Serendipitous N,S-difunctionalization of triazoles with trifluoromethyl-β-diketones: access to regioisomeric 1-trifluoroacetyl-3-aryl-5-(2-oxo-2-arylethylthio)-1,2,4-triazoles as DNA-groove binders

In the present research work, a serendipitous regioselective synthesis of DNA targeting agents, 1-trifluoroacetyl-3-aryl-5-(2-oxo-2-arylethylthio)-1,2,4-triazoles, has been achieved through the one-pot cascade reaction of 3-mercapto[1,2,4]triazoles with trifluoromethyl-β-diktetones in presence of NBS instead of the cyclized thiazolo[3,2-b][1,2,4]triazole. The present protocol offered a unique approach for functionalizing both N-acylation and S-alkylation in a concerted fashion. The structures of the regioisomeric products were thoroughly characterized by heteronuclear 2D NMR experiments. Facile scalability and excellent atom economy through easily available starting reactants are the notable features of the present sustainable protocol. Targeting tumor cell DNA with minor groove-binding small molecules has proven highly effective in the recent past, drawing significant attention for combating tumor-related afflictions. In this context, the synthesized analogs were primarily screened for their ability to bind with the DNA duplex d(CGCGAATTCGCG)2 using molecular modeling tools. Additionally, the most promising compound 14m was deployed as a probe for DNA sensing and interaction mechanisms with calf thymus (ct)DNA through various spectral techniques at a physiologic temperature of 37 °C. It has been found that the compound demonstrated a strong binding affinity (Kb = 1 × 105 M−1) with double-helical DNA, particularly within the minor groove, resulting in the formation of a stable complex through static quenching (Kq = 5.86 ± 0.11 × 1012 M−1 s−1). The fluorescent displacement assay confirmed that the quencher binds to the minor groove of ctDNA, further supported by circular dichroism and viscosity studies.


Introduction
Organouorine chemistry irrefutably holds immense importance in the realm of scientic exploration, particularly in the pharmaceutical and agrochemical industries, and makes up more than 50% of the best-selling drug molecules approved by the US Food and Drug Administration (FDA). 1 Within the category of organouorine compounds, those containing the tri-uoromethyl (CF 3 ) group are particularly noteworthy due to their potent electron-withdrawing properties and considerable hydrophobic surface area.The inclusion of the CF 3 group in an organic compound can signicantly alter a plethora of physiochemical characteristics, leading to improved effectiveness, specicity, ability to dissolve in fats, ability to be absorbed by the body, resistance to metabolism, electrical charge, ability to pass through membranes, polarity, and durability of C-F bond compared to C-H bond. 2,35][6] Indeed, numerous successful drugs have capitalized on the benets of incorporating the triuoromethyl group into their chemical makeup.][9] 1,2,4-Triazoles belong to an important class of heterocyclic compounds containing three nitrogen atoms in a vemembered aromatic ring.Triazoles are stable for metabolic degradation and show target specicity, as the three nitrogen atoms can act as hydrogen bond acceptors or donors at the active site of the biological receptors and can modulate their RSC Advances PAPER activity accordingly. 102][13][14] It is well documented that the integration of CF 3 with 1,2,4-triazoles plays a substantial role in the drug development program and agrochemical industry. 15Some biologically representative examples of triuoromethyl-linked mercapto [1,2,4]triazole-based analogs (1-7) are shown in Fig. 1.
7][18] The research indicated that small organic molecules interact with DNA in two distinct ways; either by intercalating between base pairs or by recognizing the grooves.The major groove offers more opportunities for hydrogen bonding, but its pocket for small molecules is broader and less deep than that of the minor groove.Hence, the minor groove is the preferred site for small ligands, which creates a more hydrophobic environment between the base pairs.In contrast, proteins and peptides tend to favour the major groove for binding. 19,20The minor groove of DNA plays a pivotal role in a variety of molecular interactions and target modications, rendering it a signicant point of interest.Drugs that bind to the minor groove of DNA have garnered considerable attention for their ability to combat tumor-related afflictions. 18,21In recent years, researchers have discovered compounds that bind to DNA and can alter its functions, offering the potential for new forms of chemotherapy.Through extensive biochemical studies, these compounds have been considered as having antibiotic, antiviral, or antitumor properties.Therefore, it is essential to investigate the dynamics of these interactions within the natural environment of living cells and the development of corresponding investigative tools.
