Enzymatic oxidation of thioanisoles: Isolation and absolute configuration of metabolites

Article abstract of DOI:10.1016/j.tetasy.2004.06.050

Oxidation of p-bromothioanisole with toluene dioxygenase provides the corresponding diene diol 2 in good yield. Electrochemical reduction of 2 gives access to diene diol 3, which is not accessible by direct bio-oxidation of thioanisole. Absolute configura

Full text of DOI:10.1016/j.tetasy.2004.06.050

Tetrahedron:
Asymmetry
Tetrahedron: Asymmetry 15 (2004) 2833–2836
Enzymatic oxidation of thioanisoles: isolation and
absolute configuration of metabolites
*
ˇ
Kevin J. Finn, Petr Cankar, Timothy R. B. Jones and Tomas Hudlicky
Department of Chemistry, Brock University, St. Catharines, Ontario, Canada L2S 3A1
Received 24May 2004; accepted 17 June 2004
Available online 12 September 2004
This paper is dedicated to Professor Peter Stanetty on the occasion of his 60th birthday
Abstract—Oxidation of p-bromothioanisole with toluene dioxygenase provides the corresponding diene diol 2 in good yield. Electro-
chemical reduction of 2 gives access to diene diol 3, which is not accessible by direct bio-oxidation of thioanisole. Absolute config-
uration and enantiomeric purity are reported for the new metabolites.
Ó 2004 Elsevier Ltd. All rights reserved.
1. Introduction
SMe
SMe
SMe
OH
OH
OH
OH
The oxidation of sulfur-containing compounds by vari-
ous enzymes is well documented;1 both monooxygenases
and dioxygenases convert divalent sulfur to sulfoxides
with high enantiomeric excess.2 The prokaryotic dioxy-
genases, which process aromatic compounds to cis-
dihydrodiols,3 have shown remarkable selectivity in
the oxidations of thiophene4 and benzothiophene4b,5 to
the corresponding cis-diols, in most cases without
attendant oxidation of the sulfur atom.
Br
1
Br
2
3
E+
SO2Me
OH
In connection with our study of selective electrochemical
reduction of halogen versus sulfur functionalities, we
became interested in halothioanisoles such as 1, whose
metabolites would be amenable to a variety of further
reactions, as indicated in Figure 1. For example, oxida-
tion of the thioether in diene diol 2 would provide sulf-
O
Nu-
Br
4
Figure 1. Oxidation of p-bromothioanisole and reactive options in
metabolites.
one
4 in which each carbon could be further
functionalized by selective operations on the vinylsulf-
one moiety6 as well as by tethered radical cyclizations7
of the vinyl bromide. We were also interested in the
directing effects of the thiomethyl group on the stereo-
chemistry of the oxidation. In a review published in
1998 Boyd proposed that the larger of the two groups
in p-substituted arenes directs the oxidation with a 2,3-
regiochemistry and b-stereochemistry.8 In this manu-
script we report the synthesis, absolute configuration,
and enantiomeric purity of diol 2 as well as the synthesis
of diol 3, which cannot be obtained by direct bio-oxida-
tion of thioanisole with toluene dioxygenase.
2. Results and discussion
*
Corresponding author. Tel.: +1 905 688 5550x4956; fax: +1 905 984
4841; e-mail addresses: jonesy@chemiris.labs.brocku.ca; thudlicky@
brocku.ca
Boyd prepared the unstable diol 3 chemically from the
homochiral diol 5 in a very low yield (ꢀ10–14%)9
To whom correspondence regarding 19F NMR should be addressed.
0957-4166/$ - see front matter Ó 2004Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetasy.2004.06.050

2834
K. J. Finn et al. / Tetrahedron: Asymmetry 15 (2004) 2833–2836
O
S Me
SMe
3
SMe
6
OH
OH
TDO
TDO
7
MeSNa
HMPA
Br
5
Br
8
O
Ph
OMe
OH
NEt3, DMAP
OH
OH
OH
O
1) PAD, AcOH
2) THSCl, imid.
