Structural characterization of 1β,11α-dihydroxycanrenone biotrans-formed from canrenone by Aspergillus ochraceus SIT34205

Article abstract of DOI:10.1016/j.cclet.2012.01.003

Canrenone (1) was biotransformed into 11α-hydroxycanrenone (2) and a main byproduct (3) by Aspergillus ochraceus SIT34205. Compound 3 was separated and purified using silica gel column chromatography, and its structure was characterized via MS and NMR methods. These results indicated that 3 was 1β,11α-dihydroxycanrenone and the product of further hydroxylation of 2. Thus, investigating the structure and synthesis of 3 may be a promising method to improve the efficiency and purity of 2.

Full text of DOI:10.1016/j.cclet.2012.01.003

Available online at www.sciencedirect.com
Chinese Chemical Letters 23 (2012) 313–316
www.elsevier.com/locate/cclet
Structural characterization of 1b,11a-dihydroxycanrenone
biotrans-formed from canrenone by Aspergillus ochraceus
SIT34205
a
a
a
Shao Feng Rong a, , Xiao Li Zhang , Bao Mei Ding , Yi Fei Wang ,
*
Xian Hua Pan a, Jian Zhang a, Yi Shen b
a Department of Bioengineering, Shanghai Institute of Technology, Shanghai 201400, China
b Division of Antibiotics, Shanghai Institute for Food and Drug Control, Shanghai 200233, China
Received 19 September 2011
Available online 7 February 2012
Abstract
Canrenone (1) was biotransformed into 11a-hydroxycanrenone (2) and a main byproduct (3) by Aspergillus ochraceus
SIT34205. Compound 3 was separated and purified using silica gel column chromatography, and its structure was characterized
via MS and NMR methods. These results indicated that 3 was 1b,11a-dihydroxycanrenone and the product of further
hydroxylation of 2. Thus, investigating the structure and synthesis of 3 may be a promising method to improve the efficiency
and purity of 2.
# 2012 Shao Feng Rong. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
Keywords: Aspergillus ochraceus; Biotransformation; Canrenone; 1b,11a-Dihydroxycanrenone
11a-Hydroxycanrenone (2) is used mainly as a pharmaceutical intermediate for synthesizing eplerenone,
which has cardiovascular protective effects [1,2]. In the semi-chemical synthesis of eplerenone from canrenone (1),
11a-hydroxylation of 1 by microbial transformation is the first step and one of the most critical steps [3].
Reactions involved in microbial transformation for the production of steroid agents typically include
hydroxylation, dehydrogenation, and sterol side-chain cleavage, among others [4,5]. The most important reaction
directed to microbial transformation of steroid compounds is the hydroxylation reaction. A number of microorganisms
in nature are capable of transformation via 11a-hydroxylation of steroids, and most of them are molds [6]. Aspergillus
ochraceus is used extensively to convert 1 into 2. In the middle and late stages of the biotransformation, a main
byproduct (3) with a polarity that was very close to that of 2 was previously found. Compound 3 caused inconvenience
to the purification of 2, which, in turn, was disadvantageous to the chemical synthesis of highly pure eplerenone. The
production and the preparative processes of 2 have been reported previously [7,8]. However, to the best of our
knowledge, no reports on 3 have been published. In the present study, we aim to identify the structure of 3 in order to
clarify the process of microbial conversion of 2 from 1 by A. ochraceus SIT34205.
* Corresponding author.
E-mail address: rsf1778@yahoo.com.cn (S.F. Rong).
1001-8417/$ – see front matter # 2012 Shao Feng Rong. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.
doi:10.1016/j.cclet.2012.01.003

