Chiral auxiliaries as docking/protecting groups in biohydroxylation: (S)-specific hydroxylation of enantiopure tert-butyl-substituted spirooxazolidines derived from cyclopentanone

Article abstract of DOI:10.1002/ejoc.200400636

An enantiopure tert-butyl-substituted derivative of cyclopentanone, which is a vital member of the chiral docking/ protecting group series, is employed, for the first time, to stereoselectively (90% de) introduce an (S)-configured hydroxyl group onto an unactivated carbon atom present in the cyclopentane ring using the fungus Beauveria bassiana ATCC 7159. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005.

Full text of DOI:10.1002/ejoc.200400636

SHORT COMMUNICATION
Chiral Auxiliaries as Docking/Protecting Groups in Biohydroxylation:
(
S)-Specific Hydroxylation of Enantiopure tert-Butyl-Substituted
Spirooxazolidines Derived From Cyclopentanone
[
a]
[a]
[a]
[b]
Dieter F. Münzer, Herfried Griengl, Alexandra Moumtzi, Robert Saf,
[a]
[a]
Tullio Terzani, and Anna de Raadt*
Dedicated to the memory of Professor Herbert Holland[‡]
Keywords: Biohydroxylation / Biotransformations / Enantioselectivity / Substrate engineering
An enantiopure tert-butyl-substituted derivative of cyclo-
pentanone, which is a vital member of the chiral docking/
protecting group series, is employed, for the first time, to ster-
eoselectively (90% de) introduce an (S)-configured hydroxyl
group onto an unactivated carbon atom present in the cyclo-
pentane ring using the fungus Beauveria bassiana ATCC
7159.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2005)
Introduction
The stereoselective introduction of hydroxyl groups onto
unactivated carbon atoms present in organic compounds is,
generally, still a very daunting task in modern synthetic
[
1,2]
chemistry.
the docking/protecting (d/p) group concept as a means to
For this reason, we have been investigating
[
3,4]
easily employ biohydroxylation in preparative chemistry.
We have found that a range of organic compounds, such as
carboxylic acids, alcohols, aldehydes and ketones, can be
easily hydroxylated following this concept.
Chiral d/p groups have also been investigated[ and em-
ployed for the hydroxylation of ketones. In this manner, the
stereoselective functionalisation of these compounds was
achieved. Indeed, depending on the nature of the chiral d/
p group used, the configuration of the introduced hydroxyl
moiety could be readily determined.
5,6]
The d/p concept is a three-step process (Scheme 1). Using
parent ketone 1 and a chiral d/p group as an example, deriv-
atisation gives the enantiopure biohydroxylation substrate 2
Scheme 1. The d/p concept as exemplified by a chiral d/p group and
model ketone 1: step 1: (2R)-2-amino-1-propanol, K CO , CH Cl ,
2 3 2 2
in the first step. Subsequent exposure of this spirooxazolid- 20 °C, 24 h, followed by BzCl, 20 °C, 24 h; step 2: Beauveria bassi-
ana ATCC 7159; step 3: BnBr, NaH, THF/DMF, 20 °C followed
+
by IR 120 (H , cat), CH
3
CN, 20 °C
[
[
[
a]
b]
‡]
Institut für Organische Chemie der Technischen Universität
Graz,
Stremayrgasse 16, 8010 Graz, Austria
Fax: +43-316-873-8740
ine derivative to a suitable microorganism, for example
Beauveria bassiana ATCC 7159, yields hydroxylated pro-
duct 3. The third and final step of this approach is to re-
move the d/p group to furnish the desired hydroxylated pro-
duct 4. In this particular example, an atypical protection
step (benzylation) was also needed to prevent elimination
of the introduced group.