Considering the unique properties of the CF 3 group and the signicant biological applications of 3-mercapto-1,2,4-triazole derivatives, it was deemed advantageous to incorporate the triuoromethyl group into the triazole ring.Pertinent to the present research, the development of a general and convenient approach for the assembly of triuoromethyl decorated 1,2,4triazole-based derivatives is still highly desirable.In this context, we aimed to synthesize new triuoromethylated isomers of thiazolo [3,2-b] [1,2,4]triazole by reacting 3-mercapto [1,2,4]triazoles 8 with triuoromethyl-b-diketones 9 in the presence of NBS.However, open-chain analogs were obtained which were investigated for DNA binding properties, and ex vivo studies were performed using various spectroscopic techniques.

Results and discussion
Recently, we have reported visible-light-mediated regioselective synthesis of thiazolo [3,2-b] [1,2,4]triazoles by the reaction of 2bromo-1,3-diketones, with 3-mercapto [1,2,4]triazoles under aqueous conditions in excellent yields. 22,23In the quest for the development of CF 3 -integrated novel therapeutic agents, we envisaged exploring the reaction of 3-mercapto [1,2,4] To elucidate our work hypothesis, 5-(4-methylphenyl)-3mercapto [1,2,4]triazole 8a and 4,4,4-triuoro-1-phenylbutane-1,3dione 9a in the presence of NBS were selected as the model reaction partners to screen the reaction conditions.The reaction was monitored by TLC (ethyl acetate : petroleum ether, 30 : 70, v/v as eluent) at regular intervals.The rst reaction was carried out under visible-light conditions; similar to those already successfully employed for the regioselective synthesis of non-uorinated thiazolo[3,2-b] 1,2,4 triazoles by our research group, 22,23 however, the reaction could not be initiated even aer irradiation of 5 h (run 1, Table 1).Thereaer, the reaction was explored in ethanol (EtOH) and a mixture of EtOH and H 2 O in different ratios under visible light, TLC indicated the partial consumption of reactants and resulted in low yields (runs 2-4, Table 1).Reuxing in EtOH pleasingly afforded the product in 71% yield aer 2 h (run 5, Table 1), however, the use of PTSA as an additive did not improve the reaction outcomes (run 6, Table 1).Thereaer, the condensation reaction was screened in different solvents viz.DCM, THF, and DMF under reuxing conditions (run 7-9, Table 1), however, no signicant results were observed in terms of yield or reaction time.Shiing the reaction conditions to a solvent-free environment caused a slowdown of the reaction rate and decreased the reaction yield (run 10-11, Table 1).Based on the screening results, the reuxing of substrates in EtOH was selected as the best condition for this transformation.In all the cases, we have notably observed the consistent formation of a single product with the same R f values.
It is noteworthy to highlight here that inspired by Sherif et al. 2,4]triazoles synthesis in acidied acetic acid (AcOH/H + ), 24 our study replicated the acidic conditions using 8a and 9a in presence of NBS.However, the outcomes closely mirrored our previous ndings, 23 revealing the exclusive formation of a single product identied as 6-phenyl-2-(4-methylphenyl)thiazolo[3,2-b][1,2,4]triazole, conrmed through comparison of its melting point and spectral data with literature values. 25he preliminary examination of the spectral data of the obtained product gestured towards some interesting reaction pathway of 5-(4-methylphenyl)-4H-3-mercapto [1,2,4]triazoles 8a with triuoromethyl-b-diketone 9a to afford an unexpected product, which does not correlate with the data desired for the expected uorinated thiazolotriazoles 10, 11, 12 or 13 (Scheme 2), as obtained in our earlier non-uorinated thiazolotriazole analogs. 22,23he IR spectrum of the obtained product 14a/15a displayed an additional strong C]O absorption band at 1683 cm −1 along   with the expected C]O absorption band at 1597 cm −1 indicating the presence of two carbonyl groups in the product. 13C NMR spectrum also depicted the presence of two carbonyl carbons at d 194.6 ppm and 161.9 ppm along with the desired aromatic carbons, however, an additional peak for the methylene group at d 39.2 ppm has been observed in the spectrum.Furthermore, the 1 H NMR spectrum also depicted an additional singlet integrating for two protons in the aliphatic region ( The 2D NMR correlation results obtained for compounds 14a and their 1 H, 13 C, and 19 F chemical shi values are presented in Fig. 2. Following an in-depth structural analysis of the unexpected product, we made efforts to induce cyclization of the cleaved product 14 employing Aliquat 336 as a phase transfer catalyst and exploring diverse basic conditions (KOH, K 2 CO 3 , C 2 H 5 ONa, DABCO, and trimethylamine) to obtain the desired cyclized product 10.Unfortunately, none of these reaction experiments yielded the anticipated outcome (Scheme 3).
