Δ1-dehydrogenation and C20 reduction of cortisone and hydrocortisone catalyzed by rhodococcus strains

Article abstract of DOI:10.3390/molecules25092192

Prednisone and prednisolone are steroids widely used as anti-inflammatory drugs. Development of the pharmaceutical industry is currently aimed at introducing biotechnological processes and replacing multiple-stage chemical syntheses. In this work we evaluated the ability of bacteria belonging to the Rhodococcus genus to biotransform substrates, such as cortisone and hydrocortisone, to obtain prednisone and prednisolone, respectively. These products are of great interest from a pharmaceutical point of view as they have higher anti-inflammatory activity than the starting substrates. After an initial lab-scale screening of 13 Rhodococcus strains, to select the highest producers of prednisone and prednisolone, we reported the 200 ml-batch scale-up to test the process efficiency and productivity of the most promising Rhodococcus strains. R. ruber, R. globerulus and R. coprophilus gave the Δ1-dehydrogenation products of cortisone and hydrocortisone (prednisone and prednisolone) in variable amounts. In these biotransformations, the formation of products with the reduced carbonyl group in position C₂₀ of the lateral chain of the steroid nucleus was also observed (i.e., 20β-hydroxy-prednisone and 20β-hydroxy-prednisolone). The yields, the absence of collateral products, and in some cases the absence of starting products allow us to say that cortisone and hydrocortisone are partly degraded.

Full text of DOI:10.3390/molecules25092192

Article
Δ1-Dehydrogenation and C20 Reduction of Cortisone
and Hydrocortisone Catalyzed by Rhodococcus
Strains
Stefania Costa 1,*, Federico Zappaterra 1, Daniela Summa 2, Bruno Semeraro 2
and Giancarlo Fantin 3
1
Department of Life Sciences and Biotechnology, University of Ferrara, Via L. Borsari, 46, 44121 Ferrara,
Italy; federico.zappaterra@unife.it
2
GATE SRL, Via L. Borsari, 46, 44121 Ferrara, Italy; daniela.summa@unife.it (D.S.);
bsemeraro@gategreen.it (B.S.)
3
Department of Chemical and Pharmaceutical Sciences, University of Ferrara, Via L. Borsari, 46,
44121 Ferrara, Italy; giancarlo.fantin@unife.it
* Correspondence: stefania.costa@unife.it; Tel.: +39-0532-455-708
Received: 26 March 2020; Accepted: 4 May 2020; Published: 7 May 2020
Abstract: Prednisone and prednisolone are steroids widely used as anti-inflammatory drugs.
Development of the pharmaceutical industry is currently aimed at introducing biotechnological
processes and replacing multiple-stage chemical syntheses. In this work we evaluated the ability of
bacteria belonging to the Rhodococcus genus to biotransform substrates, such as cortisone and
hydrocortisone, to obtain prednisone and prednisolone, respectively. These products are of great
interest from a pharmaceutical point of view as they have higher anti-inflammatory activity than
the starting substrates. After an initial lab-scale screening of 13 Rhodococcus strains, to select the
highest producers of prednisone and prednisolone, we reported the 200 ml-batch scale-up to test
the process efficiency and productivity of the most promising Rhodococcus strains. R. ruber, R.
globerulus and R. coprophilus gave the Δ1-dehydrogenation products of cortisone and hydrocortisone
(prednisone and prednisolone) in variable amounts. In these biotransformations, the formation of
products with the reduced carbonyl group in position C20 of the lateral chain of the steroid nucleus
was also observed (i.e., 20β-hydroxy-prednisone and 20β-hydroxy-prednisolone). The yields, the
absence of collateral products, and in some cases the absence of starting products allow us to say
that cortisone and hydrocortisone are partly degraded.
Keywords: cortisone; hydrocortisone; biotransformations; prednisone; prednisolone; 20β-hydroxy-
prednisone; 20β-hydroxy-prednisolone; Rhodococcus spp.
1. Introduction
Steroids are lipids belonging to the terpenes class, and from a chemical-structural point of view
they contain a tetracyclic system of carbon atoms (cyclopentanoperhydrophenanthrene). This type of
compound is widespread in nature: thousands of steroids have been identified in living systems.
Over 250 sterols and related compounds have been reported to occur in plants (e.g., phytosterols,
diosgenin, and brassinosteroids), insects (e.g., ecdysteroids), vertebrates (e.g., cholesterol;
corticosteroids: glucocorticoids, mineralocorticoids; sex hormones: androgens, estrogens; bile acids,
vitamin D; and neurosteroids), and lower eukaryotes: yeasts and fungi (e.g., ergosterol and
ergosteroids) [1–3].