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S.F. Rong et al. / Chinese Chemical Letters 23 (2012) 313–316
1. Experimental
Strain and culture media: A. ochraceus SIT34205 was obtained and screened by our laboratory. The composition of
the slant culture medium (g/L) was as follows: Corn steep liquor 10, tryptone 10, and agar 25. The composition of seed
culture medium (g/L) was as follows: Glucose 20, yeast extract 15, fish peptone 5, corn starch 5, corn steep liquor 0.5,
and KH2PO4 0.5. The composition of biotransformation medium (g/L) was as follows: glucose 25, yeast extract 15,
peptone 5, and KH2PO4 0.5.
Biotransformation of 2 from 1: Strain SIT34205 was cultured in slant medium at 28 8C for 5–7 days, and transferred
into sterile physiological saline to obtain a spore suspension at a concentration of 1 ꢀ 107 spores/mL. The suspension
was inoculated into a 100 mL seed culture medium in a 500 mL shake flask, cultured at 28 8C and 160 rpm/min for
20 h. The seed culture was inoculated into the biotransformation medium in an amount of 4% and cultured for 20 h,
followed by the addition of 10 g/L of 1. Incubation was continued for 50 h under the same conditions.
HPLC assay of 2 and 3: A RP C18 column (Dikma Diamonsil C18, 250 mm ꢀ 4.6 mm, 5 mm) was used as
chromatographic column. The wavelength for detection was 280 nm, mobile phase was methanol–water (7:3, v/v),
injection volume was 10 mL, column temperature was 25 8C, and flow rate was 1 mL/min.
Isolation and identification of 3: The biotransformation solution and the mycelia were extracted three times with
ethyl acetate. The organic phases were pooled, and concentrated under reduced pressure to obtain slurry. The slurry
was mixed with silica gel to homogeneity, dried completely, and then subjected to column chromatography. Gradient
elution was performed with dichloromethane–methanol (100:1; 50:1; 25:1) at 2 mL/min to obtain 3. The structure of 3
was identified by MS, 1H NMR, 13C NMR, DEPT135, and 1H–1H NOESY spectroscopy. Compound 3 was
30
crystallized from methanol; ½aꢁD ꢂ47 (c 0.11, CH3OH), 1H NMR (500 MHz, CDCl3): d 6.18 (d, 1H, J = 10 Hz), 6.09
(d, 1H, J = 10 Hz), 5.77 (s, 1H), 4.18 (dd, 1H, J = 10, 20 Hz), 4.18–4.13 (m, 1H), 3.49 (s, 1H), 2.70–2.52 (m, 4H),
2.43–2.30 (m, 3H), 2.18–2.00 (m, 1H), 1.98–1.90 (m, 3H), 1.59–1.56 (m, 1H), 1.48–1.42 (m, 3H), 1.22 (s, 3H), 0.88 (s,
3H). ESI-MS (m/z): 373.9 [M+H]+, 395.9 [M+Na]+.
2. Results and discussion
Compound 1 was biotransformed into 2 using A. ochraceus SIT34205 with 3 produced during the middle and late
stages of the biotransformation. The results of the TLC analysis of the sample after microbial transformation indicated
a small amounts of 1 with Rf = 0.73, 2 with Rf = 0.20, and 3 with Rf = 0.09 (data not shown). Therefore, the polarity of
3 was greater than that of 2 (Fig. 1).
The molecular weight of 2 was 356 [9], and that of 3 was m/z 373.9 in the ESI-MS result which appeared as a
[M+H]+ ion peak (Figure not shown), indicating that 3 had an additional hydroxyl group relative to 2. Thus, 3 was
speculated to be a dihydroxycanrenone. Compound 3 was structurally characterized using NMR (1H, 13C NMR,
DEPT135 and NOESY) according to the methods described previously [10,11].
The 1H NMR data of 3 revealed many similarities with those of 2 (Table not shown). The major differences were as
follows. For chemical shifts d 3.49, d 4.17, and d 4.28 in the low-field region, the strong peak at d 3.49 disappeared after
deuterium oxide exchange, suggesting the presence of a reactive hydrogen atom. Moreover, as demonstrated by
mAU
mAU
1750
1500
1250
1000
750
500
250
0
2500
2000
1500
1000
500
0
0
1
2
3
4
5
6
0
2
4
6
8
10
min
Fig. 1. HPLC chromatogram of the biotransformation sample (left panel) and the purified compound 3 (right panel). In the left panel, the retention
time of 4.108, 4.379, and 6.779 min were correspond to compounds 3, 2 and 1, respectively.

