Crystal Engineering of Naturally Occurring Seselin to Obtain a Co

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Crystal Engineering of Naturally Occurring Seselin to Obtain a Co-crystal with Enhanced Antileishmanial Activity, Hirshfeld Surface Analysis and Computational Insight Ejaz Hussain, Rajesh Kumar, M. Iqbal Choudhary, and Sammer Yousuf Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b00602 • Publication Date (Web): 05 Jul 2018 Downloaded from http://pubs.acs.org on July 9, 2018

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Crystal Growth & Design

Crystal Engineering of Naturally Occurring Seselin to Obtain Co-crystal with Enhanced Antileishmanial Activity, Hirshfeld Surface Analysis and Computational Insight

Ejaz Hussain †, Rajesh Kumar †, M.Iqbal Choudhary †‡, SammerYousuf †*.

†

H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological

Sciences, University of Karachi, Karachi-75270, Pakistan. ‡

Department of Biochemistry, Faculty of Science, King Abdulaziz University, Jeddah-21412,

Saudi Arabia.

*Correspondence author: H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi-75270, Pakistan.

Tel: +92-21-34824924-5

Fax: +92-21-4819018-9

E-mail address: [email protected]

1 ACS Paragon Plus Environment

Crystal Growth & Design 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

ABSTRACT Seselin (8,8-dimethyl-2H,8Hbenzo[1,2-b:3,4-b']dipyran-2-one) is a naturally occurring pyrano coumarin, isolated from Seseli diffusum (Roxb. ex Sm.) Sant. & Wagh.We have synthesized cocrystal of seselin with thiourea by using liquid-assisted grinding and solution methods (via refluxing). The purity and homogeneity of seselin-thiourea (1:1) co-crystal was confirmed by analysis based on single-crystal X-ray diffraction technique. A deep insight into the geometry of co-crystal demonstrated that 1:1 co-crystal stoichiometry is sustained by N-H…O hydrogen bonding between amine (-NH2) groups of thiourea and carbonyl group of seselin. Synthesized co-crystal exhibited good anti-leishmanial activity invitro (IC50 = 13.2 + 1.2 µg/mL) in comparison to seselin (IC50 = 29.4 + 1.0 µg/mL) and thiourea (IC50 = 86.06+0.6µg/mL), against the tested standards, pentamidine (IC50 = 5.09 + 0.09 µg/mL) and amphotericin B (IC50 = 0.12 + 0.15µg/mL). Geometrical values of computationally optimized structure were calculated by density functional theory (DFT) at B3LYP/6-31(d,p) to obtain HOMOs and LUMOs of cocrystal, and found to be consistent with XRD data. Hence, this study further highlights the significance of co-crystallization towards improving the efficacy of medicinal and industrial materials. Furthermore, the consistency of computational results with crystallographic values


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ensured the computational modeling of co-crystal is equally important to predict the stable geometries, and next-generation applications of co-crystals. Key Words: Co-crystal, Seselin, Sesseli diffusium, Leishmaniasis, Single-crystal X-ray diffraction, Density functional theory (DFT), Hirshfeld surface analysis.

1. INTRODUCTION 2. Co-crystals represent a class of multi-component compounds having a significant effect on physiochemical and pharmaceutical properties1. The non-covalent interactions, predominantly hydrogen bonding2, halogen bonding3,4or heterosynthones5 (in supramolecularco-crystals) trigger the assembly of the components in a fixed stoichiometry at ambient conditions. Crystal engineering approaches via co-crystallization are mean to alter the physiochemical properties of active pharmaceutical ingredients (APIs) to enhance their stability, efficacy, and bioavailability6,7. In fact, co-crystallization is used extensively in industries to associate APIs with excipient (s) for designing effective drugs dosage forms. Their application ranges from drug designing to the analysis of active pharmaceutical ingredients (APIs)8. Co-crystals have significant difference in physiochemical and biological properties from their individual components. Indeed, the purpose of co-crystallization is to obtain superior physiochemical and biological properties from the existing APIs, while the original properties of APIs should sustaine9. In this context, numerous pharmaceutical key drugs were crystallized with suitable coformers to fine-tune the desired properties10,11. Many crystal engineering approaches as analytical techniques have been introduced for the development of co-crystals12. An antitumor pro-drug temozolmide (TZM) that has broad spectrum anti-neoplastic activity was co-crystallized

