Tricyclic spiro[chromane-2,4'-piperidin]-4(3/7)-one with 1 ,3,4-oxadiazole linkers compositions and process for preparation thereof.

Field of invention:

The present invention relates to Tricyclic spiro[chromane-2,4'-piperidin]- 4(3H)-one with 1 ,3,4-oxadiazole linkers and compositions thereof. More particularly it relates to the said compounds with 1 ,3,4-oxadiazole linkers as potent precursors of anti-tubercular agents. The invention provides for 35 compounds and formulations thereof having marked activity as antituberculosis. The invention also provides a process for preparation of those compounds.

Background of invention:

The present invention relates to the tricyclic spiro [chromane-2,4- piperidin]-4(3/-/)-one with 1 ,3,4-oxadiazolederivatives useful as potent anti-tubercular agents. The invention also provides pharmaceutically acceptable compositions comprising the compounds of the invention and methods of using the compositions in the treatment of various disorders. Tuberculosis (TB) is one of the ancient chronic infectious diseasesto avow the lives of around 1.7 million people per year.lt is mainly caused by the bacillus Mycobacterium tuberculosis(Mtb) and claimed to be world’s second most common cause of death from infectious diseases, after AIDS. Traditional therapy suffers from several disadvantages as significant toxicity of the prescribed drugs, poor patient compliance, and lengthy treatment periods, which result in drug resistance and MDR-TB. On the other hand, common HIV antiretroviral treatments are incompatible with the current anti- tubercular therapy because of shared drug toxicity and drug-drug interactions. Paradoxically, this global health pandemic is demanding new therapies when resources and benefits are waning. However, continued tuberculosis drug discovery is critical to address the burgeoning MDR-TB as well as global health need. Preceding anti-tubercular candidate drugs bearing oxadiazole rings are most likely to be effective against resistant strains but due to weaker activity profile than the first-line drugs, they are facing difficulties to enter for clinical trials. In order to overcome these drawbacks, there is significant need for shorter and simpler anti-tubercular drugs with improved properties such as enhanced activity against MDR-TB strains, lower cytotoxicity, and shortened treatment length, new mechanisms of action, with improved ability to penetrate host cells and exert anti-tubercular activity in the intracellular environment.

5. Cross-reference to related applications I Prior art I

[1] Bioorg. Med. Chem. Lett., 20 (2010) 746-754

[2] WO/2010/094120 A1

[3] W02008056687A1

[4] Bioorg. Med. Chem. Lett. 25 (2015) 3234-3245

[5] EP2123 652A1 , 2009

[6] Spirocyclic compounds, WO2019204354A1

[7]W02006/105442A2

[8] WO2007/128782A1

[9] W02010/027567A2

[10] W02004/092179A1

[11 ] WO 2007/011809 A1

[12] WO2012/112743A1

The main object of the present invention is to provide Tricyclic spiro[chromane-2,4'-piperidin]-4(3H)-one with 1 ,3,4-oxadiazole linkers compositions and process for preparation thereof as potent precursors of anti-tubercular agents.

Another object is to provide for compounds with inclusion of oxadiazole into the backbone of spiropiperidinyl chromanone unit to make sure that the new moiety has potent anti-tubercular properties based on a whole cell screen, under multiple physiological conditions on replicating Mtb.

Summary of invention:

The present invention provides Tricyclic spiro[chromane-2,4'-piperidin]- 4(3H)-one with 1 ,3,4-oxadiazole linkers compositions and process for preparation thereof, as potent precursors of anti-tubercular agents. The said compounds have general formula

FORMULA (X)

Wherein, independently for each occurrence:

R is H, Br

R' is OH or O

A is

Wherein B1 is Halogen, OH, OR", ON, SR" or SO2R", NHR", NHCOR", CF3, OCF3, OCHF2, an optionally substituted a straight chain, branched, or cyclic (Cl- C6)-R" wherein up to two CH2 units may be replaced with O, CO, S, SO, SO2, CF2, cycloalkyl, heterocycloalkyl, aryl, heteroaryl; B2 is OH, OR", ON, SR" or SO2R", NHR", NHCOR", CF3, OCF3, OCHF2, an optionally substituted a straight chain, branched, or cyclic (Cl- C6)-R" wherein up to two CH2 units may be replaced with O, CO, S, SO, SO2, CF2, cycloalkyl, heterocycloalkyl, aryl, heteroaryl;

B3 is Halogen, OH, OR", NO2, CN, CHO, COOR", COOH, NHR", NHCOR", CF3, OCF3, OCHF2, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, an optionally substituted a straight chain, branched, or cyclic (Cl- C6)-R" wherein up to two CH2 units may be replaced with O, CO, S, SO, SO2, CF2; B4 is OR", CN, SR" or SO2R", NHR", NHCOR", NO2, CF3, OCF3, OCHF2, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, an optionally substituted a straight chain, branched, or cyclic (Cl- C6)-R" wherein up to two CH2 units may be replaced with O, CO, S, SO, SO2, CF2;

Wherein, independently for each occurrence

R" is short chain alkyl, or an optionally substituted aryl, heteroaryl, cycloalkyl, or heterocycloalkyl;

B3 B4 is cyclic (Cl- C6)-R" wherein up to two CH2 units may be replaced with O, CO, S, SO, SO2, CF2 or NR" B3 B4 is cyclic

Tricyclic spiro[chromane-2,4'-piperidin]-4(3H)-one with 1 ,3,4-oxadiazole linkers compositions and process for preparation thereof, as potent precursors of anti-tubercular agents. (Fig. 1 , Compound [D]) Moreover extended linkers of spiro[chromane-2,4'-piperidine]-4(3/7)-one fusion with oxadiazole ring played crucial role for stearoyl-CoA desaturase (SCD-1) inhibitory activity. (Fig. 1 , Compound [B and C]) Hitherto these existing strategies never exploited amidic oxadiazole linkers to conceal the structural gap. In this context, principally extended linker of oxadiazole moiety at spiro piperidinyl (Fig 1 , Compound E) will dramatically reduce the number of free rotatable bonds and formulate the entire molecule more rigid as well as possibility to show more efficient interaction with the enzyme by means of better pharmacokinetic (PK) profile.

Fig 1-Progrees in spiropiperidinyl linked oxadiazoles Accordingly, the present invention provides Tricyclic spiro[chromane-2,4'- piperidin]-4(3H)-one with 1,3,4-oxadiazole linker having general formula X as herein below:

FORMULA X Wherein, independently for each occurrence:

R is H, Br

R ¹ is OH or O

A is

Wherein

Bi is Halogen, OH, OR", ON, SR" or SO ₂ R", NHR", NHCOR", CF ₃ , OCF ₃ , OCHF2, an optionally substituted a straight chain, branched, or cyclic (Cl- C6)-R" wherein up to two CH2 units may be replaced with O, CO, S, SO, SO2, CF2, cycloalkyl, heterocycloalkyl, aryl, heteroaryl;

B ₂ is OH, OR", CN, SR" or SO2R", NHR", NHCOR", CF ₃ , OCF ₃ , OCHF2, an optionally substituted a straight chain, branched, or cyclic (Cl- C6)-R" wherein up to two CH2 units may be replaced with O, CO, S, SO, SO2, CF2, cycloalkyl, heterocycloalkyl, aryl, heteroaryl;

B ₃ is Halogen, OH, OR", NO2, CN, CHO, COOR", COOH, NHR", NHCOR", CF ₃ , OCF ₃ , OCHF2, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, an optionally substituted a straight chain, branched, or cyclic (Cl- C6)-R" wherein up to two CH2 units may be replaced with O, CO, S, SO, SO2, CF2;