To explore the biological potential of the newly synthesized compound, we conducted a comprehensive investigation into the substrate scope and limitations of this process.Variously substituted 3-mercapto[ 1,2,4 ]triazole and uorinated 1,3-diketone compounds were employed, and the results are depicted in Fig. 3.The outcomes indicated that, in all cases, the reaction proceeded smoothly, yielding 14a-o as the nal product.Although different substituent groups had a slight effect on the yields, the differences were minimal, and it was challenging to ascertain the specic impact of any individual substituent.

DNA binding studies
Molecular docking studies.Computational chemistry plays a crucial role in identifying the formation of complexes between organic molecules and biological receptors. 28,29Therefore, we conducted an in-depth study to investigate the interaction between acyl-functionalized triazole derivatives and a doublestrand DNA dodecamer d(CGCGAATTCGCG) 2 (PDB ID: 1BNA) by applying molecular docking screenings to all synthesized compounds, denoted as 14a-o.Table 2 contains a summary of the calculated binding energy values, for the complexes between the receptor and ligand.Ligand 14m having 4-methoxyphenyl substitution on triazole and 4-methyl substituted diketone was found to be the most effective and strongest binder with the DNA dodecamer based on the docking conformations and lower DNA binding energy of ligand 14m.The best docking pose of compound 14m had a binding affinity of −9.0 kcal mol −1 , visualized in BIOVIA Discovery Studio Visualizer.
Through analysis of docking, it has been discovered that the triazole derivatives bind in the minor groove section of base pairs particularly in the guanine-rich region through various non-covalent interactions, such as hydrophobic interactions (palkyl, p-sulfur, etc), conventional hydrogen bonding, halogen interactions, and van der Waals forces.By examining the 2D plots of the best dock complex (DNA-14m), it was determined that both the carbonyl groups of the open-chain functionalized triazole derivative played a crucial role in conventional hydrogen bonding, with additional supportive interactions provided by the sulfur atom, and triuoromethyl group (Fig. 4).
It is signicant to mention that the corresponding cyclized derivatives 10 had a low docking score (−6.0 to −7.2 kcal mol −1 ), which may be attributed to the presence of only one carbonyl group, resulting in a decreased likelihood of H-bond formation.Additionally, the cyclized structure limits the exibility of the molecule, thereby restricting its binding strength.
UV-visible studies.Electronic absorption spectroscopy is a highly effective method for analyzing how organic molecules bind with DNA. 29Typically, changes in hyperchromism and hypochromism are the key spectral features of DNA's doublehelix structure.Hyperchromism refers to the disruption of the secondary structure of DNA, while hypochromism suggests that the complex's binding mode with DNA is either an electrostatic effect or intercalation, which can stabilize the DNA duplex.The presence of a red shi indicates that the DNA duplex is being stabilized. 30To demonstrate the possibility of acylfunctionalized 1,2,4-triazoles binding with calf thymus (ct) DNA, spectroscopic titration of 14m with DNA has been performed for different ratios of [14m]/[DNA] while maintaining a constant DNA concentration (72 mM) in Tris-HCl buffer.Fig. 5 shows the UV spectra of DNA when exposed to different concentrations of 14m at 37 °C.The absorption spectra of ctDNA showed changes when titrated with triazole molecules, with an increase in intensity at the wavelength of 260 nm up to 35.8% with a 6 nm red shi (bathochromic shi) in the wavelength.This indicates that the interaction between the complexes and DNA occurs through the direct formation of a new complex with the double-helical ctDNA in the groove region.The increase in absorption intensity at 260 nm is due to the exposure of purine and pyrimidine bases in DNA caused by the binding of the complex to the DNA.This type of binding may have caused a slight change in the DNA's conformation.