with

amide

coformers

(nicotineamide,

p-hydroxybenzamide,

pyrazinamide, saccharine, and caffeine) to obtain stable co-crystals in alkaline medium13. Nalidixic acid is a quinolone antibiotic used in the treatment of urinary tract infection. The co-crystals of nalidixic acid were developed to improve the bioavailability due to replacement of intermolecular drug-drug interaction in polymorph with strong drug3 ACS Paragon Plus Environment


coformer hydrogen bonds in co-crystals14. The limited in-vivo efficacy and poor bioavailability of quercetin was improved by co-crystallization with caffeine and isonicotinamide as conformers15. Along with their pharmaceutical importance, co-crystals are equally important for sensing applications. Co-crystal of 10-methylphenthiazine and 1,3-dinitrobenzene was adequately utilized for the optical sensing of TNT based explosives16. Micro- and nano-crystalline co-crystals exhibit single-crystal-to-singlecrystal chemical reactivity that is promising for sensors, and high-density data storage devices17. Currently co-crystallization is now a preferred technique to improve dissolution, solubility, and bioavailability of less water-soluble drugs18-20. Carbamazepine co-crystals with nicotinamide (NCT), malonic acid (MLN), glutaric acid (GTA), saccharin (SAC), anhydrous oxalic acid (OXA), succinic acid (SUC), and salicylic acid (SLC) exhibit

152 times greater solubility than the stable carbamazepine dihydride form21. Hence, the co-crystallization has been an adequate subject for the researchers from many past years because of their use in many industries which includes pharmaceuticals, paper, textile, photographic, chemical processing, and electronics22. There are many commercially important compounds that can be co-crystallized with suitable coformers to fine-tune the stable, and superior properties for next-generation applications. The US-FDA approval for co-crystals to be considered as drug intermediates has opened new vistas, both in pharmaceutical and academic research sector. The article entitled, “Reflection paper” by the European medicines agency has discussed in detail the regularity implementation of the co-crystals and clearly mention that any co-crystal will not be consider as a new drug if its safety and efficacy found to be equivalent to the active pharmaceutical ingredient of the considered co-crystal23. The parasitic infection leishmaniasis is transmitted through bite of infected sand fly (Phlebotomus or Lutzomyia). The infection is responsible for more than 2 million new cases, and 70,000 deaths annually along with 350 million people at risk in various regions of world, predominantly in 89 countries of American, Asian, and African subcontinents, and Mediterranean region24. The severity of infection depends upon the type and the penetrating ability of the parasite ranging from facial and cutaneous to subcutaneous and the most severe visceral leishmaniasis25. According to a worldwide survey of the WHO to identify the world-wide regions with distribution and major burdens of various types of 4 ACS Paragon Plus Environment

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leishmaniasis in 102 countries, Pakistan has identified among those having high burden of both cutaneous and viral leishmaniasis (World Health Organization: Weekly Epidemiological Record (WER). 2016). Antimonial drugs are the most effective and remain the only primary treatment in various effected regions of world, followed by amphotericin B, and pentamidine as second line of treatment 26. However, the severe side effects and development of drug resistance due to complex immune response of the causative agents open new vistas for the search of alternatives. That has been resulted in identification and approval of miltefosine as the only oral treatment for leishmaniasis27. The low efficacy, high price and increased drug resistance developed in last 10 to 20 years against amphotericin B, pentamidine not only increasing the economic burden but also demand a vigorous search towards more effective treatment from available resources including locally available natural products, and through repurposing of existing drugs. Seselin