PtO2, H2
Mosher's acid
chloride
CF3
OTHS
OTHS
OTHS
9
12
Raney Ni
SMe
SMe
R
SMe
OH
OR
OH
OH
toluene dioxygenase
(TDO)
PAD, AcOH
-2.7 V
Br
1
R= H
10
2
R= Br
R=
THSCl, imid.
R=
THS
3
11
H
Scheme 1.
(Scheme 1). An improvement in yield (55%) was realized
when the iodo analogue of 5 was used.10 (R)-Sulfoxide 7
was also reported by Boyd et al.11 from the fermenta-
tions of thioanisole 6 with Pseudomonas UV4.
of 15 may be the preference for a conjugate rather than
the a-addition of sodium mercaptide to the olefin, as
shown in Scheme 2.
When we subjected thioanisole 6 to whole-cell fermenta-
tion with the recombinant E. coli JM 109 (pDTG601),
an organism developed by Gibson to over-express tolu-
ene dioxygenase (TDO),12 we identified 7 as the major
product (2.5g/L, 92% enantiomeric excess)13 together
with trace amounts of 3.14 In a similar whole-cell oxida-
tion of p-bromothioanisole with GibsonÕs organism, we
obtained a relatively high yield (2.3g/L) of diol 2,15,16
isolated as a crystalline compound by ethyl acetate
extraction of the fermentation broth.17 Diol 2, unlike
3, is quite robust, probably because of the electron flow
from the two functionalities is mutually cancelled and
does not contribute to the lability of either hydroxyl.
Electrochemical reduction18 of 2 at ꢁ2.7V (Hg cathode)
gave 3, which was immediately subjected to diimide
reduction with potassium azodicarboxylate (PAD)19
and subsequently protected as the silyl ether 11. Initial
attempts to determine the absolute configuration of diol
2 were performed according to the precedent for vinyl
halides to undergo substitution by sulfur nucleophiles
by a putative addition–elimination mechanism mediated
by HMPA.20 Indeed, Boyd has reported the synthesis of
cyclohexadiene-diol 3 by treatment of homochiral diol 5
with sodium thiomethoxide in HMPA, albeit in low
yield, 1–5%10 and 10–14%.9 Under identical conditions,
diol 13 was instead converted to the regioisomer 15, the
structure and connectivity of which was tentatively as-
SMe
Br
OH
OH
OH
OH
NaSMe/HMPA
NaSMe/HMPA
5
3
Br
Br
-
OH
OH
MeS
OH
OH
MeS
OH
OH
-NaBr
14
15
13
Scheme 2.
In a second attempt to establish its absolute configura-
tion, diol 2 was converted to silyl ether 11, which was re-
duced in the presence of Raney nickel to ether 9. Finally,
homochiral diene diol 5 was partially reduced, protected
as its THS ether, and hydrogenated in the presence of
AdamsÕ catalyst to provide mono-protected diol 9,
whose physical and spectral properties were compared
with those of the material obtained from diol 2 as shown
in Scheme 1. The sample of 9 obtained from 5 had a spe-
cific rotation of +10.6; the sample isolated from Raney
nickel reduction of 11 had a specific rotation of +3.
The mass spectrum of the latter showed high molecular
weight impurities apparently transparent in H and 13C
NMR experiments as the spectra of both compounds
showed identical purity.
1
1
signed on the basis of COSY H NMR spectroscopy
(Scheme 2). A plausible explanation for the formation

K. J. Finn et al. / Tetrahedron: Asymmetry 15 (2004) 2833–2836
2835
5. (a) Boyd, D. R.; Sharma, N. D.; Boyle, R.; McMurray, B.
T.; Evans, T. A.; Malone, J. F.; Dalton, H.; Chima, J.;
Sheldrake, G. N. J. Chem. Soc., Chem. Commun. 1993, 4 9;
(b) Boyd, D. R.; Sharma, N. D.; Hempenstall, F.;
Kennedy, M. A.; Malone, J. F.; Allen, C. C. R. J. Org.