Molecules 2020, 25, 2192; doi:10.3390/molecules25092192
www.mdpi.com/journal/molecules

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Steroid-based drugs present a broad range of therapeutic applications and represent the highest
marketed category of pharmaceuticals, after antibiotics, with an annual production of more than one
million tons. Currently, about 300 steroid drugs are known, and this number tends to grow. Their
production represents the second category in the pharmaceutical market after antibiotics [4].
A large number of steroids are used as anti-inflammatory agents, immunosuppressants,
progestational agents, diuretics, anabolics, and contraceptives [5–7]. Some steroid compounds are
used for the treatment of prostate and breast cancer [8], as replacement therapy in patients with
primary or secondary adrenal insufficiency, as adrenal suppression therapy in congenital adrenal
hyperplasia and glucocorticoid resistance for adrenal insufficiency [9], for the prevention of heart
disease [10], as antifungal agents [11], and as active ingredients useful for the treatment of obesity
[12] and AIDS [13]. Recently, the antiviral activity against the herpes simplex virus type I of some
steroid glycosides was determined [14].
The structure of steroids is closely related to their biological activity, i.e., the type, number, and
regio and stereo position of the functional groups attached to the steroid core and the oxidation state
of the rings. For example, the presence of an oxygen-containing functional group at C11β is crucial for
inflammatory activity, the hydroxyl group linked to C17β determines the androgenic properties, the
aromatization of ring A results in estrogenic effects, and the corticoids have a 3-oxo-5-ene moiety and
the pregnane side chain at C17 [5,15].
In this field, corticosteroids are a group of hormones, produced by the adrenal gland cortex,
belonging to the steroid class. They are used for their anti-inflammatory and immunosuppressive
properties and for their effects on metabolism. They are divided into glucocorticoids, which control
the metabolism of carbohydrates, lipids, and proteins, and mineralcorticoids, which control the
electrolyte levels and the amount of water present in the blood.
Cortisone and cortisol (hydrocortisone) belong to the glucocorticoid class. They are
characterized by the presence of a ketone group in position C3, a double bond in position C4, and a
chain COCH2OH in C17, and they differ from each other by the fact that in the C11 position cortisone
has a carbonyl group while in the structure of hydrocortisone there is a hydroxyl group (Figure 1).
Figure 1. Chemical structures of cortisone and hydrocortisone.
Cortisone and hydrocortisone have a well-known anti-inflammatory activity, and it is equally
known that the presence of additional/second double bond at the C1-C2 position in prednisone and
prednisolone increases the mentioned activity: in particular Δ1-hydrocortisone (prednisolone) acetate
is four times more active than hydrocortisone acetate [16].
Therapeutic effects of steroids can often parallel undesirable side effects, especially when high
doses and long-term therapy are required. For this reason the use of more powerful drugs, such as
prednisone and prednisolone, can reduce these effects as a lower dose of drug is administered to
obtain the same therapeutic effect; prednisone and prednisolone have in fact proved to be four to five
times more active than cortisone and hydrocortisone [17].
The synthesis of prednisone and prednisolone by chemical methods requires various reaction
steps, in particular regarding prednisone as there are various ways of synthesizing it. In one of these,
it is synthesized from dihydrocortisone acetate. In the given example, this compound undergoes
dibromination by molecular bromine, giving a 2,4-dibromo derivative of dihydrocortisone.
Dehydrobromination with 3,5-lutidine, followed by subsequent hydrolysis of the acetyl group using
potassium bicarbonate, gives prednisone [18] (Figure 2).

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Figure 2. Synthesis of prednisone starting from dihydrocortisone acetate.
As for the chemical synthesis of prednisolone, one of various strategies starts from 21-acetoxy-
11β,17α-dihydroxy-5α-pregnan-3,20-dione, which undergoes dibromination by molecular bromine
in acetic acid at positions C2 and C4, and then the resulting dibromide is dehydrobrominated by
heating it in collidine, which gives prednisolone as an acetate at position C21. Hydrolyzing this
compound leads to the formation of prednisolone [18] (Figure 3).
Figure 3. Synthesis of prednisolone starting from 21-acetoxy-11β,17α-dihydroxy-5α-pregnan-3,20-dione.
In order to overcome all the problems deriving from chemical synthesis, the potential of
microbial steroid biotransformation has been known for several decades, as its application offers a
number of advantages over chemical synthesis. These advantages concern (i) the regio- and/or
stereospecific functionalization of molecules at positions not always available for chemical agents, (ii)
how multiple consecutive reactions are carried out in a single operation step, and (iii) more
ecofriendly processes (i.e., mild reaction conditions and aqueousmedia), as several studies have been
conducted on the biotransformations of steroid compounds [19].