(8,8-dimethyl-2H,8H

benzo[1,2-b:3,4-b']dipyran-2-one)

is

a

natural

pyranocoumarin, isolated from Seseli diffusem(Roxb. ex Sm.) Sant. & Wagh.Seselin is widely important due to its biological activities, including anti-oxidant and antispasmodic properties28. The photo-responsive coumarin-based multifunctional nanoparticles were used for the controlled delivery of anticancer drug chlorambucil29. Improvement of coumarin derivatives via co-crystallization might open new avenues for next generation applications. For instance,coumarin derivatives bear luminescent properties such as coumarin-3-carboxylic acid were modified by co-crystallization with different conformers30. Theoretical insight to co-crystals by means of computational modeling enables to predict the geometry,stability, andbioavailability31. The stability of 1,3,5trinitrobenzene assembled by halogen bonding were evaluated computationally, and cocrystal forms exhibited strong stability than itsindividualcomponents32. The binding energies even associated with weak interaction were evaluated for some of coumarin derivatives33. In fact,computational predictions helped in the targeted synthesis of cocrystals for next-generation applications. By keeping above facts in mind, co-crystals of naturally occurring seselin with thiourea (Figure 1) was synthesized sucessfully. The main objectives were to assimilate the smaller molecules (thiourea in our case) in heterocyclic solid (seselin) that results in 5 ACS Paragon Plus Environment


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alteration the crystalline packing, to modify the biological properties, and to study the function of non-covalent forces that are responsible for these modifications. The 1:1 stoichiometry of co-crystal was characterized based on single-crystal X-ray diffraction analysis. The in vitro antileishmanial activity against L. major (causative agent of cutaneous leishmaniasis) promastegoates was evaluated and results showed improvement in co-crystal form as compared to seselin and thiourea. Therefore, as per approved guidelines of US-FDA the synthesized co-crystal is a potential lead for future studies against cutaneous leishmaniasis. The stable geometrical parameters were evaluated by density functional theory (DFT). The computed non-covalent interactions were in good agreement with those obtained by diffraction values. Hirshfeld surface analysisis, a powerful technique to determine intermolecular interactions qualitatively and quantitatively, was also successfully employed to quantitatively analyze the role of various interactions towards stability of arrangements in crystal lattice33,34.

Figure1. Structure of seselin-thiourea co-crystal in 1:1 stoichiometry. 3. EXPERIMENTAL SECTION 3.1.

Materials:

Commercially available solvents and chemicals were utilized without any further purification. Seselin-(8,8-dimethyl-2H,8H-benzo[1,2-b:3,4-b']dipyran-2-one)

was

isolated

from

Seseli

diffusum(Roxb. ex Sm.) Sant. & Wagh,as described by Ahmed and co-workers28.Thiourea was purchased from Merck, Germany (Index No: 612-082-0000). A small sized pestle, and mortar was used for grinding. 3.2.

Synthesis of seselin : thiourea co-crystal:


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Seselin (8,8-dimethyl-2H,8H-benzo[1,2-b:3,4-b']dipyran-2-one)was successfully co-crystallized with thiourea by using both solution reflux and grindingmethods, in the stoichiometric ratio (1:1). After dissolving the grinded mixture in methanol, left on slow evaporation at ambient temperature and pressure to obtain homogenous crystals. a. Solution Crystallization: 68.8 mg (0.3014 m. mol) seselin, and 24.5 mg (0.32 m. mol) thiourea in 1:1 molar ratio were allowed to dissolve in 5 mL methanol solution and allowed to reflux at 70°C for 3hrs. the solution kept for evaporation at RT for 2 days in order to obtain fine and shiny co-crystals. b. Grinding Method: 68.8 mg (0.3014 m. mol) seselin, and 24.5 mg (0.32 m. mol) thiourea in 1:1 molar ratio were carried out through mechanical neat grinding for 1hrin a mortar pestal, followed by methanol(2 mL) assisted grinding for 30 minutes. Resulting mixture was then dissolved in 10 mL methanol and kept on slow evaporation for 2 days to obtain suitable co-crystals for single-crystal X-ray diffraction analysis.