E-mail: deraadt@orgc.tu-graz.ac.at
Institut für Chemische Technologie Organische Stoffe der Tech-
nischen Universität Graz,
Stremayrgasse 16, 8010 Graz, Austria
Fax: +43-316-873-8959
E-mail: robert.saf@TUGraz.at
Not only a leader in the field of biohydroxylation but a most
valued friend and colleague
Eur. J. Org. Chem. 2005, 793–796
DOI: 10.1002/ejoc.200400636
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
793

D. F. Münzer, H. Griengl, A. Moumtzi, R. Saf, T. Terzani, A. de Raadt
SHORT COMMUNICATION
Despite the fact that a wide range of chiral d/p groups point that, based on published experiments[5] with product
has been investigated, while the (R)-configured product (3) 3, this ee value should increase after simple recrystallisation
could be prepared in 90% de − recrystallisation increased of compound 9. This result nicely complements those ob-
this value to over 99% − the (S)-configured counterpart tained from the (R)-methyl d/p used in previous studies
could not be obtained with more than 20% de from other (Scheme 1) where product 3 could be obtained in 90% de
substrates.
in a single biohydroxylation step.
In this account we wish to disclose results obtained from
the last member of this chiral d/p group series, namely com-
pounds containing tert-butyl substituents. In this manner,
the synthesis of the (S)-configured biohydroxylation pro-
duct could be accomplished with 90% de.
Results and Discussion
The commercially available, but relatively expensive, tert-
butyl amino alcohols 5 and 6 required for substrate synthe-
sis could be easily prepared from the corresponding cheaper
amino acids in high yield (over 80%) by the reduction
method reported by Drauz and coworkers.[ Subsequent re-
action with cyclopentanone afforded the desired, enantiop-
7]
Scheme 3. Biohydroxylation of tert-butyl substrates 7 and 8, subse-
quent benzylation and d/p removal: step 1: Beauveria bassiana
ure substrates 7 and 8, respectively (Scheme 2). In contrast ATCC 7159; step 2: BnBr, NaH, THF/DMF, 20 °C followed by IR
to previous observations, these compounds were obtained 120 (H , cat), CH
+
3
CN, 20 °C
in only modest yields under standard, unoptimized condi-
[
5,8]
tions
(22% and 17%, respectively).
Conclusions
In conclusion, it has been shown that, for the biohydrox-
ylation step, the appropriate choice of chiral d/p group can
be exploited to obtain either configuration of the newly in-
troduced alcohol in 90% de. Simple recrystallisation of this
biohydroxylation product could improve this value to over
99% de if desired. Simple removal of the chiral d/p group
yields the corresponding ketone derivative.
Experimental Section
General Remarks: Please refer to ref.[3] for all general methods un-
Scheme 2. Preparation of enantiopure tert-butyl biohydroxylation
substrates 7 and 8: step 1: NaBH , I , THF; step 2: cyclopentanone,
CO , CH Cl , 20 °C, 24 h followed by BzCl, 20 °C, 24 h
4
2
less stated otherwise. NMR: signals from the minor isomer are
K
2
3
2
2
1
3
given in italics. The C NMR spectra for spirooxazolidine deriva-
tives 7 to 13 suggested that a number of different conformations
For the biohydroxylation step, the fungus Beauveria bas- were present in the NMR sample (see Figure 1 for numbering
scheme).
siana ATCC 7159 was then employed in the usual manner
to afford crystalline products 9 and 10 in modest yields
(50% and 22%, respectively; Scheme 3). We believe that this
outcome could be improved by optimising the fermentation
parameters if required.[ More importantly, however, the de
and configuration of the introduced alcohol were deemed
to be very interesting. While the de of product 10 was found
to be rather modest (18%) by HPLC, compound 9 exhib-
ited a high de of 90%. After subsequent benzylation and d/
9]
Figure 1. Numbering scheme for the spirooxazolidine derivatives
p group removal, the configuration of the newly introduced Amino Alcohols 5 and 6: H and 13C NMR spectroscopic data, op-
1
chiral center could be determined by GC comparison of the tical rotations and melting points were in agreement with published
values.[
10]
resulting ketones 4 and 11 with model compounds.