Recently the biotransformation of cortisone acetate and hydrocortisone acetate with Arthrobacter
simplex (Pimelobacter simplex) to the corresponding prednisone acetate [20–22] and prednisolone
acetate [23] has been reported. Moreover, prednisolone is also obtained from hydrocortisone by
biotransformation with Arthrobacter simplex [24] using recombinant 3-ketosteroid-Δ1-
dehydrogenases [25] and as a hydrocortisone biometabolite from unicellular microalgal cultures [26].
Furthermore, recently the 11β-reduction of prednisone by biotransformation capacities were
confirmed to produce prednisolone [27].
On the other hand, biotransformations are widely used to obtain new steroidal derivatives that
can have some therapeutic advantages, such as higher activity, longer half-life, and reduced side
effects. In this field, various microorganisms afford the 20β-hydroxy-prednisone from prednisone
[28] and 20β-hydroxy-prednisolone from prednisolone [29,30].
The Actinobacteria have been widely studied and their biotransformation capacities confirmed in
various types of transformations of steroid rings, such as the reduction of the C-C and C-O double
bonds, oxidation of the hydroxyl (OH) group, dehydrogenation and hydroxylation, and in many
cases also in the lateral-chain degradation processes or the total degradation of the steroid ring [31].
Rhodococci belong to the order of Actinomycetales, they are gram-positive, obligate aerobic, non-
mobile, and non-sporulating bacteria that are usually found in soil and aquatic environments and are
considered very important as they can be used industrially [32]. Several studies have shown that the

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species belonging to this genus are able to grow both in mesophilic conditions [33] and in
psychrophilic conditions [34].
In particular, Rhodococcus include aerobic bacterial species important for their ability to
biotransform a wide range of steroids via hydroxylation or Bayer–Villiger oxidation, while the
Corynebacterium and Nocardia genera are known to provide dehydrogenation products [31].
Moreover, in previous works the biotransformations of various bile acids with Rhodococcus spp.
have been reported and Δ1-dehydrogenation, the partial degradation of the C17-side chain together
with new 9,10-secosteroids derivatives, has been achieved [35,36]. The highlighted ability of these
microorganisms to hydroxylate and dehydrogenate the steroid ring system prompted us to test the
capabilities of various Rhodococcus strains towards the biotransformation of cortisone and
hydrocortisone.
The purpose of this work is to evaluate the biotransformative capacity of some bacteria
belonging to the Rhodococcus genus using cortisone and hydrocortisone as substrates with the aim of
isolating products with greater therapeutic activity than the starting compounds. In this study we
present the results of a preliminary screening followed by the isolation and characterization of the
products obtained from batch cultures of the microorganisms that tested positive for the screening
(strains with capacity to transform the cortisone and/or hydrocortisone).
After an initial lab-scale screening where 13 representatives of the Rhodococcus genus were tested
towards the biotransformation of cortisone and hydrocortisone, preparative cultures of the strains
that were found to be positive to verify the biotransformation of the products and their yields were
set up.
2. Results and Discussion
2.1. Rhodococcus Screening and Selection
Due to the numerous harmful and dangerous effects of the reagents used in the chemical
synthesis of prednisone and prednisolone, research is increasingly turning towards greener
approaches. The use of bromine in the chemical synthesis can cause an explosive risk as well as
irritating and respiratory effects if you come into contact with this reagent, also as regards 3,5-lutidine
there are particular risks as it is flammable corrosive and toxic. To overcome all these problems, the
biotransformative approach using non-pathogenic microorganisms has proved to be of great interest
for the mild reaction conditions and the water-based culture medium of the microorganisms. In
previous studies it has been shown that there is much evidence of the capacity of Rhodococcus strains
to biotransform steroidal substrates to have Δ1-dehydrogenation products. [35,36]. Starting from
these results, 13 Rhodococcus strains in the biotransformations of cortisone and hydrocortisone were
tested. Screening tests were carried out in order to select microrganisms able to biotransformate these
substrates. In Table 1 results of this screening are reported with the relative retention factors (Rf) of
the product obtained.

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Table 1. Analitical results of Rhodococcus screening in biotransformation of cortisone and hydrocortisone.
Bacteria
Products from Cortisone Products from Hydrocortisone
R. zopfii
Degradation
no product
no product
Rf 0.23, 0.55
Rf 0.55
Rf 0.45
no product
no product
Rf 0.21
R. opacus
R. fascians
R. baikonurensis
R. globerulus
Rf 0.45
R. aetherivorans
R. coprophilus
Rf 0.55
no product
Rf 0.45
Rf 0.55
R. rhodochrous NCIMB 11216
Rhodococcus sp. R312
R. equi
no product
no product
no product
Rf 0.55
no product
no product
no product
Rf 0.45
R. ruber
R. rhodochrous DSM 43273
R. erythropholis
Rf 0.55
degradation
Rf 0.45, 0.21
Rf 0.23, 0.55
Some of the tested bacteria were able to biotransform the administered substrates in particular,
regarding the biotransformations of cortisone, R. globerulus, R. aetherivorans, R. coprophilus, R. ruber,
and R. rhodochrous DSM 43273 converted the starting substrate into a product having Rf equal to 0.55.
