and Synthesis and Anticancer Activity ... Synthesis and Anticancer Activity of Triazole Linked Macrocycles and Heterocycles

Synthesis of macrocylic enones starting from alkyl ether and triazole as a linker was achieved using click reaction and intramolecular aldol condensation. The newly synthesized macrocyclic enone was successfully utilized as a dipolarophile in 1,3-dipolar cycloaddition. The dipoles generated from hydrazine hydrochloride, hydroxylamine and guanidine hydrochloride were reacted with macrocyclic enone to give a new class of spiro aminopyrimidines, phenyl pyrazoles and isoxazoles grafted macrocycles in good yield. The structures of newly synthesized compounds were confirmed with IR, NMR and mass spectroscopy and evaluated for their anti cancer activity. 64.2, 63.2, 50.8, 35.9, Anal. for C H N : C, 63.62; N, 14.13; Found: C,


Introduction
Carbohydrates are most important class of bio-molecules, their structural components have an important role in biological processes and organic synthesis. 1 In the chemical, pharmaceutical, food, cosmetic and detergent industries they act as readily available intermediates stocks for large scale applications 2 and also they have an important role in cell physiology in the form of glycoconjugates (glycolipids, glycoproteins and polysaccharides) and in many biological processes such as intercellular recognisation, bacterial and viral infection, cancer metastasis, apoptosis and neuronal proliferation, etc. 3 The introduction of a carbohydrate moiety into a system often imparts interesting properties such as hydrophilicity, lowered noxious and escalated bioactivities; 4 organic chemists have linked carbohydrates to various biologically potent compounds to escalate their biological applications, such as steroids, amino acids and other therapeutic agents. 5 One of the methods used to link a carbohydrate moiety with a potential compound is via a triazole ring using the well known click-chemistry reaction. 6 The strategy of linking a carbohydrate moiety with another species via a triazole ring is gaining importance in organic synthesis, natural products chemistry and bio chemistry. 7 The stability, polar nature and possible hydrogen bonding ability of a triazole ring combined with the biocompatibility and presence of stereogenic centers, the stereogenic centers of a carbohydrate moiety make glucal-based triazoles very interesting for organic synthetic chemists.
Macrocyclic compounds with large cavities are found to have potential application in chemistry, biology and nanotechnology, 8,9 With potent biological activities, heteroatoms-containing macro cyclic compounds are present in natural products. 10 Heterocyclic compounds are known to interact with various proteins and heterocyclic units are constituent parts of magnificent molecular ligands; 12 such compounds can also act as magic eye for chiral molecules and can be used for selective metal ion and anion remembrance. 13,14 The Cu(I)-catalyzed alkynes -azide cycloaddition is the most useful modality for the fashioning of diversification of 1,2,3-triazole grafted macrocycles. 15 In recent years 1,2,3-triazoles have large attraction in supramolecular chemistry because of their dual nature to act as both hydrogen bond donors and acceptors 16,17 due to their firmness and lyomerous properties, these triazoles can be of more conspicuous use as a non-peptide inhibitors. 18 Furthermore, they exhibit large variety of medical activities. 19 Triazole glycosides are also present in the structures of various antiviral drugs such as Ribavirin and β-D-ribofuranosyl-1,2,4-triazole-3-carboxamide. 20 Isoxazole derivatives are pertinent class of bioactive molecules, which express glaring activities such as protein tyrosinephosphatase 1 inhibitors, 21 antiviral, 22 antihelmintic, 23 antiinflammatory, 24 anticonvulsant, 25 insecticidal, 26 antitubercular, 27 immunomodulatory, 28 and hypolipermic. 29 Moreover pyrazoles and their derivatives could be considered as possible antimicrobial agents, 30 activities of the other derivatives include antidepressant, 31 antiarthritic 32 and cerebroprotectors. 33 Some aryl pyrazoles were reported to act as non nucleoside human immunodeficiency virus (HIV-1) reverse transcriptase inhibitors, 34 COX-2 inhibitors, [35][36][37] activators of the nitric oxide receptors and soluble guanylate cyclase activity. 38 On the other hand, the pyrimidines have special place and have contributed exceptionally to biological and medicinal fields, 39 with activities such as antitubercular, 40 and calcium channel blockers, 41 and also many pyrimidines 42 have displayed diverse pharmaceutical activities depending upon the geometry and type of substituents attached to the ring. 43 3-Azido-3-deoxythymidine (AZT), 44 a pyrimidine derivative, has been found to be an eloquent antiviral agent against HIV type 1 in vitro, and has been found to decrease mortality and opportunistic infections in patients with AIDS.