3.3.

Single Crystal X-ray Diffraction:

Using a compound microscope, suitable crystalof synthesized co-crystal(0.81 x 0.26 x 0.07 mm) wasselected andthen mounted on a copper pin by mean of epoxy glue for data collection. Single crystal X-ray diffraction data was collected on Bruker Smart APEX II, fitted with CCD detector diffractometer,installed with Bruker AXS kryoflex open flow cryostate(Mo Kα (0.71073 Å) radiations).Data integration, and reductionwere performed by SAINT program. The structure of compound was solved by utilizing direct method, and Fourier transformation techniques, respectively by using SHELXL97 program.Structureswere refined by using full-matrix leastsquare calculation on F2. All non-hydrogen atoms were refined anisotropic thermal parameters and were refined at geometrically idealized positions. SHELXL and PLATON were used for final refinement and various statistics. Using the ORTEP program, 3D view of molecules,and inter-molecular interaction with crystal packing were produced. 2.4. Hirshfeld surface analysis: Hirshfeld and their functions were determined by incorporating crystal explorer35, using standard settings from the calculated crystal structure parameters.Furthermore, 2D fingerprint plot was generated for visualizing percentage contribution of each contact. dnorm, di, andde surface 7 ACS Paragon Plus Environment


generated on the surface scale of -0.404__1.424 Å, 0.849__2.552 Å, and 0.848__2.597Å for dnorm, di, andde, respectively. 2.5.

Biological Screening of Co-Crystal and Seselin:

In-vitro anti-leishmanial activity against major promastigotes was evaluated by using the same procedure as used by36. 2.6.

Computational Modelling:

The geometry optimization of co-crystal was performed by density functional theory (DFT) at B3LYP/6-31(d,p) by using Gaussian 09W at super computer37. 3. RESULTS AND DISCUSIONS 3.5.

Synthesis of Co-crystal

Despite the variation of methods, our targeted co-crystal was successfully prepared by adopting two simple approaches. Neat mechanical grinding followed by methanol assisted grinding and refluxing of equiv-molar amounts of components i.e. seselin and thiourea (1:1). Both approaches were ended up to left methanolic solution of co-crystal for slow evaporation to obtain suitable crystals for X-ray diffraction analysis. The synthesis scheme for co-crystal has been illustrated in (Figure 2).

Figure2. Schematic representation of co-crystal synthesis.


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3.6.

Crystal Structure Analysis

Figure 3. ORTEP drawing of co-crystal of seselin, and thiourea [(C14H12O3) (CH4N2S)] drawn at 50% probability level. Table-1: The summary of crystal data, data collection and structure refinement parameters for synthesized co-crystal.

Crystal Parameters

Co-crystal

Empirical formula

C15H16N2O3S

Formula weight

304.36

Temperature

273(2) K

Wavelength

0.71073 Å

Crystal system

Monoclinic,

Space group

P2(1)/c

Unit cell dimensions

a = 7.1579(16) Å, b = 8.1507(19) Å, c = 24.808(6) Å, β = 96.128(5)°

Volume

1439.1(6)Å3

Z

4

Calculated density

1.405 mg/m3

Absorption coefficient

0.237 mm-1



F(000)

640

Crystal size

0.816 x 0.266 x 0.078mm

Theta range for data collection

1.651 to 25.50°

Limiting indices

h = -88, k = -99, l = -2330

Reflections Collected/ Unique

8282/2594

(Rint)

0.045

Completeness to theta = 25.49°

96.9 %

Refinement Method

Full-matrix least-squares on F2

Data / restraints / parameters

2594 / 0 / 206

Final R indices [I > 2s(I)]

R1 = 0.0388, wR2 = 0.0893

R indices (all data) Goodness of fit on F2

R1 = 0.0527, wR2 = 0.0975 1.040

Largest difference. Peak and hole.