B4 is OR", CN, SR" or SO2R", NHR", NHCOR", NO2, CF ₃ , OCF ₃ , OCHF2, cycloalkyl, heterocycloalkyl, aryl, heteroaryl, an optionally substituted a straight chain, branched, or cyclic (Cl- C6)-R" wherein up to two CH2 units may be replaced with O, CO, S, SO, SO2, CF2;

Wherein, independently for each occurrence

R" is short chain alkyl, or an optionally substituted aryl, heteroaryl, cycloalkyl, orheterocycloalkyl;

B ₃ B ₄ is cyclic (Cl- C6)-R" wherein up to two CH2 units may be replaced with O, CO, S, SO, SO2, CF ₂ or NR" characterised by the synthesis of consigned derivatives of various substituted, spiro[chroman-2,4'-piperidin]-4(3/7)-ones.

The invention provides a general process for the preparation of the said compounds which comprises treating appropriate 2-hydroxyacetophenones I via Kabbe multi-component cyclo-condensation reaction with Boc- protected 4-pipyridinone II, subjecting the N-Boc protected compounds III to deprotection through acidic hydrolysis using the trifluro acetic acid (TFA), phosphoric acid, hydrochloric acid, hydrobromic acid, iodine, copper triflet to yield respective amine derivatives IV, treating unpurified compounds IV with ethyl chloro/bromo acetate in tetra hydro furan (THF) in presence of inorganic base such as sodium carbonate, potassium carbonate, caesium carbonate, sodium hydride, sodium tertiary butoxide, potassium tertiary butoxide, sodium hydroxide, potassium hydroxide, lithium hydroxide, magnesium hydroxide, caesium hydroxide, sodium acetate, potassium acetate or organic amines such as triethyl amine, diisopropyl ethyl amine, pyridine, N,N-dimethyl amino pyridine, guanidine to obtain the formations of V, subjecting the formation of V to column purification in ethyl acetatehexane to obtain yellow coloured viscous liquid, further treating directly the formation of V with hydrazine hydrate to obtain formation of a complex mixture, which is explained by the existence of additional carbonyl group from the ketonic functionality at chromanones, inhibiting the standard order of reaction, Thus, we altered new approach in our subsequent attempt.

Scheme 1

Wherein, independently for each occurrence:

R is H or Br, Y is tertiary butyloxy carbonyl

Ri is Ethyl

To probe possible reasons for low conversions noted in Scheme 1 , the reduction of V was performed using sodium borohydride in ethanol and subsequent treatment of ethyl esters (VI) with hydrazine hydrate gives key intermediate hydrazides (VII). (Scheme 2) Further the condensation and intramolecular oxidative cyclization of compounds VII with equimolar quantities of aldehyde in ethanokwater (50:50) mixture at 90-100 °C catalysed by sodium bisulphate, I2/K2CO3, 2-iodoxybenzoic acid/tetraethylammonium bromide, iodosobenzene diacetate, iodosobenzene bis(trifluoroacetate) yielded corresponding oxadiazole derivatives. The semiaqueous conditions and mild temperature are rather best fit among alternative cyclization approaches to oxadiazoles. With a workable synthesis in hand, we turned our attention toward the development of a more efficient approach for the library synthesis of ((1 ,3,4-oxadiazol-2- yl)methyl) spiro[chromane-2,4'-piperidin]-4(3/7)-ols (IX) among diverse aldehydes VIII. Finally, oxidation of IX was carried out using IBX (2- lodoxybenzoic acid) in DMSO at room temperature. The targeted oxadiazoles X were obtained in moderate to good yields.

Scheme 2

Wherein, independently for each occurrence:

R is H or Br,

Ri is Ethyl Bi is Cl, OMe

B2 is OH, OMe,

B ₃ is Br, Cl, OH, OMe, NO2,

B4 is OMe,

B3 B4 is cyclic; All the synthesized spiro[chroman-2,4'-piperidin]-4-ol/one derivatives were fully characterised by spectral technique and screened for their in vitro anti tubercular activity against Mycobacterium tuberculosis H37 Rv ATCC 25177 using BD Bactec MGIT 320, a fully automatic system.

