A concise synthesis of (+)-preussin

Article abstract of DOI:10.1016/S0040-4020(01)00292-7

A concise synthesis of (+)-preussin (1), an antifungal agent and a growth-inhibitor of fission yeast and human cancer cells, was accomplished employing a stereoselective aldol reaction between the zinc enolate of 2-undecanone and N-protected-L-phenylalaninal followed by reductive pyrrolidine formation as key steps.

Full text of DOI:10.1016/S0040-4020(01)00292-7

TETRAHEDRON
Pergamon
Tetrahedron 57 $2001) 4107±4110
A concise synthesis of ꢀ1)-preussin
Masayuki Okue,a Hidenori Watanabeb and Takeshi Kitaharab,p
aSNOW BRAND MILK PRODUCTS CO., LTD. Research Institute of Life Science, 519 Shimo-ishibashi, Ishibashi-machi,
Shimotsuga-gun, Tochigi 329-0512, Japan
bDepartment of Applied Biological Chemistry, Graduate School of Agricultural and Life Sciences, The University of Tokyo,
1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan
Received 5 February 2001; accepted 8March 2001
AbstractÐA concise synthesis of $1)-preussin $1), an antifungal agent and a growth-inhibitor of ®ssion yeast and human cancer cells, was
accomplished employing a stereoselective aldol reaction between the zinc enolate of 2-undecanone and N-protected-l-phenylalaninal
followed by reductive pyrrolidine formation as key steps. q 2001 Elsevier Science Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Preussin $L-657,398) $1), a naturally occurring pyrrolidine
alkaloid, has been isolated from fermentation broths of
Aspergillus ochraceus ACTT22947 and Preussia sp.1 and
exhibits antifungal and antibacterial activities.2 Following
the ®rst asymmetric synthesis of 1 by Pak et al. in 1991,3
several approaches to preussin itself and its stereoisomers
have been reported.4 In 1997, Yoshida, Horinouchi et al.
have rediscovered preussin as a selective inhibitor for cell
growth of the ®ssion yeast ts mutants defective on cdc2-
regulatory genes5 and more recently, its activities in apop-
tosis-induction and as a potent inhibitor of cyclin E kinase in
human tumor cells were reported by MuÈller et al.6 We were
interested in these bioactivities and investigated a concise
synthetic route to 1 and its analogs. Herein, we report a
short-step synthesis of preussin $1) with a stereoselective
aldol reaction to N-protected-l-phenylalaninal and reduc-
tive pyrrolidine formation as key steps $A1B in Scheme 1).
The substrate for the aldol reaction $2b) was prepared by
LiAlH4 reduction of Weinreb amide $2a)7 in 41% yield after
recrystallization $Scheme 2). As reported previously,7b
DIBAL reduction of the corresponding methyl ester caused
signi®cant racemization of the product 2b reducing the e.e.
to 13%. We ®rst used the lithium enolate of 2-undecanone
for the aldol reaction with 2b in THF at 2788C, but the
reaction was found to be non-stereoselective $76%
combined yield, 3a/3bˆ1:1.7) as already known.8,9
However, the chelation-controlled aldol reaction could be
achieved by using the zinc enolate of 2-undecanone in
CH2Cl2 at 2788C to provide syn-alcohol 3a and its anti-
isomer 3b in a ratio of 3a/3bˆ10:1 $72% combined
yield). Each isomer could be isolated by silica gel column
chromatography and their stereochemistries were con®rmed
by elaborating the major isomer 3a to preussin as described
below.
aldol reaction
HO
Ph
CHO
Ph
n-C9H19
n-C9H19
N
NH
R
O
Me
A
B
reductive
pyrrolidine
formation
Preussin
1
Scheme 1. Synthetic approach to preussin $1).
Keywords: concise synthesis; antifungal; antibacterial; cell growth inhibitor; apoptosis; preussin.
Corresponding author. Fax: 181-3-5841-8019; e-mail: atkita@mail.ecc.u-tokyo.ac.jp
p
0040±4020/01/$ - see front matter q 2001 Elsevier Science Ltd. All rights reserved.
PII: S0040-4020$01)00292-7

4108
M. Okue et al. / Tetrahedron 57 72001) 4107±4110
Scheme 2. Synthesis of preussin $1).