0.297 and -0.208 e.Å-3

Structural Features: The structure of the co-crystal found to be composed of a pyranocoumarin seselin and thiourea moietyadhere in crystal lattice viaN1---H1...O3, and N2---H3...O3 noncovalent interaction(Figure. 4). The dihedral angle between coumarin ring (O1-O2/C1-C9)and six member nonaromatic pyran ring (C7/O2/C8-C11) was found to be 9.48(7)°with maximum deviation of 0.260(2)° for C-8. The bond length of 1.698(2) Å was found for S1-C14. Carbonyl group C1-O1 has bond length of 1.215(3) Å. The torsional angle of 168.31(16)° and 178.15(19)° were found for C7-O3-C12-C14 and O1-C1 -C2-C3.The summary of crystal data, data collection, and structure refinement parameters are summarized in Table-1. Crystal Packing: An overview of crystal packing of co-crystal revealed that incorporated thiourea moiety in the lattice of co crystal interacted with carbonyl functionality of seselin molecules via protons of amino group (N-H…O) without bringing any configurational changes. In the crystal lattice, the co-crystal moieties arranged in two-dimensional pattern that further stabilized by π-π interaction {(Cg1···Cg1)(O2-C1-C2-C3-C4-C9)} having minimum centroidcentroid distance of 3.691Å. Each thiourea moiety found to be connected to two neighboring thiourea molecules via N1-H1B…S1, and N2-H2B…S1 interactions to form S8 graph set repeating motif that extended to from chains running along b-axis (Figure 4). The onedimensional chains of thiourea moieties further linked with neighboring seselin molecules to form two dimensional network via N1-H1A…O1, and N2-H2B…O1 interactions, with hydrogen 10 ACS Paragon Plus Environment

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bond distances of 2.25(2) Å and 2.21(2) Å, respectively, summarized in Table2. The existence of glide

plane

symmetry

can

be

clearly

observed

in

the

Figure

4.

Figure 4. Crystal packing diagram of co-crystals [(C14H12O3) (CH4N2S)]

Table-2: Hydrogen Bond Distances in Å. D

H

A

N1

H1A H1B

N1

D-H

H...A

D...A

D-H…A

O1a

0.85(2)

2.25(2)

3.016(3)

150(2)

b

0.89(2)

3.310(2)

3.326(2)

169.7(19)

0.87(2)

2.21(2)

3.009(3)

153(2)

0.87(2)

2.55(2)

3.407(2)

168.7(19)

S1

N2

H2A

O1

N2

H2B

S1c

a

Symmetry codes #a: -1-x,-y,1-z #b: -x,-1/2+y,1/2-z #c: -x,1/2+y,1/2-z

3.7.

Antileishmanial Activity In vitro:

In vitro antileishmanial activities of the pure seselin, thiourea and its co-crystal were investigated against the L. major promastigoates. A significant enhancement in biological activity of co-crystal (IC50 = 13.2 + 1.2 µg/mL) in comparison to that of seselin (IC50 = 29.4



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+ 1.0 µg/mL) and thiourea (IC50 = 86.06+0.6µg/mL) against the tested standard pentamidine (IC50 = 5.09+0.09µg/mL) and amphotericin B (IC50 = 0.12 +0.15 µg/mL) was observed. Significant increase in anti-leishmanial activity clearly demonstrate the synergic effect of both seselin and thiourea moieties. However, detailed in vivo and mechanistic studies are required to study the mode of action. The results of the biological assays are summarized in the Table-3. .

Table-3: Biological activities of co-crystals. Sample

Leishmanicidal activity (IC50(µ µg/ml))

Seselin

29.4+1.0

Thiourea

86.06 + 0.6

Co-crystal (1)

13.2+1.2

Standard drugs

3.8.