Aer taking into consideration the aforementioned ndings, we proceeded to delve deeper into how the DNA-triazole (14m) complex interacts.We aimed to gain a better understanding of the mode of interactions and binding strength.To this end, we utilized various methods such as uorescence quenching, CD spectral, and viscosity analysis.
Fluorescence quenching studies.Fluorescence techniques have been highly effective in facilitating quantitative investigations of the equilibria and kinetics of drug-DNA interactions. 31,32he binding of organic species with biomolecules results in changes in uorescence properties such as intensity or anisotropy.By utilizing equilibrium titration methods, these changes can be measured to accurately determine the stoichiometry, affinity, and thermodynamics of the binding interaction.Fig. 6 presents the emission spectra of ctDNA (72 mM) and its uorescence titration with compound 14m (0-26 mM).The uorescence spectra were recorded within the range of 300-500 nm at 37 °C, the peak excitation wavelength is at 290 nm, while the highest emission wavelength is at 330 nm.As the concentration of 14m increases, the uorescence intensity of ctDNA rapidly decreases.The uorescence is reduced by 58.87% when the DNA concentration rises to 26 mM.
The reduction in uorescence intensity in the DNA spectrum is usually caused by quenching mechanisms such as static quenching, dynamic quenching, and mixed quenching.Static quenching occurs due to complex forms between biomolecule and quencher in the ground state, while dynamic quenching Paper RSC Advances occurs due to collisions in the excited state.Through the utilization of Stern-Volmer constants (K sv ) and quenching constants (K q ), the efficacy of quenching in the spectrum can be comprehended.To this end, graphs were generated by plotting the ratio of uorescence blank DNA and DNA+14m (F 0 /F) against increments of 14m, thus revealing the mechanism  (Fig. 7A).The quenching constant was determined by assuming the average lifetime to be 10 −8 seconds.The quenching constant (K q = 5.86 ± 0.11 × 10 12 M −1 s −1 ) was found to be higher than the scattering constant (10 10 L mol −1 s −1 ), indicating that the quencher 14m forms a complex with DNA through static quenching. 33he value of the slope of the graphs determines the Stern-Volmer constant (K sv ) (eqn (1)).
F 0 represents the uorescence intensity of pure DNA, however, F refers to the uorescence intensity of DNA-14m complex (0-26 mM).[Q] signies the molar concentration of 14m, s o denotes the average lifetime.
Furthermore, to understand how strongly DNA and 14m are bound together, we have calculated the intrinsic binding constant (K b ) by creating Scatchard graphs (Fig. 7B).The binding constant K b and number of binding sites n were calculated employing the Scatchard equation (eqn ( 2)) (Table 3).
However, a change in Gibbs free energy (DG°) helps in the determination of the spontaneity of the binding procedures.
DG°, K b , and R refer to the Gibbs free energy, binding constant at temperature T and gas constant (8.314J mol −1 K −1 ) respectively.
The intrinsic binding constant value has been determined to be within the range of 10 5 , signifying the robust and enduring binding between the triazole molecule and DNA through 1 : 1 binding stoichiometry.The results reveal the remarkable and effective bonding properties of the triazole compound with DNA, underscoring its potential as a valuable asset in diverse biological contexts.Additionally, the negative value for Gibbs free energy change DG°elegantly supports the feasibility and favorability for the formation of the DNA-14m complex.Table 3 Stern-Volmer constant (K sv ), quenching constant (K q ), binding constant (K b ), the number of binding sites (n), and Gibbs free energy (DG°)

Paper RSC Advances
The displacement assay is an important tool for identifying how DNA and a ligand molecule interact.Two well-known dyes, Ethidium bromide (intercalator) and Hoechst 33 258 (groove binder), are commonly used to determine whether a ligand molecule intercalates or binds to the grooves of DNA.The study tested the interaction of a triazole derivative (14m) with DNA using two different dyes (EtBr and Hoechst).The results showed that compound 14m did not displace the intercalating dye from the DNA-EtBr complex, indicating it does not interact with DNA through intercalation.there was a signicant reduction in uorescence intensity of the DNA-Hoechst complex with increasing concentration of compound 14m at 37 °C, suggesting it interacts with DNA through groove-binding modes (Fig. 8).