The hydroxyl group of 3a was protected as the TBS ether 4,
which was then treated with Ph2SiH2 or Et3GeH in the
presence of BF3´OEt2 $CH2Cl2, 2788C!rt).10 Under these
conditions, not only reductive cyclization but also desilyl-
ation took place to provide free alcohol 5 as a single stereo-
isomer4e,11 $,80±88% yield). For this reaction, TBS
protection was essential and when the nonprotected alcohol
3a was reduced directly under the same conditions, aroma-
tized pyrrole derivative 6 was obtained as the major product.
Employing Bu3SnH instead of Ph2SiH2 or Et3GeH caused
only 1,2-reduction of the ketone to give an alcohol. Finally,
reduction of the methyl carbamate of 5 with LiAlH4 gave
3.1. ꢀS)-2-Methoxycarbonylamino-3-phenylpropanal
ꢀN-methoxycarbonyl-l-phenylalaninal) ꢀ2b)
To a solution of $S)-[1-$methoxy)methylcarbamoyl-2-
phenylethyl]carbamic acid methylester7 $2a, 6.1 g,
22.9 mmol) in Et2O $230 mL) was added LiAlH4 powder
$1.1 g, 29.0 mmol) at 210 to 258C. The reaction mixture
was stirred for 2 h, and then quenched by a solution of
KHSO4 $3.2 g) in water $110 mL). The organic layer was
separated, and the aqueous layer was extracted with Et2O.
The combined organic layers were washed successively
with 3N HCl, H2O, saturated NaHCO3 solution and brine,
dried over Na2SO4 and concentrated. The residue was
recrystallized from Et2O-hexane to give 2b as a colourless
25
preussin $1) as a single stereoisomer {83%, ‰aŠ ˆ129.38 $c
D
25
1.17, CHCl3), [natural 1, ‰aŠ ˆ122.08 $c 1.0, CHCl3)]}.
D
The 1H and 13C NMR spectral data of the synthetic material
powder $2.7 g, 41%). mp 78±808C; ‰aŠ ˆ242.38 $c 1.01,
25
D
MeOH); IR $KBr) 3336, 3032, 2951, 1741, 1693, 1542,
were identical with those of natural 1.2
1
1271, 1071, 703 cm21; H NMR $CDCl3, at 558C) d 3.10
In conclusion, a short-step and stereoselective synthesis of
preussin $1) was accomplished by using a stereoselective
aldol reaction followed by reductive pyrrolidine formation
of the resulting keto amide. The overall yield was 16% over
®ve steps.
$br. d, 2H, Jˆ6.1Hz), 3.67 $s, 3H), 4.46 $br. m, 1H), 5.12 $br.
m, 1H), 7.15±7.31 $m, 5H), 9.62 $s, 1H); EIMS m/z 207
$M1); HRMS $EI) m/z calc. for C22H13NO3 207.0895,
found 207.0851.
3.2. ꢀ2S,3S)-3-Hydroxy-2-methoxycarbonylamino-1-
phenyltetradecan-5-one ꢀ3a)
3. Experimental
A solution of lithium bis$trimethylsilyl)amide $1.0 M in
hexane, 1.1 mL, 1.10 mmol) in dry CH2Cl2 $3.0 mL) was
cooled to 2788C, and a solution of 2-undecanone
$210 mL, 1.02 mmol) in dry CH2Cl2 $3.0 mL) was added
dropwise over 20 min. The reaction was stirred at 2788C
for 50 min, and a solution of ZnCl2 $1.0 M in Et2O, 1.0 mL,
1.00 mmol) was introduced dropwise over 15 min. After
15 min, a solution of 2b $99 mg, 0.349 mmol) in dry
CH2Cl2 $2.0 mL) was added. After the mixture was stirred
at 2788C for 15 min, the reaction was quenched by a drop-
wise addition of a solution of acetic acid $90 mL) in Et2O
$2.0 mL). The mixture was allowed to warm to room
temperature, and was diluted with EtOAc. The organic
layer was washed successively with 1N HCl, water, satu-
rated NaHCO3 solution and brine, dried over MgSO4 and
Melting point was measured using a BuÈchi 535 melting
point apparatus and is uncorrected. Infrared spectra were
recorded on a Jasco FT/IR-620 spectrometer. 1H NMR
spectra were recorded on a JEOL JNM-A500 spectrometer
$500 MHz). 13C NMR spectrum was recorded on a Bruker
AM300 spectrometer $75 MHz). Chemical shifts are
reported in d ppm and referenced to the residual proton
signal for CDCl3 $7.24 ppm) or DMSO-d6 $2.49 ppm) and
to internal CDCl3 $13C, 77.0 ppm). Speci®c rotations were
measured with a Jasco DIP-1000 polarimeter. Mass spectra
were obtained with a JEOL JMS-AX505WA instrument.