The reactions conducted with R. erythropholis and R. baikonurensis, in addition to the product just
mentioned, generated another compound with an Rf of 0.23.
Biotransformation activity has not been verified with R. opacus, R. fascians, Rhodococcus sp. R312,
R. rhodochrous NCIMB 11216, and R. equi.
In the biotransformation of cortisone R. zopfii exhibited a particular behavior leading to a
complete degradation of the substrate without providing biotransformation products. In this regard,
it is known that some microorganisms are able to use steroids as a carbon source, degrading the
lateral chain and subsequently the steroid nucleus, reaching complete mineralization [36].
Figure 4 shows the probable degradation pathway of cortisone by Actinobacteria [31] based on
the literature data.
Figure 4. Metabolic pathway of steroid degradation.
Steroids with 3-oxo-4-ene structure, such as cortisone and hydrocortisone, are subjected to the
cleavage of ring B. The Δ1-dehydrogenation of cortisone to give prednisone is the initial stage that
leads to the complete elimination of the C17 chain with the ADD (androstadienedione) formation. This

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is a classic step in the degradation of other steroids, such as sitosterols, testosterone, and bile acids
[37].
ADD is subjected to hydroxylation at the C9-position catalyzed by 3-ketosteroid-9α-hydroxylase
(KSH), a two-component iron-sulfur-containing monooxygenase [38–40]. This reaction leads to the
spontaneous cleavage of the ring B by a retro-aldol cleavage and the formation of the aromatic 9,10-
secosteroids, which undergo further degradation [41].
Because of this knowledge we can, therefore, assume that the Δ1-dehydrogenation is the initial
stage that leads to the degradation of the C17-chain and to the opening of the ring B and subsequently
to the total degradation of cortisone. Furthermore non-quantitative yields and the absence of
collateral products and starting product confirm this assumption.
As for the biotransformations of hydrocortisone, in most cases a single product with an Rf of
0.45 was obtained, only in one case with R. baikonurensis a compound with an Rf of 0.21 was detected,
while R. erythropholis was the only microorganism able to produce two compounds (Rf 0.45 and 0.21).
R. rhodochrous DSM 43273 had completely metabolized the starting substrate without providing
detectable products through thin-layer chromatography (TLC) analysis. Most likely, R. rhodochrous
DSM 43273 completely degraded the carbon source following a metabolic pathway similar to that of
cortisone as previously described. Finally, R. opacus, R. fascians, R. aetherivorans, R. rhodochrous NCIMB
11216, Rhodococcus sp. R312, and R. equi showed no biotransformative capacity towards
hydrocortisone.
2.2. Characterization of the Biotransformation Products of Cortisone
Semi-preparative cultures were necessary to isolate and identify the biotransformation products.
The identification of the products was carried out by NMR analysis, comparing the signals obtained
with those of the spectra present in the literature. In general, from the biotransformation of cortisone
with Rhodococcus species, two products were obtained: prednisone and 20β-hydroxy-prednisone, the
first being the product of the dehydrogenation of the C1-C2 bond in cortisone, while 20β-hydroxy-
prednisone in addition to Δ1-dehydrogenation presents the reduction of the carbonyl group in the
position C20β as shown in Figure 5.
Figure 5. Products obtained from biotransformation of cortisone with Rhodococcus spp.
Table 2 shows the products of the biotransformations of cortisone with the relative yields and
reaction times; the quantity of residual cortisone is also specified. The biotransformation yields were
obtained by working out the percentage of the ratio between the moles of the product obtained
compared to the moles of the administered substrate. The relative standard deviation value for
statistical analysis was also reported.

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Table 2. Biotransformations of cortisone with Rhodococcus spp.