Satisfyingly, although ketone 4 was found to be (R)-config-
Spirooxazolidine Derivative 7: Employing the standard procedure
ured (19% ee), ketone 11 was found to be (S)-configured for preparing spirooxazolidine derivatives,[ compound 7 was pre-
5]
and with a high ee (89%). It should be mentioned at this pared in 22% yield as a pale-yellow, crystalline solid. M.p. 97.0–
794
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 793–796

Chiral Auxiliaries as Docking/Protecting Groups in Biohydroxylation
SHORT COMMUNICATION
9
=
7
7.5 °C. [α]20
D
= +65.3 (c = 1.11 in CH
2
Cl
2
). H NMR (CDCl
1
3
): δ
a
7-H), 4.45 (br. s, 2 H, CH
NMR (CDCl ): δ = 27.4 (C-11, C-12, C-13), 31.3, 36.0 (2×br. s,
2
Ph), 7.24 (m, 10 H, COPh) ppm. 13
C
0.72 (br. s, 9 H, 11-H, 12-H, 13-H), 1.40–2.10 (br. m, 6 H, 6 -H,
-H, 8-H, 9 -H), 2.28, 2.73 (2×br. m, 2×1 H, 6 -H, 9 -H), 3.95 C-6, C-9), 35.6 (C-10), 42.4 (br. s, C-8) 65.8, 66.3 (2×br. s, C-2, C-
3
a
b
b
13
(m, 3 H, 2-H, 3-H), 7.38 (s, 5 H, COPh) ppm. C NMR (CDCl
3 2
): 3), 70.7 (CH Ph), 79.8 (br. s, C-7) 104.6 (br. s, C-5), 127.0, 127.5,
δ = 24.7, 25.2 (2×br. s, C-7, C-8), 27.4 (C-11, C-12, C-13), 35.2,
127.6, 127.8, 128.4, 128.7 129.9, 131.4, 138.6, 139.0 (COPh) ppm.
+
+
3
3
7.5 (2×br. s, C-6, C-9), 35.7 (C-10), 65.5, 66.2 (2×br. s, C-2, C-
MS (70 eV): m/z (%) = 393 (3) [M] , 364 (1) [M – C
2
H
5
] , 336 (3)
+
), 105.7 (C-5), 127.7, 128.4, 129.9, 138.8 (COPh), 170.2 (COPh)
[M – C
4
H
9
] , 287 (5), 258 (9), 245 (7), 214 (5), 182 (4), 146 (4), 124
+
+
+
+
+
2 5
ppm. MS (70 eV): m/z (%) = 287 (15) [M] , 258 (13) [M – C H ] , (5), 105 (100) [Bz] , 91 (37) [Bn] , 77 (28) [Ph] . HRMS: calcd.
+
+
+
230 (43) [M – C
4
H
9
] , 105 (100) [Bz] , 77 (16) [Ph] . HRMS: calcd.
393.23039; found 393.23040.
287.1885; found 287.1887.
Spirooxazolidine Derivative 8: Employing the standard procedure
for preparing spirooxazolidine derivatives,[ compound 8 was pre-
pared in 17% yield as a pale-yellow, crystalline solid. M.p. 92.0–
5]
5.0 °C. [α]2
0
= –57.8 (c = 1.51 in CH
1
9
=
7
(
D
2 2 3
Cl ). H NMR (CDCl ): δ
a
0.72 (br. s, 9 H, 11-H, 12-H, 13-H), 1.40–2.10 (br. m, 6 H, 6 -H,
a
b
b
-H, 8-H, 9 -H), 2.28, 2.73 (2×br. m, 2×1 H, 6 -H, 9 -H), 3.95
13
Figure 2. Compounds 12 and 13
m, 3 H, 2-H, 3-H), 7.38 (s, 5 H, COPh) ppm. C NMR (CDCl
3
):
δ = 24.7, 25.2 (2×br. s, C-7, C-8), 27.4 (C-11, C-12, C-13), 35.2,
3
3
2
7.5 (2×br. s, C-6, C-9), 35.7 (C-10), 65.5, 66.2 (2×br. s, C-2, C-
Compound 13: Standard benzylation[5] of 10 (73 mg) furnished de-
), 127.7, 128.4, 129.9, 138.8 (COPh) ppm. MS (70 eV): m/z (%) =
rivative 13 (83.9 mg; Figure 2) in 89% yield as a pale-yellow syrup.
+
+
+
87 (15) [M] , 258 (12) [M – C
2
H
5
] , 230 (43) [M – C
4
H
9
] , 105
1
H NMR (CDCl
.13, 2.55, 3.08 (4×m, 6 H, 6-H, 8-H, 9-H, OH), 3.60, 3.95 (2×m,
3 H, 2-H, 3-H), 4.18 (m, 1 H, 7-H), 4.45 (br. s, 2 H, CH Ph), 7.24
3
): δ = 0.65 (br. s, 9 H, 11-H, 12-H, 13-H), 1.72,
+
+
(100) [Bz] , 77 (17) [Ph] . HRMS: calcd. 287.1885; found 287.1875.