Column chromatography was performed with MERCK
silica gel 60 $0.063±0.200 mm) or FUJI SILYSIA
CHEMICAL LTD. Chromatorexw NH $100±200 mesh).

M. Okue et al. / Tetrahedron 57 72001) 4107±4110
4109
concentrated. The residue was puri®ed by chromatography
$Chromatorexw NH, hexane:CH2Cl2:Et2Oˆ2:2:1) to give
3a as a colourless oil $87 mg, 66%) and 3b $9.0 mg,
Jˆ12.2, 6.7, 6.7 Hz), 2.66 $dd, 1H, Jˆ14.0, 6.7 Hz), 3.02
$dd, 1H, Jˆ14.0, 6.1 Hz), 3.36 $s, 3H), 3.62 $dddd, 1H, Jˆ
9.2, 7.3, 7.3, 4.3 Hz), 3.98$dd, 1H, Jˆ13.4, 6.7 Hz), 4.15
$m, 1H), 4.84 $d, 1H, Jˆ4.3 Hz), 7.13±7.23 $m, 5H);
FABMS m/z 362 $M11); HRMS $FAB) m/z calcd for
C22H36NO3 362.2695, found 362.2681.
25
6.8%). 3a: ‰aŠ ˆ244.38 $c 0.62, CHCl3); IR $neat) 3349,
D
1
2922, 2852, 1698, 1533, 1250, 1051, 705 cm21; H NMR
$CDCl3, at 558C) d 0.87 $t, 3H, Jˆ7.3 Hz), 1.24 $m, 12H),
1.52 $m, 2H), 2.35 $dd, 1H, Jˆ7.3, 7.3 Hz), 2.50 $br. d, 1H,
Jˆ17.7 Hz), 2.60 $dd, 1H, Jˆ17.7, 9.8Hz), 2.90 $m, 2H),
3.42 $m, 1H), 3.63 $s, 3H), 3.72 $m, 1H), 4.01 $dd, 1H,
Jˆ9.8, 1.8 Hz), 5.03 $br. d, 1H, Jˆ10.0 Hz), 7.17±7.28
$m, 5H); FABMS m/z 378$M 11); HRMS $FAB) m/z
calcd for C22H36NO4 378.2644, found 378.2648. 3b:
3.5. ꢀ2S,3S,5R)-2-Benzyl-3-hydroxy-1-methyl-5-nonyl-
azolidine [ꢀ1)-Preussin ꢀ1)]
To a solution of 5 $394 mg, 1.09 mmol) in THF $10 mL) was
added LiAlH4 powder $60 mg, 1.58mmol) at room tempera-
ture. After the reaction mixture was heated and re¯uxed for
2 h, it was cooled to 08C and quenched by addition of
saturated NH4Cl solution. The resulting mixture was diluted
with EtOAc. The organic layer was washed successively
with 2N NaOH, water and brine, dried over Na2SO4 and
concentrated. The residue was puri®ed by chromatography
$Chromatorexw NH, hexane:EtOAcˆ3:1) to give 1 as a
25
‰aŠ ˆ116.38 $c 0.57, CHCl3); IR $neat) 3323, 2921,
D
2851, 1697, 1543, 1267, 1038, 704 cm21
;
1H NMR
$CDCl3, 558C) d 0.87 $t, 3H, Jˆ6.7 Hz), 1.26±1.29 $m,
12H), 1.54 $m, 2H), 2.38$m, 2H), 2.55 $dd, 1H, Jˆ17.7,
8.5 Hz), 2.63 $dd, 1H, Jˆ17.7, 3.1 Hz), 2.84 $dd, 1H,
Jˆ14.0, 7.9 Hz), 2.96 $dd, 1H, Jˆ14.0, 4.9 Hz), 3.42 $m,
1H), 3.57 $s, 3H), 3.84 $m, 1H), 3.98 $m, 1H), 4.63 $m, 1H),
7.19±7.29 $m, 5H); FABMS m/z 378$M 11); HRMS $FAB)
m/z calcd for C22H36NO4 378.2644, found 378.2648.