Chem. 1999, 64, 4005; (c) Boyd, D. R.; Sharma, N. D.;
Harrison, J. S.; Kennedy, M. A.; Allen, C. C. R.; Gibson,
D. T. J. Chem. Soc., Perkin Trans. 1 2001, 1264–1269; (d)
Ref. 4b.
6. For recent examples, see: (a) Back, T. G.; Parvez, M.;
Zhai, H. J. Org. Chem. 2003, 68, 9389–9393; (b) Chen, Y.;
Evarts, J. B., Jr.; Torres, E.; Fuchs, P. L. Org. Lett. 2002,
4(21), 3571–3574; (c) Craig, D. C.; Edwards, G. L.;
Muldoon, C. A. Synlett 1997, 1318–1320; For compre-
hensive reviews, see: (d) Fuchs, P. L.; Braish, T. F. Chem.
Rev. 1986, 86, 903; (e) Ba¨ckvall, J. E.; Chinchilla, R.;
To clarify the observed discrepancy in specific rotation,
we performed an additional proof of enantiomeric ex-
cess. Racemic cis-dihydroxy cyclohexane was converted
to a monothexyl derivative and further transformed to
MosherÕs ester 12, whose 19F NMR spectrum displayed
signals of equal intensity at ꢁ71.8 and ꢁ72.6ppm. Both
samples of 9 were converted to their Mosher esters and
their 19F NMR spectra displayed a single signal at
ꢁ72.8ppm. On the basis of this evidence we concluded
that 2 possesses the b-absolute configuration as indi-
cated in Scheme 1. As near as can be judged from the
absence of the diastereomeric signal in 12, the enantio-
meric excess of diol 2 is therefore greater than 95%.
We conclude that the whole-cell fermentation of p-
bromothioanisole with E. coli JM 109 (pDTG601) pro-
duced the single stereoisomer represented in Scheme 1
and that the thiomethyl group rather than the bromine
was the directing element in the biooxidation. This
observation further supports BoydÕs proposal that the
larger of the two groups on the aromatic nucleus directs
the regio- and stereochemistry of the oxidation. Further
investigation of applications of these new metabolites in
asymmetric synthesis is ongoing and will be reported in
due course.
´
Najera, C.; Yus, M. Chem. Rev. 1998, 98, 2291.
7. For an excellent review of radical cyclizations in the
synthesis of heterocycles, see: Bowman, W. R.; Fletcher,
A. J.; Potts, G. B. S. J. Chem. Soc., Perkin Trans. 1 2002,
2747–2762; For a review of free-radical annulation and
cascade reactions, see: McCarroll, A. J.; Walton, J. C. J.
Chem. Soc., Perkin Trans. 1 2001, 3215–3229.
8. Boyd, D. R.; Sheldrake, G. N. Nat. Prod. Rep., 1998,
309.
9. Boyd, D. R.; Hand, M. V.; Sharma, N. D.; Chima, J.;
Dalton, H.; Sheldrake, G. N. J. Chem. Soc., Chem.
Commun. 1991, 1630–1632.
10. Boyd, D. R.; Sharma, N. D.; Byrne, B.; Hand, M. V.;
Malone, J. F.; Sheldrake, G. N.; Blacker, J.; Dalton, H. J.
Chem. Soc., Perkin Trans. 1 1998, 1935–1943.
11. Allen, C. R. R.; Boyd, D. R.; Dalton, H.; Sharma, N. D.;
Haughey, S. A.; McMordie, R. A. S.; McMurray, B. T.;
Sheldrake, G. N.; Sproule, K. J. Chem. Soc., Chem.
Commun. 1995, 119–120.
12. Zylstra, G. J.; Gibson, D. T. J. Biol. Chem. 1989, 264,
14940.
13. Holland, H. L.; Brown, F. H.; Larsen, B. G. Biorg. Med.
Chem. Lett. 1994, 647.
14. The phenolic derivative arising from the decomposition of
thiomethyl-diene-diol 3 made by whole-cell fermentation
of thioanisole was isolated in low yield (0.15g/L) after
flash chromatography. Physical (TLC) and spectral (1H
NMR) data are consistent with that of the compound
arising from the decomposition of 3 synthesized by
electroreduction of 2.
