy-4-oxo-5-phenylpentanoate 3
A mixture of zinc dust (163 mg, 2.5 mmol) and 1,2-di-
bromoethane (22 lL, 0.5 mmol) in anhydrous THF
(4 mL) was heated gently until boiling of the solvent
was observed. The suspension was stirred at room tem-
perature for a few minutes before being heated again (re-
peated three times). The mixture was then cooled to 0 ꢁC
and a solution of benzyl bromide (0.6 mL, 2.5 mmol) in
THF (2 mL) was added dropwise over 30 min. The
resulting mixture was stirred at room temperature for
1 h, and then added dropwise to a solution of the acid

Y.-J. Jian et al. / Tetrahedron: Asymmetry 16 (2005) 2649–2651
2651
25
75 ꢁC (lit.2b 71–74 ꢁC); ½aꢁD = ꢀ39.6 (c 0.32, CHCl3),
3. For the only precedents of this type in the literature we
could find so far, see: Shi, X.-X.; Wu, Q.-Q.; Lu, X.
Tetrahedron: Asymmetry 2002, 13, 2461–2464; Mori, S.;
Takechi, S.; Shimizu, S.; Kida, S.; Iwakura, H.; Hajima,
M. Tetrahedron Lett. 1999, 40, 1165–1168.
{lit.2b [a]D = ꢀ38 (c 0.3, CHCl3)}; 1H NMR
(300 MHz, CDCl3) d 7.37–7.18 (m, 5H), 4.92 (m, 1H),
4.00 (dt, J = 2.6, 7.8 Hz, 1H), 2.99 (d, J = 5.5 Hz, 2H),
2.81 (br s, 1H, OH), 2.42–2.23 (m, 2H).
4. Henrot, S.; Larcheveque, M.; Petit, Y. Synth. Commun.
1986, 16, 183–190.
5. Berk, S. C.; Knochel, P.; Ye, M. C. P. J. Org. Chem. 1988,
53, 5789–5791.
Acknowledgments
6. Zhang, L.-J.; Huang, Y.-Z.; Jiang, H.-X.; Duan-Mu, J.;
Liao, Y. J. Org. Chem. 1992, 57, 774–777.
7. Cardellicchio, C.; Fiandanese, V.; Marchese, G.; Ronzini,
L. Tetrahedron Lett. 1987, 28, 2053–2056.
8. Reppy, M. A.; Gray, D. H.; Pindzola, B. A.; Smithers,
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1999, 10, 4633–4637; (b) Tokuyama, H.; Yokoshima, S.;
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This work was supported by the National Natural
Science Foundation of China (20025207, 20272071,
20372075, and 20321202), the Chinese Academy of Sci-
ences (ÔKnowledge InnovationÕ project, KGCX2-SW-
209), and the Major State Basic Research Development
Program (G2000077502).
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1.0 mmol) in SOCl2 (0.9 mL) and heating the mixture to
42 ꢁC with stirring for 2.5 h, followed by removing the
excess SOCl2 under oil pump vacuum.
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