Amphotericin B

0.29+0.05

Pentamidine

5.09+0.09

Computational Insights:

Molecular structure of co-crystal was evaluated by using density functional theory (DFT) at B3LYP/6-31 G(d,p) level. The stable molecular geometry of co crystal obtained by computational modeling is illustrated in Figure 5. The hydrogen bonding data for the components of co-crystal was evaluated theoretically. The theoretical studies supported two hydrogen bonding (N1—H1A…O1, and N2—H2A…O2) responsible for the stabilization of the co-crystal geometry with bond distance of 2.28 Å and 2.29(2) Å, respectively. Theoretical


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hydrogen bond values were found consistent with experimental values of XRD analysis (Table 4).

Figure 5. Molecular geometry of co-crystal obtained by computational modeling. Table 5: Hydrogen bonding data obtained by computational simulation D

H

A

H...A (Theoretical)

H...A (Exp)

D-H…A Theoretical

D-H…A (Exp)

N1

H1A

O1

2.28

2.25(2)

150

151

N2

H2A

O1

2.29

2.21(2)

154.24

154

The HOMO and LUMO molecular orbitals were depicted by density functional theory (DFT) at B3LYP/6-31(d,p) are presented in Figure 6. Highest occupied molecular orbitals (HOMOs) were localized on thiourea moiety that act as hydrogen bond donor (N1-H1A, N2-H2B). While LUMOs extended along the seselin skeleton acts as hydrogen bond acceptor i.e. O1as illustrated in Figure 6.



Figure 6.HOMO (left) and LUMO (right) of co-crystal depicted by DFT. Hirshfeld Surface Analysis:

Figure7. Hirshfeld surface generated on different parameters de, and di for co-crystal


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Figure8. Hirshfeld surface generated on dnorm parameters for co-crystal.

Figure9. Interaction of co crystal with the generated Hirshfeld surface in co-crystal.



Figure10. (a) Packing diagram of Hirshfeld surface with neighboring molecules (b) close packing diagram of Hirshfeld surface for co-crystal. The comparison of surface mapped on the values of dnorm with the di and de reveals the changing of contacts formed with the Hirshfeld surface (Figure 7). Highlighted area over di and de surfaces clearly shows the contacts; bright red spots vary due to the interacting atoms from the outside and inside of the surfaces. Hirshfeld surface mapped on dnorm value of compound, shows the area highlighted with bright red spots, where close contacts were formed34. Figure9 shows the red spots indicating the close contacts with Hirshfeld surface due to two hydrogen bonds O---H, and S---H, in which N2---H2B…O1 interaction is the strongest.

Figure11. (a) Shape index (b) Curvedness mapped over Hirshfeld surface for co-crystal. 16 ACS Paragon Plus Environment

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Two additional properties mapped over Hirshfeld surface reveals the probability of interaction with the neighboring molecules and planar stacking. Blue and red adjacent triangles indicate the π--π interactions, However, in our case highlighted area shows that these triangles are not clear due to the weak π--π interactions.Encircled area at one side indicates the π-hole. Curvedness surface indicates the location of surface depending upon the probability of interaction with neighboring molecules34. Packing diagram of Hirshfeld surface reveals about the packing pattern, Figure 10(a) with the neighboring molecules while Figure 10(b) shows the closed packing, depending upon the clearance of the surface packing only one-sided interactions have been generated. Figure12.1,and12.2 show the spikes are of close contacts over the Hirshfeld surface, and the highlighted blue color area, and length of spikes are due to the strength of contacts present in crystal packing. FPs indicates that most of the contributions over the Hirshfeld surface are due to H---H contact (45.2%)as the molecular surface is comprised of a sea of H atoms. Large number of H-atoms over surface supported the C-H contact to be the second one having 14.8%. Beside these interactions hydrogen bond contacts, on which the interactions are totally dependent are SH and O-H having percentages of 14.3%, and 12%, respectively38. O-H is the main contact on which crystal packing is extended further but it is contributing less than S-H. Possible reason is that S atom is contributing with Hirshfeld surface from two different sides, while O atom has only one site. Among all contacts that were contributing in crystal packing, other interaction are O-C, N-H, C-C, O-O, and O-S having 4.7%, 3.8%, 3.4%, 1.2%, and 0.6%, respectively.