15. For a detailed description of medium-scale whole-cell
fermentation (>10L) see: Endoma, M. E.; Bui, V. P.;
Hansen, J.; Hudlicky, T. Org. Proc. Res. Dev. 2002, 6,
525–532.
16. Diol 2 and other metabolites derived from p-substituted
thioanisoles have been prepared by enzymatic oxidations
with Pseudomonas putida UV4. See: Boyd, D. R.; Sharma,
N. D.; Byrne, B. E.; Haughey, S. A.; Kennedy, M. A.;
Allen, C. C. R. Org. Biomol. Chem., in press.
Acknowledgements
This work was funded by National Science and Engi-
neering Research Council (NSERC) of Canada, Petro-
leum Research Fund administered by the American
Chemical Society (PRF-38075-AC), Canadian Founda-
tion for Innovation (CFI), and the Canada Research
Chairs Program. We are grateful to Professor Rebecca
Parales (UC-Davis) and Dr. Gregg Whited (Genencor)
for their many helpful discussions and suggestions con-
cerning medium scale fermentation. We thank Brock
University for providing a graduate fellowship for K.F.
References
1. (a) Holland, H. L. Chem. Rev. 1988, 473–485; (b)
Colonna, S.; Gaggero, N.; Carrea, G.; Pasta, P. Chem.
Commun. 1998, 415; (c) Holland, H. L. Nat. Prod. Rep.
2001, 18, 171–181; (d) Colonna, S.; Gaggero, N.; Carrea,
G.; Pasta, P.; Alphand, V.; Furstoss, R. Chirality 2001, 13,
40–42; (e) Boyd, D. R.; Sharma, N. D.; Haughey, S. A.;
Kennedy, M. A.; Malone, J. F.; Shepherd, S. D.; Allen, C.
R.; Dalton, H. Tetrahedron 2004, 60, 549–559; (f) Boyd,
D. R.; Sharma, N. D.; Gunaratne, N.; Haughey, S. A.;
Kennedy, M. A.; Malone, J. F.; Shepherd, S. D.; Allen, C.
R.; Dalton, H. Org. Biomol. Chem. 2003, 1, 984–994.
2. (a) Boyd, D. R. J. Chem. Soc., Chem. Commun. 1995,
119–120; (b) Colonna, S.; Gaggero, N.; Carrea, G.; Pasta,
P. Chem. Commun. 1997, 439; (c) Holland, H. L. J. Ind.
Microbiol. Biotechnol. 2003, 30, 292–301.
17. The spectral and physical data for 2, 3, and 10 are as
follows: 1-Bromo-4-thiomethyl-(2R,3S)-dihydroxycyclo-
19
D
CHCl3); Rf = 0.26 (hexanes–ethyl acetate, 1:1); IR (film)
hexa-4,6-diene 2: mp 59–63°C; ½aŠ ¼ ꢁ10:0 (c 1.08,
1
3197, 2921, 1626, 1548, 1416, 1340, 1306, 1036cmꢁ1; H
3. (a) Hudlicky, T.; Gonzalez, D.; Gibson, D. T. Aldrichim.
Acta 1999, 35; (b) Boyd, D. R. Nat. Prod. Rep. 1998, 15,
309.
4. (a) Boyd, D. R.; Sharma, N. D.; Haughey, S. A.; Malone,
J. F.; McMurray, B. T.; Sheldrake, G. N.; Allen, C. C. R.;
Dalton, H. J. Chem. Soc., Chem. Commun. 1996, 2363; (b)
Boyd, D. R.; Sharma, N. D.; Gunaratne, N.; Haughey, S.
A.; Kennedy, M. A.; Malone, J. F.; Allen, C. C. R.;
Dalton, H. Org. Biomol. Chem. 2003, 1, 984–994.