Time of
Biotransformation
(h)
20β-Hydroxy-
Prednisone
(% yield)
Cortisone
Prednisone
(% yield)
Bacteria
Residue
(%)
27 ± 3
(0.053 ± 0.005 g )
33 ± 6
68 ± 4
R. baikonurensis
R. globerulus
R. aetherivorans
R. coprophilus
R. ruber
72
72
72
24
72
72
72
--
(0.134 ± 0.007 g)
65 ± 3
--
--
--
--
(0.065 ± 0.012 g)
35 ± 3
(0.129 ± 0.006 g)
63 ± 7
(0.069 ± 0.006 g)
94 ± 2
(0.125 ± 0.014 g)
--
(0.185 ± 0.004 g)
52 ± 4
47 ± 4
(0.093 ± 0.008 g)
53 ± 3
(0.102 ± 0.008 g)
31 ± 3
R. rhodochrous DSM
43273
(0.0065 ± 0.006)
33 ± 5
(0.105 ± 0.006)
28 ± 6
37 ± 6
R. erythropolis
(0.065 ± 0.01 g)
(0.073 ± 0.011 g)
(0.056 ± 0.012 g)
The product of Δ1-dehydrogenation (prednisone) was the only one obtained from the
biotransformations with R. globerulus, R. aetherivorans, R. coprophilus, R. ruber, and R. rhodochrous DSM
43273. Among these bacteria, only in one case (R. coprophilus after 24 h of biotransformation), was no
residual cortisone observed, and the yield was very high (94%). This result clearly underlines this
strategy as a valid alternative to the chemical synthesis of prednisone, since the time of
biotransformation is rather short when whole cells are rather short, and the yield of the product is
almost quantitative. Regarding the biotransformations of cortisone with R. globerulus, R. aetherivorans,
and R. ruber after 72 h of incubation with the substrate, yields of prednisone production were quite
similar: 33% with R. globerulus, and 35% and 52% with R. aetherivorans and R. ruber, respectively. In
1
these cases, variable amounts of cortisone residue were observed (47–65%). The H- and 13C-NMR
spectra showed the characteristic signals of the C1-C2 double bond at 6.19 (C2-H), 7.63 (C1-H), 127.7
(C2), and 158.4 (C1) ppm of prednisone. On the other hand, in biotransformations carried out with R.
baikonurensis and R. erythropolis, after 72 h of reaction, in addition to prednisone with yields of 27%
and 33% respectively, both bacteria produced a new compound corresponding to 20β-hydroxy-
prednisone (yield 68% for R. baikonurensis and 37% for R. erythropolis). The stereochemistry of the C20-
1
reduction is confirmed by comparing the H-NMR data (i.e., 4.61 (C20-H) and 4.52 (C21-H) ppm in
C5D5N) and 13C-NMR data (i.e., 65.0 (C21) and 72.5 (C20) ppm) with data recorded for the commercially
available compound. This product could be an interesting derivative of the bioactive prednisone.
2.3. Characterization of the Biotransformation Products of Hydrocortisone
As in the biotransformation of cortisone, in the case of hydrocortisone two types of compound
were also obtained: prednisolone, deriving from the Δ1-dehydrogenation of the ring A, and 20β-
hydroxy-prednisolone, which is a product of the reduction of the carbonyl group in the side chain
(C20) as shown in Figure 6.
Figure 6. Products obtained from biotransformation of hydrocortisone with Rhodococcus spp.

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The products obtained from the biotransformations of hydrocortisone with their relative yields
and reaction times are reported in Table 3, and the quantities of residual hydrocortisone are also
reported (where present). Yield percentages of biotrasformation have been calculated on the basis of
the weights of the products obtained after chromatography separation. The relative standard
deviation value for statistical analysis was also reported.
Table 3. Biotransformations of hydrocortisone with Rhodococcus spp.
Time of
Biotransformation
(h)
20β-Hydroxy-
Prednisolone
(% yield)
Hydrocortisone
Residue
Prednisolone
(% yield)
Bacteria
(%)
R.
32 ± 3
72
72
24
72
72
--
--
baikonurensis
(0.063 ± 0.006 g)
76 ± 2
(0.151 ± 0.004 g)
97 ± 2
23 ± 1
R. globerulus
R. coprophilus
R. ruber
--
--
--
(0.045 ± 0.002 g)
--
(0.192 ± 0.004 g)
56 ± 4
40 ± 4
(0.111 ± 0.009 g)
37 ± 5
(0.072 ± 0.007 g)
18 ± 6
40 ± 8
R. erythropolis
(0.073 ± 0.01 g)
(0.079 ± 0.016 g)
(0.035 ± 0.012 g)
R. coprophilus is the only microrganism able to bioconvert hydrocortisone after 24 h in
prednisolone with a yield equal to 97% without the presence of residual hydrocortisone; the 1H and
13C-NMR spectra show the characteristic signals 6.27 (C2-H), 7.24 (C1-H), 127.1 (C2) and 156.8 (C1) ppm
of prednisolone. R. globerulus and R. ruber afforded the same product after 72 h of reaction with
different yields (76% and 56%, respectively), but in these cases a certain amount of residual
hydrocortisone was observed.
R. baikonurensis transformed hydrocortisone into 20β-hydroxy-prednisolone without recovering
hydrocortisone. The stereochemistry of the C20-reduction is supported by the comparison of the
recorded NMR data with the data given in the literature [29]: 3.85 (C20-H), 3.91 (C21-H), 65.3 (C21), and
79.1 (C20) ppm. The yield after 72 h of biotransformation is quite low (32%), and a possible explanation
may be that the enzymes of the microorganism are able to form 20β-hydroxy-prednisolone and
subsequently the substrate is metabolized via the steroid degradation pathway described previously.