2
Biohydroxylation Product 9: Employing published methods,[5] treat-
ment of compound 7 (1.277 g) with Beauveria bassiana ATCC 7159
gave the title compound (586.6 mg), together with unreacted start-
ing material (97.1 mg), as a white solid (50% yield, taking into
account unreacted starting material). M.p. 89.0–104.0 °C. [α]
+
=
2
1
3
(m, 10 H, COPh) ppm. C NMR (CDCl
C-13), 31.3, 36.0 (2×br. s, C-6, C-9), 35.6 (C-10), 42.5, 43.9 (2×br.
s, C-8) 65.8, 66.3 (2×br. s, C-2, C-3), 70.6, 71.3 (CH Ph), 79.3,
79.8 (2×br. s, C-7) 104.6 (br. s, C-5), 127.0, 127.5, 127.8, 127.8,
); 90% de (HPLC: CHIRALCEL AD, T 128.4, 128.7 130.0, 131.5, 138.6, 139.0 (COPh) ppm. MS (70 eV):
m/z (%) = 393 (2) [M] , 364 (1) [M – C H ] , 336 (2) [M – C H ]
3
): δ = 27.4 (C-11, C-12,
2
2
0
D
=
2 2
79.4 (c = 1.06 in CH Cl
–1
+
+
10 °C, 0.5 mL min , n-heptane/IPA = 4:1, measured at 238 nm),
2
5
4
9
+
retention time of (3S,5Ξ,7R)-9 = 17.6 min, retention time of
, 287 (3), 258 (5), 245 (4), 214 (3), 182 (2), 146 (5), 124 (2), 105
(100) [Bz] , 91 (49) [Bn] , 77 (25) [Ph] . HRMS: calcd. 393.23039;
1
+
+
+
3
(3S,5Ξ,7S)-9 = 20.8 min. H NMR (CDCl ): δ = 0.72 (br. s, 9 H,
1
4
1-H, 12-H, 13-H), 1.65–2.90 (3×br. m, 7 H, 6-H, 8-H, 9-H, OH), found 393.22975.
.00 (br. m, 3 H, 2-H, 3-H), 4.39 (br. s, 1 H, 7-H), 7.39 (s, 5 H,
Ketones 4 and 11: The known[5] title compounds were obtained for
chiral GC experiments from the corresponding benzylated deriva-
13
COPh) ppm. C NMR (CDCl
5.3 (2×br. s, C-6, C-9), 35.6 (C-10), 42.7 (br. s, C-8), 65.8 (br. s,
C-2, C-3), 73.4 (br. s, C-7), 105.0 (br. s, C-5), 127.6, 128.4, 130.0,
3
): δ = 27.4 (C-11, C-12, C-13), 34.3,
3
[3]
tives 13 and 12, employing published conditions. These com-
pounds were then compared with reference substances available
from previous studies.
+
1
38.4 (COPh) ppm. MS (70 eV): m/z (%) = 303 (12) [M] , 286 (2)
+
+
+
[
M – OH] , 274 (10) [M – C
2 5
H ] , 258 (16), 246 (28) [M – C
H
4 9
] ,
+
+
124 (42), 105 (100) [Bz] , 77 (27) [Ph] . HRMS: calcd. 303.1834;
found 303.1831.
Acknowledgments
Biohydroxylation Product 10: Employing published methods,[5]
treatment of compound 8 (759.6 mg) with Beauveria bassiana
ATCC 7159 gave the title compound (160.6 mg), together with un-
reacted starting material (65.8 mg), as a white solid (22% yield,
taking into account unreacted starting material). M.p. 85.0–
Financial support from Spezialforschungsbereich F001 Biokatalyse
is gratefully acknowledged. The authors also wish to express their
thanks to B. Fetz, H.-J. Weber and C. Illaszewicz for their technical
assistance.