The following examples describe the process of the present invention in details which are illustrative only and should not be construed to limit the scope of the present invention in any manner.

Starting from commercially available 2-hydroxyacetophenones (I), the novel tricyclic spiroketone IX-X was successfully synthesized in seven steps overall good to moderate yields.

Following compounds were prepared under the invention.

[IXbe] [IXbf]

Examples

General comments Unless otherwise stated all reagents and solvents were purchased from commercial sources and used without further purification. Analytical thin layer chromatography (TLC) was performed on precoated silica gel 60F 254 plates and spots were visualized under UV light. For flash column chromatography, silica gel (Merck, grade 9385, 230-400mesh) was used. Melting points are uncorrected. All the listed new compounds were fully characterized by IR, ¹ H NMR, ¹³ CNMR, and HRMS, and the purity was higher than 95% as assessed byLC/MS. IR spectra (KBr disks) were recorded using a Perkin-Elmer 237 spectrophotometer. ¹ H NMR and ¹³ C NMR spectra were recorded in CDCh orDMSO-d6 on a Bruker 400 MHz spectrometer. They are reported in parts per million on the 5 scale from TMS. Coupling constants (J) are reported in Hz and the splitting abbreviations used are: s, singlet; d, doublet; t, triplet; q, quartet; m, multiplet; comp, overlapping multiplets of magnetically nonequivalent protons; br, broad. LC/MS was performed on a Waters Xevo-TQD LCMSMS.

General procedure for synthesis of 4-oxospiro[chromane-2,4'- piperidine]tert-butyl-4-oxospiro[chromane-2,4'-piperidine]-T -carboxylate (HI)

To a stirred solution of 2-hydroxybenzoic acid (6g, 43.44mmol) in 40ml methanol was added pyrrolidine (3.15g, 44.31 mmol) and stirred at room temperature for 5-10min. To the above solution was added tert-butyl 4- oxopiperidine-1-carboxylate (8.83g, 44.31 mmol) in 15ml methanol. The reaction mixture was stirred at RT for 16h. After completion of stirring, methanol was evaporated under vacuum and compound was purified by silica gel column chromatography eluting with 0-10% EtOAc in n-hexane to afford 11gm of tert-butyl 4-oxospiro[chromane-2,4'-piperidine]-1'- carboxylate as an off-white solid. tert-butyl 4-oxospiro[chromane-2,4'-piperidine]-1'-carboxylate (Illa) Boc

¹ H NMR (400 MHZ,CDCI ₃ ) 6 7.71 (d, J = 8.4 Hz, 1 H), 7.20 (d, J = 1.8 Hz, 1 H), 7.14 (dd, J = 8.4, 1.8 Hz, 1 H), 3.95 - 3.78 (m, 2H), 3.19 (t, J = 12.1 Hz, 2H), 2.69 (s, 2H), 1.99 (d, J = 12.7 Hz, 2H), 1.66 - 1.53 (m, 2H), 1.45 (s, 9H).

M.P.: 77-79 °C tert-butyl 7-bromo-4-oxospiro[chromane-2,4'-piperidine]-1'-carboxylate: (lllb)

¹ HNMR (400 MHz, CDCI3) 5 7.71 (d, J = 8.4 Hz, 1 H), 7.20 (d, J = 1.8 Hz, 1 H), 7.14 (dd, J = 8.4, 1.8 Hz, 2H), 3.95 - 3.78 (m, 2H), 3.19 (t, J = 12.1 Hz, 2H), 2.69 (s, 2H), 1.99 (d, J = 12.7 Hz, 2H), 1.66 - 1.53 (m, 2H), 1.45 (s, 9H).