Circular dichroism (CD) spectroscopy.CD spectroscopy proves to be valuable in identifying alterations in the structure of DNA as a result of drug-DNA interactions. 34,35The 275 nm positive band and 245 nm negative band, which correspond to base stacking and right-handed helicity respectively, are highly responsive to how small molecules interact with DNA.The modications in the CD signals of DNA when exposed to drugs can usually be attributed to alterations in the DNA structure.Smaller molecules that bind to the grooves and have electrostatic interactions with DNA have little to no impact on the basestacking and helicity bands.However, intercalation results in heightened intensities of both bands and stabilizes the DNA's right-handed B conformation, as demonstrated by methylene blue.The CD spectra of 14m and double-stranded DNA can offer valuable insights into their interactions.The CD spectrum of free DNA solution has a positive band at 275 nm and a negative band at 245 nm due to base stacking and helicity in the righthanded B form.Compound 14m has no CD spectrum alone, but has a titrated CD spectrum when interacting with DNA.The CD spectra of DNA did not display any signicant change when titrated with 14m, indicating the groove-binding nature of the triazole derivative (Fig. 9).This data was consistent with results from UV-visible and uorescence studies.
Viscosity measurements.The measurement of viscosity in drug-DNA complexes is a reliable way to investigate their interaction. 36Intercalative binding, which occurs when a drug inserts itself between the base pairs of DNA, causes the DNA helix to lengthen and the viscosity to increase.However, if the drug interacts with DNA through electrostatic or groove binding, there is no signicant change in viscosity.To examine the effect of 14m on CT-DNA, a graph of (h/h o ) 1/3 vs. [14m]/ [DNA] was plotted.The results showed that as 14m was added to the CT-DNA solution, the viscosity remained constant (Fig. 10).This indicated that 14m binds to DNA externally and did not intercalate into the DNA helix.The relative viscosity of the solution was determined using the relation below (eqn (4)): 19,37   where h 0 & h are the viscosities of DNA in the absence and presence of 14m respectively.t DNA , t complex , t o is the average ow time of pure DNA, DNA-14m complex, and Tris-HCl buffer respectively.

Conclusion
On the whole, a strategically novel one-step protocol for regioselective 1,3 N,S-difunctionalization of triazoles, which allows an expedient construction of CF 3 -containing architectures through an unprecedented reaction between 3-mercapto [1,2,4]  triazoles and triuoromethyl-b-diketones was disclosed.This methodology for the synthesis of various uorinated triazoles has great potential for applications in related chemistry.In silico molecular docking analysis evidenced that triuoromethylated triazole derivatives exhibited superior binding efficacy within the minor groove of the DNA double helix when compared to their cyclic counterparts.Spectroscopic results represented that binding of triazole derivatives to DNA resulted in signicant changes in the structure and conformation of DNA in a concentration-dependent manner and acted as groove binder (K b = 1 × 10 5 M −1 ) via a static mode of quenching (K q = 5.86 ± 0.11 × 10 12 M −1 s −1 ).Moreover, circular dichroism and viscosity measurements supported the DNA groove binding nature of the triazole derivatives.

Materials and methods
An electrical digital Melting Point Apparatus (MEPA) was used to examine melting points in open capillaries and were not corrected.Analytical TLC was performed using Merck Kieselgel 60 F254 silica gel plates and visualized under UV light (254 nm).IR spectra were recorded on Buck Scientic IR M-500 spectrophotometer in KBr pellets (y max in cm −1 ), 1 H (400 Hz), and 13 C NMR (100 Hz) spectra for the analytical purposes were recorded on a Bruker instrument, using CDCl 3 and DMSO as a solvent and the chemical shis are expressed in parts per million (ppm) and coupling constant J in Hz with TMS as internal standard.High-resolution mass spectra (HRMS) were measured in ESI + mode at MRC, MNIT, Jaipur.3-Mercapto-1,2,4 triazoles and 1,3diketones were prepared as per the literature procedure, 23,[38][39][40][41] however, commercially available NBS (Avra Chemicals, India) were used without any purication.