This process includes the initial oxidation of the ring A, degradation of the side chain, and finally
complete mineralization.
Finally, R. erythropolis provided both the prednisolone and the 20β-hydroxy-prednisolone
biotransformation products with yields of 37% and 40%, respectively, after a 72-hour-reaction. In this
case, even using the maximum biotransformation time, 18% of residual hydrocortisone was
recovered.
3. Materials and Methods
3.1. Chemicals and Rhodococcus Strains
Cortisone and hydrocortisone were purchased from Merck KGaA (Darmstadt, Germany), and
20β-hydroxy-prednisone was purchased from Toronto Research Chemical Inc. (Toronto, Canada).
Plate count broth (PCB) is commercially available from Oxoid (Basingstoke, UK) and contains
tryptone enzymatic digest from casein 5 g/L, yeast extract 2.5 g/L, and glucose 1 g/L. All the other
chemicals were purchased from Fluka Analytical (Steinheim, Germany) unless otherwise stated.
The 13 Rhodococcus strains belong to the collection of microorganisms of the Life Sciences and
Biotechnology Department of the University of Ferrara and they were purchased from the DSMZ
(Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures GmbH) company
(Table 4). The master cell bank of every strain was maintained at −20 °C in cryovials in Plate count

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broth medium (1 mL) mixed with glycerol (0.5 mL) as a crioprotectant agent. The working cell bank
was conserved at 4 °C in plate count agar (PCA) slants for 6 months and used for seed cultures.
Table 4. Rhodococcus strains used for biotransformation screening of cortisone and hydrocortisone.
#
1
Genus
Species
zopfii
Identification Code
DSM 44108
DSM 43250
DSM 43985
DSM 44587
DSM 43954
DSM 44752
DSM 43347
NCIMB 11216
CBS 717.73
IFO 3730
Rhodococcus
Rhodococcus
Rhodococcus
Rhodococcus
Rhodococcus
Rhodococcus
Rhodococcus
Rhodococcus
Rhodococcus
Rhodococcus
Rhodococcus
Rhodococcus
Rhodococcus
2
opacus
3
fascians
4
baikonurensis
globerulus
aetherivorans
coprophilus
rhodochrous
sp. R312
equi
5
6
7
8
9
10
11
12
13
ruber
DSM 6264
rhodochrous
erythropholis
DSM 43273
DSM 43188
3.2. Rhodococcus Biotransformation Screening Conditions
For each of the selected Rhodococcus strains, a loopful of bacterial cells cultured on the plate count
agar was transferred to 50 mL Erlenmeyer flasks containing 10 mL of sterile PCB medium and
incubated at 30 °C and 110 rpm in an orbital shaker for 48 h. Each microorganism was inoculated in
three Erlenmeyer flasks, closed with cotton plugs, and submitted to the same protocol.
After the bacteria were grown, a solution of the substrate (cortisone or hydrocortisone) in
dimethylsulfoxide (DMSO) (0.1 mL containing 10 mg of substrate) was added. The course of the
reactions was followed by withdrawing samples (1 mL) every 24 h up to 72 h from the administration
of the substrate. The reactions were stopped after 72 h, as no significant differences were observed
between the results of the TLC analysis performed at 48 h and 72 h. Samples were then centrifuged
(6720 RCF; 10 min) in order to remove the cells, and the supernatants were extracted with ethyl
acetate and immediately analyzed by TLC on silica gel using ethyl acetate as an eluent.
3.3. Semi-Preparative Biotransformation Protocol
The biotransformations showing additional spots other than the starting material were repeated
on a semipreparative scale (200 mL) in order to isolate the products. For each of the selected
Rhodococcus strains, a loopful of bacterial cells cultured on PCA was transferred to 50 mL Erlenmeyer
flasks containing 20 mL of sterile PCB medium and incubated at 30 °C and 110 rpm in an orbital
shaker for 48 h. The whole culture was introduced into a 500 mL Erlenmeyer flask containing 200 mL
of sterile PCB, and after 48 h incubation at 30 °C and 110 rpm, the substrate (0.2 g) in DMSO (2 mL)
was added and the culture was maintained in the same conditions for a maximum of 72 h. All tests
were carried out in triplicate for statistical significance. A blank sample was also incubated containing
all the reagents but no bacteria. The reaction course was monitored by withdrawing samples (1 mL)
every 24 h up to 72 h of reaction, and the semipreparative reactions were followed by TLC analysis
and stopped when the higher conversion was reached. TLC analysis was performed using 1 ml of
sample taken every 24 h from the flask in which the reaction was conducted. The sample was
subsequently subjected to centrifugation, extraction with ethyl acetate, and immediately analyzed
using TLC on silica gel using ethyl acetate as an eluent, following the same protocol used in the
screening procedure.