General procedure for Boc deprotection: (IV)

To a stirred solution of tert-butyl 4-oxospiro[chroman-2,4'-piperidine]-1'- carboxylate (11g) in DCM (100-120ml) was added TFA (31.6g) drop wise at 0 °C under N2 atmosphere. Then the reaction mixture was allowed to stir at room temperature for 16h. After completion, reaction mixture was concentrated under reduced pressure. Water was added to the residue and basified with 5N NaOH solution. The product was extracted with DCM, dried over Na2SC>4, filtered, and concentrated under vacuum to get 7.8g of desired compound. Without further purification it was subjected for next step. spiro[chromane-2,4'-piperidin]-4-one: (I a)

¹ HNMR (400 MHz, DMSO-D6) 57.72 (dd, J= 7.8, 1.7 Hz, 1H), 7.63-7.51 (m, 1H), 7.18-6.93 (m, 2H), 4.10 (s, 1H), 2.96-2.76 (m, 6H), 1.86 (d, J = 13.3 Hz, 2H), 1.72-1.57 (m, 2H).

7-bromospiro[chromane-2,4'-piperidin]-4-one: (IVb)

¹ HNMR (400 MHz, DMSO-D6) 57.59 (d, J = 8.3 Hz, 1H), 7.30 (d, J= 1.8 Hz, 1H), 7.19 (dd, J= 8.3, 1.8 Hz, 1H), 4.05 (s, 1H), 2.86 -2.73 (m, 4H), 2.72-2.60 (m, 2H), 1.75 (d, J= 13.4 Hz, 2H), 1.65-1.47 (m, 2H).

General procedure for /V-protection: (V)

To a stirred solution of spiro[chromane-2,4'-piperidin]-4-one (7.8g, 35.9mmol) in THF (125 mL) was added Na2COs (5.71g, 53.85mmol) and ethyl bromoacetate (6.59, 39.49mmol) The mixture was stirred at room temperature for 24 h. After completion of the reaction, it was poured into water (100 mL), and the mixture was extracted with EtOAc. The solvent was evaporated under reduced pressure. The mixture was purified by column chromatography (silica gel, 100% CH2CI2) to afford 7.5g thick yellowish oil.

Ethyl 2-(4-oxospiro[chromane-2,4'-piperidin]-1'-yl)acetate: (Va)

¹ HNMR (400 MHz, CDCI3) 57.86-7.83 (m, 1H), 7.47 (ddd, J =8.0, 7.4, 1.8 Hz, 1H), 7.01 -6.95 (m, 2H), 2.05 (dd, J= 13.5, 11.0 Hz, 2H), 1.93-1.79 (m), 1.27 (t, J= 7.1 Hz). Ethyl2-(7-bromo-4-oxospiro[chromane-2,4'-piperidin]-T-yl)ace tate: (Vb)

¹ HNMR (400 MHz, CDCI3) 5 7.51 (d, J = 8.4 Hz, 1 H), 7.01 (d, J = 1.8 Hz, 1 H), 6.93 (dd, J = 8.4, 1.8 Hz, 1 H), 4.00 (q, J = 7.1 Hz, 2H), 3.06 (s, 2H), 2.54 (dt, J = 11.3, 3.6 Hz, 2H), 2.41 (td, J = 11 .5, 2.6 Hz, 2H), 1.84 (dd, J = 14.5, 2.5 Hz, 2H), 1.71 - 1.56 (m, 2H), 1.08 (t, J = 7.1 Hz, 3H).-

General procedure for ketone reduction: (VI)

To a stirred solution of Ethyl 2-(4-oxospiro[chromane-2,4'-piperidin]-1'- yl)acetate (9.12g, 30.06mmol) in 100ml ethanol was added NaBH4 (1.14g, 30.06mmol) at 0 °C. The reaction mixture was stirred at same temperature for 1 h and then slowly allowed to be stirred at RT for 8-12h. The reaction mixture was cooled to 0 °C and quenched with aq. NH4CI solution. The solvent was evaporated under reduced pressure and residue was extracted with EtOAc, dried over sodium sulphate, filtered, and concentrated under vacuum to afford 8.5g colourless to light yellow oil.