General procedure for the synthesis of 1-triuoroacetyl-3-aryl-5-(2-oxo-2-arylethylthio)-1,2,4-triazoles 14a-o Triuoromethyl-b-diketones 9 (1.0 mmol) and NBS (0.178 g, 1.0 mmol) were homogenized thoroughly in a dry pestle mortar until a thick paste was formed and were subsequently added with an ethanolic solution of 5-aryl-3-mercapto[1,2,4]triazole 8 (1.0 mmol) in the round bottom ask.The reaction mixture was reuxed for 2-2.5 hours.The reaction progress was monitored with TLC using ethyl acetate-petroleum ether (30 : 70, v/v).On completion of the reaction, the solvent was evaporated at reduced pressure on the rotatory evaporator and the residue thus obtained was neutralized with a saturated solution of sodium bicarbonate and extracted with ethyl acetate.The obtained solid was recrystallized with ethanol and dried to afford pure 14 with 65-75% yields.The products were characterized by IR, 1 H, 13 C NMR, and HRMS spectrometry.spectroscopy with an attenuance ratio A 260 /A 280 between 1.8 and 1.9.Therefore, it was used without further purication.The DNA concentration was measured using spectrophotometry at a physiological pH of 7.4 and an extinction coefficient value of 6600 L mol −1 cm −1 at 260 nm wavelength.
Absorbance values were recorded on a double beam Thermo Scientic's Evolution 300 spectrophotometer and uorescence measurements were performed on a Hitachi F-4700 quantum north-west 5J20700 fortied with a xenon lamp, using a quartz cuvette of path length 1 cm.The CD measurements of the DNA-14m complex (Far-UV, 200-250 nm) were recorded on a J-815 spectrophotometer (JASCO, Japan) at room temperature using a quartz cuvette with a path length of 10 mm.
Preparation of stock solution.A solution containing 14m at a concentration of 1 mM was made in DMSO.A uniform mixture of ctDNA was created by stirring it in Tris-HCl buffer using a vortex.The DNA concentration was measured at 72 mM using Beer-Lambert Law with a molar extinction coefficient of 6600 L mol −1 cm −1 for a single DNA strand.

aScheme 2
Scheme 2 Unexpected product formation from the reaction of 8a and 9a.
d 4.77 ppm) indicating the formation of an unexpected open chain product from the unusual reaction of 8a and 9a.Additionally, the DEPT spectrum depicted the presence of ve methines (CH), one methylene (CH 2 ), and one methane (CH 3 ) carbon.To be further certain about the structure; we have recorded the mass spectrum of the obtained product.The mass spectrum depicted an intense peak, m/z value of 406.0754 for [M+1] peak, which is notably higher than the expected value for the uorinated thiazolotriazoles 10, 11, 12 or 13 value (388.0653).Thus, the preliminary examination of spectra indicated the formation of an open chain analog instead of cyclized thiazolotriazoles, which was identied as 1-triuoroacetyl-3-(4-tolyl)-5-(2-oxo-2phenylethylthio)-1,2,4-triazole 14a or 1-benzoyl-3-(4-tolyl)-5-(2oxo-2-triuoromethylethylthio)-1,2,4-triazole 15a by the combined analysis of spectral data including IR, 1D NMR and HRMS spectrum.Conclusive evidence for the formation of 1-triuoroacetyl-3-aryl-5-(2-oxo-2-arylethylthio)-1,2,4-triazole regioisomer 14 was obtained by collective results from the rigorous study of heteronuclear 2D NMR experiments of the compound 14a.The chemical shi values of protons and their corresponding carbons were assigned using ( 1 H-13 C) HSQC spectrum.Further, the ( 1 H-13 C) HMBC results showed cross-peaks of carbonyl carbon (d 194.6 ppm) with 2 0 /6 0 -H proton (d 8.02 ppm) of the phenyl ring indicating the presence of carbonyl carbon with aryl ring and the cross peak of carbonyl carbon (d 194.6 ppm) with CH 2 (d 4.77 ppm) conrmed the presence of CH 2 -CO-Ar fragment, ruled out the possibility for the formation of regioisomer 15a.Similarly, the cross peak of C-5 (d 159.4 ppm) of the triazole nucleus with CH 2 (d 4.77 ppm) indicated the presence of 2-oxo-2-arylethylthio group at position 5 of the triazole ring.Other correlations are seen from protons of CH 3 (d 2.29 ppm) with C-4 00 (d 138.9 ppm), C-3 00 /C-5 00 (d 130.0 ppm).The ( 19 F-13 C) HMBC results displayed the correlation of uorine (d −73.4 ppm) with carbonyl carbon (d 161.9 ppm).All expected correlations were validated in the COSY and NOESY spectrum, sufficient to support the substituents pattern around the triazole nucleus and all our data are consistent with structure 14a as the reaction product.

Table 1
Screening of the reaction conditions a