The cells were removed by centrifugation (5242 RCF, 20 min) and the supernatant was extracted
with ethyl acetate (3 × 80 mL). The organic layer was dried over anhydrous Na2SO4, the solvent was
evaporated, and the crude mixture was purified on a chromatographic column (silica gel, ethyl
acetate/cyclohexane 50/50 as an eluent). The biotransformation yields were obtained by working out

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the percentage of the ratio between the moles of the product obtained compared to the moles of the
administered substrate.
3.4. Analitical Methods
TLC was performed on precoated silica gel plates (thickness 0.25 mm, Merck) and silica gel
(Fluka, Kiesegel 60, 70–230 mesh) was used for preparative column chromatography.
Melting points are uncorrected and were determined on a 510 Büchi melting point instrument.
1H and 13C NMR spectra were obtained with a Varian Gemini 300 spectrometer operating at 300 MHz
(1H) and 100 MHz (13C), with Me4Si as an internal standard.
3.5. Compound Data
17α,21-dihydroxy-1,4-pregnadiene-3,11,20-trione (prednisone): m.p. 234 °C; 1H-NMR (CDCl3): δ
0.67 (s, 3H, C18-CH3); 1.42 (s, 3H, C19-CH3); 1.69 (m, 1H, C7-H); 1.73 (m, 1H, C7-H); 1.92 (m 1H; C16-H);
1.94 (m, 2H, C15-H); 1.98 (m, 1 H, C8-H); 1.98 (m, 1H, C6-H); 2.01 (m, 1H, C6-H); 1.99 (d, 1H, J = 3.1, C9-
H); 2.06 (m, 1H, C14-H); 2.38 (m, 1H, C12-H); 2.72 (m 1H; C16-H); 2.77 (m, 1H, C12-H); 4.24 (d, 1H, J = 20
Hz, C21-H); 4.62 (d, 1H, J = 20 Hz, C21-H); 6.07 (t, 1H, J = 1.8 Hz, C4-H); 6.19 (dd, 1H, J = 10.2 and 1.8
Hz, C2-H); 7.63 (d, 1H, J = 10.2 Hz, C1-H); 13C-NMR (CDCl3): δ 16.2 (C18); 19.3 (C19); 24.1 (C15); 33.3 (C7);
34.9 (C6); 35.2 (C16); 37.4 (C8); 44.1 (C10); 50.8 (C14); 51.1 (C12); 52.3 (C13); 61.1 (C9); 67.8 (C21); 89.1 (C17);
124.7 (C4); 127.8 (C2); 158.2 (C1); 170.9 (C5); 188.6 (C3); 211.4 (C11); 212.7 (C20).
11α,17β,21-trihydroxy-1,4-pregnadiene-3,20-dione (prednisolone): m.p. 235 °C; 1H-NMR
(CDCl3): δ 0.97 (s, 3H, C18-CH3); 1.08 (d, 1H, C9-H); 1.10 (m, 1H, C7-H); 1.45 (s, 3H, C19-CH3); 1.45 (m,
1H, C15-H); 1.55 (m, 1H, C16-H); 1.56 (m, 1H, C12-H); 1.71 (m, 1H, C14-H); 1.72 (m, 1H, C15-H); 2.09 (m,
1H, C12-H); 2.13 (m, 1H, C7-H); 2.15 (m, 1H, C8-H); 2.35 (m, 1H, C6-H); 2.57 (m, 1H, C6-H); 2.71 (m, 1H,
C16-H); 4.28 (d, 2H, C21-H); 4.50 (s, 1H, C11-H); 6.02 (s, 1H, C4-H); 6.27 (d, 1H, C2-H); 7.24 (d, 1H, C1-
H); 13C-NMR (CDCl3): δ 16.9 (C18); 20.9 (C19); 23.8 (C15); 31.2 (C7); 31.8 (C6); 33.5 (C16); 34 (C8); 38.9 (C10);
44.1(C14); 47.1 (C12); 51.1 (C13); 55.4 (C9); 66.5 (C21); 68.9 (C11); 88.6 (C17); 121.8 (C4); 127.1 (C2); 156.8 (C1);
170.5 (C5); 185.8 (C3); 212.1 (C20).