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__

Figure12.1 . 2D fingerprint plots according to dnorm value (-0.404 1.424 Å) and Hirshfeld surface view about these interactions, having (a), (b), (b), (d) and (e) for total, H-H, C-H, S-H and O-H interactions in co-crystal.

__

Figure12.2 . 2D fingerprint plots according to dnorm value (-0.404 1.424 Å) and Hirshfeld surface view about these interactions, having (f), (g), (h), (i) and (j) for total, O-C, N-H, C-C, OO, and O-S interactions in co-crystal.


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Electrostatic potential:

Figure13.Electrostatic potential mapped over hirshfeld surface for co-crystal.

Electrostatic property (Figure13), mapped over Hirshfeld surface39, reveals the positive and negative end of the molecules, involved in interaction with neighboring molecules. Diagram has been extended to the neighboring molecules to elaborate the electrostatic potential. Red color represents negative potential while the blue represents the positive potential. The highlighted areas in circles represent the negative potential, which are because of sulfur atom, making S---H contact with the positive part. The rectangular highlighted area is due to oxygen of carbonyl moiety bonded viaN---H…O contact, here H atom in blue color showing positive potential.

4. CONCLUSION In conclusion co-crystal of naturally occurring seselin with thiourea has synthesized successfully. The antileishmanial activity of synsthesized co-crystal was found to be several folds more than the seselin and thiourea individually. The obtained promising results have clearly demonstrated the synergic effects of the carbonyl and amine functionalities of two molecules and promoted the ability of synthesized co-crystal as a new lead for further studies against cutaneous leishmaniasis. Furthermore, via crystallographic studies we were able to study the crystal parameters, configurations and packing of molecules in crystal lattice. The non-covalent forces involved in molecular geometry were also evaluated. The computational studies indicated the stable geometries as well as HOMO and LUMO of co-crystal. Hirshfeld surface analysis further 19 ACS Paragon Plus Environment


elaborate the qualitative and quantitative contributions of inter-molecular interactions towards crystal packing, and in addition to this electrostatic potential study showed the potential sites of the molecule for further structural modifications. The presented study further emphasizes the need of co-crystallization of the natural compounds with suitable conformers to enhance their medicinal properties.

5. CONFLICT OF INTEREST The authors has declared no competing conflict of financial interest.

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For Table of Content Use Only

Crystal Engineering of Naturally Occurring Seselin to Obtain Co-crystal with Enhanced Antileishmanial Activity, Hirshfeld Surface Analysis and Computational Insight Ejaz Hussain †, Rajesh Kumar †, M. Iqbal Choudhary †‡, SammerYousuf †*. †

H.E.J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi-75270, Pakistan. ‡

Department of Biochemistry, Faculty of Science, King Abdulaziz University, Jeddah-21412, Saudi Arabia.

*Correspondence author: H. E. J. Research Institute of Chemistry, International Center for Chemical and Biological Sciences, University of Karachi, Karachi-75270, Pakistan. Tel: +92-21-34824924-5 Fax: +92-21-4819018-9 E-mail address: [email protected]

Current study demonstrated the synthesis, structural studies and anti-leishmanial activity evaluation of the co-crystal of naturally occurring seslin with thiourea. Synthesized co-crystal showed improved anti-leishmanial activity against promastegoates of L. major responsible for cutaneous leishmaniasis. DFT was employed to obtain HOMOs and LUMOs of co-crystal followed by Hirshfeld surface analysis to quantitively analyze various intermolecular interactions involved in crystal packing.




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Crystal Engineering of Naturally Occurring Seselin to Obtain a Co

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