S.F. Rong et al. / Chinese Chemical Letters 23 (2012) 313–316
315
Table 1
13C NMR data for compounds 2 and 3.
C at various positions
2a
3a
C-1
35.43
35.43
199.75
124.83
162.68
128.84
137.90
37.73
55.75
36.28
67.96
35.85
43.92
46.58
22.51
34.17
94.70
15.61
17.18
31.08
29.09
176.28
71.19
41.93
198.06
124.94
161.45
128.66
138.89
36.57
56.45
42.15
66.04
35.37
43.36
46.19
22.69
35.37
94.97
15.28
11.93
30.97
29.11
176.64
C-2
C-3
C-4
C-5
C-6
C-7
C-8
C-9
C-10
C-11
C-12
C-13
C-14
C-15
C-16
C-17
C-18
C-19
C-20
C-21
C-22
a
Data were obtained at 125 MHz in CDCl3 using TMS as internal standard (chemical shift d (ppm)).
integration, the number of hydrogen atom corresponding to either of the chemical shifts was one, suggesting the
presence of oxygen atoms individually bonded to a methenyl group. Therefore, compound 3 can be identified as a
dihydroxyl compound.
The 13C NMR and DEPT135 spectra of 3 (Table 1) revealed that one molecule of 3 contains two methyl groups, six
methylene groups, eight methenyl groups, and six quaternary carbon atoms. The chemical shifts of the carbon atoms
in 3 were essentially similar to those of 2 except for the following differences. The chemical shift of C1 in 2 was at
d 35.43, and this signal was absent in the carbon spectrum of 3. An additional peak appeared at d 71.19. The chemical
shifts of both C2 and C10 were moved to the low field, with the values of d 41.93 and d 42.15, respectively. These data
infer that the hydroxyl group is at C1 position. Considering the NOESY spectra results, H-18 and H-19 were correlated
with H-11, but not with H-1. The correlation of H-1 with H-9 indicated that the two hydrogen atoms were sterically
close and can be considered to be on the same side [12]. H-9 was at a position, and thus H-1 may be at the a position
of C1, suggesting that the hydroxyl group might be at b position of C1. In the structural identification of
12b-hydroxymexrenone by Preisig et al. [10], the chemical shift of the adjacent C18 of the compound moved from
d 15.39 to d 8.54 in comparison with the carbon spectrum of mexrenone. In our study, the chemical shift of C19 of the
isolated 3 moved to the high-field, that is, from d 17.18 to d 11.93, compared with the carbon spectrum of 2, which
served as further evidence for the above deduction that the hydroxyl group at C1 position is in b configuration.
According to the above analysis, we conclude that 3 is 1b, 11a-dihydroxycanrenone, which is absent in the Reaxys
and CA databases (Fig. 2).
Previous studies [10] have shown that 1 may be hydroxylated by microorganisms at positions C2, C7, C9, C11,
C14, C15, and C16. In the microbial transformation of steroids by Hu et al. [13], steroids were hydroxylated by
microorganisms to several different hydroxysteroids, which indicated the presence of a series of hydroxylases in the
cytochrome P450 enzymes. In our study, canrenone was converted to the major product 2 and byproduct 3 by A.
ochraceus SIT34205. Different steroids focused on hydroxylation at different positions by A. ochraceus have been
reported. Progesterone was hydroxylated to 11a-hydroxyprogesterone and byproduct 6b,11a-dihydroxyprogester –
one by A. ochraceus TS [14]. Compound 1 was mainly hydroxylated to 15a-hydroxycanrenone by A. ochraceus AS3.
3930 [15]. These results are consistent with the previous reports [16], which revealed that the transformation pattern of
steroids can be influenced by substrate structure. Additionally, the result of structural identification indicates that

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S.F. Rong et al. / Chinese Chemical Letters 23 (2012) 313–316
O
O
O
HO
O
O
HO
OH
O
H
H
a
H
H
H
H
H
H
H
O
O
O
1
2
3
Fig. 2. Schematic of biotransformation of canrenone: (a) A. ochraceus SIT34205.
compound 3 is the product of further hydroxylation of 2. The purification of 11a-hydroxylase and 1b-hydroxylase
requires further investigation to inhibit the formation of 3.
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