1
0
05.0 °C; 18% de (HPLC, CHIRALCEL OD-H, T = 10 °C,
.5 mL/min, n-heptane/IPA = 7:2, measured at 238 nm), retention
[1] D. H. R. Barton, Tetrahedron 1998, 54, 5805–5817.
time of (3R,5Ξ,7S)-9 = 16.0 min, retention time of (3R,5Ξ,7R)-9 = [2] G. Asensio, R. Mello, M. E. González-Núnez, G. Castellano,
1
2
2.1 min. H NMR (CDCl
3
): δ = 0.72 (br. s, 9 H, 11-H, 12-H, 13-
J. Corral, Angew. Chem. 1996, 108, 196–198; Angew. Chem. Int.
Ed. 1996, 35, 217–218.
H), 1.65–2.90, 3.12 (4×m, 7 H, 6-H, 8-H, 9-H, OH), 4.00 (m, 3 H,
-H, 3-H), 4.39 (br. m, 1 H, 7-H), 7.39 (s, 5 H, COPh) ppm.
NMR (CDCl ): δ = 27.4 (C-11, C-12, C-13), 34.4, 34.8, 35.3 (3×br.
3
s, C-6, C-9), 35.7 (C-10), 42.7, 46.0 (2×br. s, C-8), 66.0 (br. s, C-2,
C-3), 73.5 (br. s, C-7), 127.6, 128.5, 130.1, 138.4 (COPh) ppm. MS
70 eV): m/z (%) = 303 (11) [M] , 286 (2) [M – OH] , 274 (10) [M –
] , 258 (13), 246 (27) [M – C
7 (26) [Ph] . HRMS: calcd. 303.1834; found 303.1841.
1
3
[3] G. Braunegg, A. de Raadt, S. Feichtenhofer, H. Griengl, I.
Kopper, A. Lehmann, H. Weber, Angew. Chem. Int. Ed. 1999,
2
C
3
8, 2763–2766.
4] A. de Raadt, H. Griengl, H. Weber, Chem. Eur. J. 2001, 7, 27–
1.
[
[
3
+
+
(
C
7
5] A. de Raadt, B. Fetz, H. Griengl, M. F. Klingler, I. Kopper,
B. Krenn, D. F. Münzer, R. G. Ott, P. Plachota, H. Weber, G.
Braunegg, W. Mosler, R. Saf, Eur. J. Org. Chem. 2000, 3835–
+
+
+
2
H
5
4
H
9
] , 124 (40), 105 (100) [Bz] ,
+
3847.
Compound 12: Standard benzylation[5] of 9 (135.0 mg) furnished
derivative 12 (146.2 mg; Figure 2) in 83% yield as a pale-yellow
[
6] A. de Raadt, B. Fetz, H. Griengl, M. F. Klingler, B. Krenn, K.
Mereiter, D. F. Münzer, P. Plachota, H. Weber, R. Saf, Tetrahe-
dron 2001, 57, 8151–8157.
[7] M. J. McKennon, A. I. Meyers, K. Drauz, M. Schwarm, J. Org.
Chem. 1993, 58, 3568–3571.
syrup. [α]2
0
= +65.5 (c = 1.90 in CH
.65 (br. s, 9 H, 11-H, 12-H, 13-H), 1.72, 2.13, 2.55 (3×m, 6 H, 6-
H, 8-H, 9-H, OH), 3.60, 3.95 (2×m, 3 H, 2-H, 3-H), 4.18 (m, 1 H,
1
D
2 2 3
Cl ). H NMR (CDCl ): δ =
0
Eur. J. Org. Chem. 2005, 793–796
www.eurjoc.org
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
795

D. F. Münzer, H. Griengl, A. Moumtzi, R. Saf, T. Terzani, A. de Raadt
SHORT COMMUNICATION
[
8] A number of reaction variables, such as reaction temperature,
reaction solvent and order of reagent addition, were examined
in an effort to improve the yields of compounds 7 and 8.
9] An example of how fermentation conditions can influence a
product yield and optical purity can be found in the following
reference: A. Kraemer-Schafhalter, S. Domenek, H. Boehling,
S. Feichtenhofer, H. Griengl, H. Voss, Appl. Microbiol. Biotech.
2000, 53, 266–271.
[10] Aldrich Handbook and Fine Chemicals and Laboratory Equip-
ment (2003–2004), Sigma–Aldrich Co.
[
Received: September 7, 2004
796
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
Eur. J. Org. Chem. 2005, 793–796