Results and Discussion
The key intermediate 8 required for the synthesis of compounds 9, 10 and 11 was prepared according to the procedure outlined in the Scheme 1. 1-(2-(4-Bromobutoxy)phenyl)ethanone (2), prepared from 2-hydroxyacetophenone by treating with 1,4-dibromopropane in DMF in the presence of K 2 CO 3 , followed by sodium azide, gave its corresponding azide, is converted into triazole 7 (82%) by using 1,3-dipolar cycloaddition with propargyl ether 4 carried out at ambient temperature in the presence of CuSO 4 and sodium ascorbate in a mixture of 1:1 CH 2 Cl 2 -H 2 O. Acid hydrolysis of 5 in 60% AcOH furnished the diol 6, which on oxidative cleavage with NaIO 4 gave the aldehyde 7, which is subjected to internal aldol condensation to give macrocycle 53 8 (Scheme 1). Compound 8 was then reacted with hydroxylamine, hydrazine hydrochloride and guanidine hydrochloride at reflux temperature to gave macrocyclic derivatives 9, 10 and 11.
The key intermediate 20 required for the synthesis of compounds 21, 22 and 23 was prepared according to the procedure outlined in the scheme 2. 1-(2-(4-Bromobutoxy)phenyl)ethanone (2), prepared from 2-hydroxyacetophenone by treating with 1,4-dibromopropane in DMF in the presence of K 2 CO 3 , followed by sodium azide to give its corresponding azide, is converted into triazole 7 (82%) by using 1,3-dipolar cycloaddition with propargyl ether 16, carried out at ambient temperature in the presence of CuSO 4 and sodium ascorbate in a mixture of 1:1 CH 2 Cl 2 -H 2 O, oxidation of compound 18 with IBX gave aldehyde, which is subjected to internal aldol condensation to give macrocycle 53 20 (Scheme 2). Compound 20 was then reacted with hydroxylamine, hydrazine hydrochloride and guanidine hydrochloride at reflux temperature to gave macrocyclic derivatives 21, 22 and 23. The structures of synthesized compounds were determined by IR, NMR, MS spectra and evaluated for their anticancer activity.  from the plotted absorbance data for the dose-response curves. IC 50 values (in μΜ) are indicated as mean ±SD of three independent experiments. From the data reported in Table 1, most of the prepared compounds possessed significant cytotoxicity effect on all the tested cell lines and potencies of some of the compounds were comparable to the standard doxorubicin, the most widely used drug for the treatment of tumors. Among the tested compounds 9 and 23 showed the most potent activity against MCF-7 cell line with IC 50 value of 1.82 and 1.90 μΜ, whereas 10, 11, 21 and 22 showed promising activity against MDA-MB-231 and HeLa cell lines.

Experimental
Commercial grade reagents were used as supplied, solvents (except those of analytical reagent grade) were dried and purified according to the literature when necessary. Reaction progress and purity of the compounds were checked by thin-layer chromatography (TLC) on pre-coated silica gel F254 plates from Merck and compounds were visualized either by exposure to UV light or by dipping in 1% aqueous potassium permanganate solution. Silica gel chromatographic columns (60-120 mesh) were used for the separations. By using Perkin-Elmer 141 polarimeter optical rotations were measured on a 2 mL cell with a path length of 1 dm with CHCl 3 or CDCl 3 as the solvent. By using Fisher-Johns apparatus all melting points were measured and are uncorrected. IR spectra were recorded as KBr disks on a Perkin-Elmer FT IR spectrometer. The 1 H NMR and 13 C NMR spectra were recorded on a Varian Gemini spectrometer (300 MHz for 1 H and 75 MHz for 13 C). Chemical shifts are reported as δ ppm against TMS as the internal reference and coupling constants (J) are reported in Hz units. Mass spectra were recorded on a VG micro mass 7070H spectrometer. Elemental analysis (C, H, N) were determined by a Perkin-Elmer 240 CHN elemental analyzer and were within ±0.4% of theoretical values.
To the solution containing alkyne 4 (1.45 g, 4.8 mmol), azide 3 (1.50 g, 6.4 mmol) in dichloromethane (10 mL) and water (10 mL) were added CuSO 4 •5H 2 O (0.110 g) and sodium ascorbate (0.114 g); the resulting suspension was stirred at room temperature for about 6 h, the mixture was diluted with 5 mL dichloromethane and 5 mL water. The organic phase was separated, washed with brine, dried over sodium sulphate and concentrated under reduced pressure; the crude product thus obtained was purified by column chromatography on silica gel (60-120 mesh, hexane/EtOAc 65:35) to afford 5 (3.290 g, 6

]dioxaazacyclohexadecin-12(5aH)-one (8)
To the solution of diol 6 (2.4 g, 4.88 mmol) in CH 2 Cl 2 (5 mL), NaIO 4 (0.530 g, 2.48 mmol) was added at 0 °C and stirred at room temperature for about 6 h. The reaction mixture was filtered and washed with CH 2 Cl 2 (2×10 mL), dried over Na 2 SO 4 and evaporated to give keto aldehyde 7 (2 g) in quantitative yield as a yellow liquid, which was used for the next reaction.
Boron trifluoride diethyl etherate (690 μL of a 40 w% solution in diethyl ether, 11.02 mmol) was added drop wise and the reaction mixture was stirred for 90 min. The mixture was poured into a saturated solution of NaHCO 3 . The organic layer was washed with water, dried over Na- 2

Conclusions
A series of novel furanose and pyranose macrocyclic enone heterocycles was prepared and evaluated for their anticancer activity. Among the tested compounds 9 and 23 showed the most potent activity against MCF-7 cell line with IC 50 value of 1.82 and 1.90 μΜ, whereas 10, 11, 21 and 22 showed promising activity against MDA-MB-231 and HeLa cell lines.