25
D
colourless oil $288 mg, 83%). ‰aŠ ˆ129.38 $c 1.17,
CHCl3); IR $neat) 3429, 2925, 2853, 2785, 1496, 1455,
1
1348, 1133, 1030, 929, 743, 966 cm21; H NMR $CDCl3)
3.3. ꢀ2S,3S)-3-tert-Butyldimethylsilyloxy-2-methoxy-
carbonylamino-1-phenyltetradecan-5-one ꢀ4)
d 0.83 $t, 3H, Jˆ7.0 Hz), 1.21 $m, 14H), 1.35 $ddd, 1H,
Jˆ14.0, 6.1, 1.2 Hz), 1.66 $m, 2H), 1.78$m, 1H), 2.06 $m,
1H), 2.13 $ddd, 1H, Jˆ14.0, 9.2, 6.1 Hz), 2.21 $ddd, 1H,
Jˆ9.2, 5.5, 3.7 Hz), 2.28$s, 3H), 2.79 $dd, 1H, Jˆ13.4,
5.5 Hz), 2.81 $dd, 1H, Jˆ13.4, 9.2 Hz), 3.74 $m, 1H),
7.13±7.25 $m, 5H); 13C NMR $CDCl3) d 14.1, 22.7, 26.3,
29.3, 29.5, 29.6, 29.9, 31.9, 33.6, 34.9, 38.6, 39.3, 65.8,
70.4, 73.6, 126.0, 128.3, 129.3, 139.4; FABMS m/z 318
$M11); HRMS $FAB) m/z calcd for C21H35NO 318.2797,
found 318.2802.
Imidazole $20 mg, 0.294 mmol) and TBDMSCl $35 mg,
0.232 mmol) were added to a solution of 3a $55 mg,
0.146 mmol) in DMF $1.0 mL) at 08C. After the solution
was stirred at room temperature for 1 day, water was
added and the resulting mixture was concentrated in
vacuo. The residue was diluted with EtOAc. The organic
layer was washed successively with dilute HCl, water, satu-
rated NaHCO3 and brine, dried over MgSO4 and concen-
trated. The residue was puri®ed by chromatography on
silica gel $hexane:Et2Oˆ3:1) to give 4 as a colourless oil
Acknowledgements
25
D
$59 mg, 83%). ‰aŠ ˆ212.38 $c 1.24, CHCl3); IR $neat)
3341, 2927, 2855, 1715, 1508, 1253, 1069, 836, 778,
We thank Professor M. Yoshida and Dr K. Kasahara of the
University of Tokyo for a generous gift of natural preussin
and discussions. This work was supported by a Grant-in-Aid
for Scienti®c Research from the Japanese Ministry of
Education, Science, Culture and Sports. We also thank
Sankyo Foundation of Life Science for ®nancial support.
1
699 cm21; H NMR $CDCl3, at 558C) d 0.00 $s, 3H), 0.10
$s, 3H), 0.84 $t, 3H, Jˆ6.7 Hz), 0.90 $s, 9H), 1.23±1.28$m,
12H), 1.49 $m, 2H), 2.29 $m, 2H), 2.48$dd, 1H, Jˆ17.1,
5.5 Hz), 2.62 $m, 1H), 2.68$dd, 1H, Jˆ14.0, 8.5 Hz), 2.82
$dd, 1H, Jˆ14.0, 6.1 Hz), 3.52 $br. s, 3H), 3.85 $br. m, 1H),
4.28$br. m, 1H), 4.73 $br. m, 1H), 7.13±7.24 $m, 5H);
FABMS m/z 492 $M11); HRMS $FAB) m/z calcd for
C28H50NO4Si 492.3509, found 492.3516.
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