17α,20β,21-trihydroxy-1,4-pregnadiene-3,11-dione (20β-hydroxy-prednisone): m.p.240–242 °C;
1H-NMR (CDCl3): δ 0.81 (s, 3H, C18-CH3); 1.03 (m, 1H, C15-H); 1.43 (s, 3H, C19-CH3); 1.50 (m, 1H, C7-
H); 1.77 (m, 1H, C6-H); 1.81 (m, 1H, C7-H); 1.82 (m, 1H, C15-H); 1.90 (m, 1H, C14-H); 1.92 (m, 1H, C6-
H); 1.93 (m, 1H, C8-H); 2.01 (m, 1H, C16-H); 2.45 (m, 1H, C9-H); 2.48 (m, 1H, C16-H); 2.52 (m, 1H, C12-
H); 2.56 (m, 1H, C12-H); 2.70 (m, 1H, C12-H); 3.76 (brs, 1H, C20-H) (4.61, m in C5D5N); 3.76 (brs, 1H, C21-
H) (4.52, m in C5D5N); 6.06 (t, 1H, J = 1.26, C4-H); 6.18 (dd, 1H, J = 10.3, 1.9, C2-H); 7.67 (d, 1H, J = 10.2,
C1-H); 13C-NMR (CDCl3): δ 15.9 (C18); 19.3 (C19); 24.5 (C15); 34.8 (C7); 35.0 (C6); 33.4 (C16); 37.7 (C8); 44.1
(C10); 49.5 (C14); 52.7 (C12); 52.8 (C13); 61.3 (C9); 65.0 (C21); 72.5 (C20); 85.0 (C17); 124.6 (C4); 127.7 (C2);
158.4 (C1); 171.2 (C5); 188.7 (C3); 213.3 (C11).
11β,17α,20β,21-tetrahydroxy-1,4-pregnadiene-3-one (20β-hydroxy-prednisolone): mp 185–187
°C; 1H-NMR (CDCl3): δ 1.06 (s, 3H, C18-CH3); 1.11 (m, 1H, C7-H); 1.12 (d, J = 10, 1H, C9-H); 1.44 (s, 3H,
C19-CH3); 1.52 (m, 1H, C15-H); 1.54 (m, 1H, C16-H); 1.6 (m, 1H, C12-H); 1.77 (m, 1H, C14-H); 1.8 (m, 1H,
C15-H); 2.07 (m, 1H, C12-H); 2.12 (m, 1H, C7-H); 2.18 (m, 1H, C8-H); 2.23 (m, 1H, C6-H); 2.35 (m, 1H, C6-
H); 2.45 (m, 1H, C16-H); 3.85 (m, 1H, C20-H); 3.91 (m, 2H, C21-H); 4.41 (s, 1H, C11-H); 6.02 (s, 1H, C4-H);
6.27 (dd, J = 10 and 1.5, 1H, C2-H); 7.29 (d, J = 10, 1H, C1-H); 13C-NMR (CDCl3): δ 16.39 (C18); 21.1 (C19);
23.2 (C15); 33.5 (C7); 31.9 (C6); 35.3 (C16); 33.2 (C8); 42.2 (C10); 55.1 (C14); 47.4 (C12); 46.9 (C13); 55.5 (C9);
65.3 (C21); 69.1 (C11); 79.1 (C20); 84.9 (C17); 120.9 (C4); 126.1 (C2); 159.2 (C1); 173.8 (C5); 187.8 (C3).
4. Conclusions
In this work the ability of some strains belonging to the Rhodococcus genus to biotransform
cortisone and hydrocortisone was tested. The aim of this work was to find new active compounds
and alternative methods to synthesize chemical products already known. To reach this goal, we
performed a screening of several Rhodococcus strains as it has been shown in the literature that they
have a high ability to biotransform many substances including steroids. Lab-scale experiments

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allowed us to identify the positive strains (strains with the capacity to transform the cortisone and/or
hydrocortisone), and subsequently, the preparation on a semi-preparative scale of the same allowed
for the characterization of the products obtained with the relative biotransformation yields. For both
substrates used, Δ1-dehydrogenation products (e.g., prednisone and prednisolone) were obtained, in
particular with R. coprophilus where the bioconversion yields were practically quantitative, making it
a good candidate for the synthesis of prednisone and prednisolone using a method that follows the
philosophy of green chemistry.
With regard to the reduction products at the level of the carbonyl group in C20, the
stereochemistry of the hydroxyl group was carried out by comparing NMR spectra of known
substances or commercial standards.
In these biotransformations, this type of product has been obtained with lower yields than those
previously described. If of interest, it could be useful to study the reaction conditions in order to
optimize the yield of generation of these compounds.
Author Contributions: Conceptualization and writing—review and editing S.C., investigation and analysis
F.Z., B.S. and D.S., supervision and project administration G.F. All authors have read and agreed to the published
version of the manuscript.
Funding: Ambrosialab: Ferrara, Italy (Grant 2019), Italian Ministry of Education University and Research (Grant
MIUR-PRIN 2017E84AA4_002).
Acknowledgments: The authors would like to acknowledge Dr. Elisa Durini and Elisa Buzzi for technical
assistance.
Conflicts of Interest: The authors declare no conflict of interest.
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