NMR (400MHz, CDCl3) d: 6.37 (d, J = 6.1Hz, 1H), 5.35
(d, J = 6.3Hz, 1H), 4.43 (dd, J = 9.0, 3.2Hz, 1H), 4.32 (dd,
J = 7.5, 1.4Hz, 1H), 2.63 (d, J = 9Hz, 1H), 2.26 (s, 3H),
2.24(d, J = 7.6, 1H). 13C NMR (100MHz, CDCl3) d:
142.8, 127.8, 120.3, 112.7, 73.6, 72.5, 14.4; EI-MS m/z (%):
238 (8), 236 (8), 220 (100), 218 (98), 205 (41), 203 (39), 177
(24), 175 (24), 157 (20), 142 (25), 109 (33), 96 (24), 45 (41).
EI-HRMS calcd for C7H9O2SBr (M+): 235.9501; found:
235.9506; Anal. Calcd for C7H9BrO2S: C, 35.46; H, 3.83.

2836
K. J. Finn et al. / Tetrahedron: Asymmetry 15 (2004) 2833–2836
Found: C, 36.10; H, 3.88. After 72h in transit, diol 2 was
nes–ethyl acetate, 30:70); IR (film) 3249, 2944, 2913, 2890,
2829, 1623, 1434, 1356, 1327, 1100cmꢁ1 1H NMR
stable enough to provide the following elemental compo-
sition: Anal. Calcd for C7H9BrO2S: C, 35.46; H, 3.83.
Found: C, 36.10; H, 3.88.
;
(400MHz, CDCl3) d: 5.57 (t, J = 4Hz, 1H), 4.05 (s, 1H),
3.82 (d, J = 4.2Hz, 1H), 2.55 (d, J = 4.1Hz,1H), 2.40 (s,
1H), 2.19 (s, 3H), 2.15–2.10 (m, 1H), 1.85–1.60 (m, 3H).
13C NMR (100MHz, CDCl3) d: 134.6, 124.8, 69.4, 69.1,
25.7, 24.8, 15.1; EI-MS m/z (%): 160 (50), 142 (22), 127
(31), 116 (100), 95 (47), 87 (58), 68 (40), 55 (30), 45 (54).
EI-HRMS calcd for C7H12O2S (M+): 160.0554; found:
160.0558; Anal. Calcd for C7H12O2S: C, 52.47; H, 7.55.
Found: C, 52.74; H, 7.39.
1-Thiomethyl-(2S,3S)-dihydroxycyclohexa-4,6-diene
mp 61–62°C; ½aŠ ¼ þ81:3 (c 0.27, MeOH); Rf = 0.4
3:
24
D
(hexanes–ethyl acetate, 30:70); IR (film) 3247, 2915, 2858,
1
1551, 1545, 1431, 1420, 1321, 1292, 1106cmꢁ1; H NMR
(400MHz, CD3OD) d: 5.99 (dq, J = 5.5, 2Hz, 1H), 5.72
(dd, J = 9.5, 3.6Hz, 1H), 5.58 (d, J = 5.6Hz, 1H), 4.25 (m,
1H), 4.02 (d, J = 5.5Hz, 1H), 2.31 (s, 3H). 13C NMR
(100MHz, CD3OD) d: 141.7, 125.4, 124.5, 114.0, 71.3,
69.1, 13.0. The crystalline diol 3 was found to decompose
to its corresponding phenol at room temperature within
30min, however, in dilute dichloromethane solution at
ꢁ18°C decomposition is significantly slowed and the diol
3 survives for several weeks.
18. (a) Hudlicky, T.; Claeboe, C. D.; Brammer, L. E.;
Koroniak, L.; Butora, G.; Ghiviriga, I. J. Org. Chem.
1999, 64, 4909; (b) Hudlicky, T.; Frey, D. A.; Koroniak,
L.; Claeboe, C. D.; Brammer, L. E., Jr. Green Chem. 1999,
1, 57–59.
19. Bui, V. P.; Nguyen, M.; Hansen, J.; Baker, J.; Hudlicky,
T. Can. J. Chem. 2002, 80, 708–713.
20. Tiecco, M. J. Org. Chem. 1983, 48, 4795–4800.
1-Thiomethyl-(2S,3S)-dihydroxycyclohex-6-ene 10: mp
24
D
91–93°C; ½aŠ ¼ ꢁ104( c 0.75, CHCl3); Rf = 0.4(hexa-