Ethyl 2-(4-hydroxyspiro[chromane-2,4'-piperidin]-1'-yl)acetate: (Via)

¹ HNMR (400 MHz, DMSO-D6) 5 7.35 (d, J = 6.8 Hz, 1 H), 7.16 - 7.01 (m, 1 H), 6.82 (td, J = 7.4, 1.2 Hz, 1 H), 6.68 (dd, J = 8.1 , 1.1 Hz, 1 H), 5.27 (d, J = 6.2 Hz, 1 H), 4.63 (dd, J = 15.0, 6.2 Hz, 1 H), 4.05 (q, J = 7.1 Hz, 2H), 3.18 (s, 2H), 2.55 (dd, J = 11 .7, 8.1 Hz, 3H), 2.44 - 2.35 (m, 1 H), 2.03 (dd, J = 13.4, 6.1 Hz, 1 H), 1.82 - 1.48 (m, 3H), 1.16 (t, J = 7.1 Hz, 3H). Ethyl 2-(7-bromo-4-hydroxyspiro[chromane-2,4'-piperidin]-T-yl)acet ate:

(Vlb)

¹ HNMR (400 MHz, DMSO-D6) 6 7.32 - 7.28 (m, 1 H), 7.02 (dd, J = 8.2, 2.0 Hz, 1 H), 6.89 (d, J = 1.9 Hz, 1 H), 5.42 (d, J = 5.9 Hz, 1 H), 4.60 (dt, J = 11.7, 6.0 Hz, 1 H), 4.06 (q, J = 7.1 Hz, 2H), 3.22 (s, 2H), 3.13 (s, 1 H), 2.59 (s, 3H), 2.05 (dd, J = 13.5, 6.1 Hz, 1 H), 1.80 - 1.58 (m, 5H), 1.16 (t, J = 7.1 Hz, 3H).

General procedure for hydrazide formation: (VII)

To a stirred solution of ethyl 2-(4-hydroxyspiro[chromane-2,4'-piperidin]-1'- yl)acetate (8.5g, 30.87mmol) in methanol (100ml) was added 35% hydrazine hydrate (17.66g, 123.50mmol) and reaction mixture refluxed for 12-16h. After completion reaction mixture was concentrated under reduced pressure. The residue was extracted with DCM, dried over sodium sulphate, filtered, and concentrated under reduced pressure to afford 5.2g yellowish sticky solid. Without further purification it was proceed for next step.

2-(4-hydroxy-3,4-dihydro-1'H-spiro[chromene-2,4'-piperidi n]-T- yl)acetohydrazide (Vila)

2-(7-bromo-4-hydroxy-3,4-dihydro-TH-spiro[chromene-2,4'-p iperidin]-1'-yl) acetohydrazide (VI lb) ¹ H NMR (400 MHz,DMSO-D6 ) 6 8.83 (s, 1 H), 7.33 - 7.26 (m, 1 H), 7.01 (dd, J = 8.2, 2.0 Hz, 1 H), 6.90 (d, J = 2.0 Hz, 1 H), 5.40 (d, J = 6.1 Hz, 1 H), 4.59 (dt, J = 8.9, 6.1 Hz, 1 H), 4.17 (s, 2H), 2.89 (s, 2H), 2.62 - 2.49 (m, 2H), 2.45 - 2.27 (m, 2H), 2.02 (dd, J = 13.5, 6.1 Hz, 1 H), 1.69 (m, 5H).

General procedure for oxadiazole formation: (IX)

To a stirred solution of 4-oxospiro[chromane-2,4'-piperidine]-1'- carbohydrazide (0.81 mmol) in ethanol: water (9ml, 1 :2), was added aldehyde (a-n) (0.81 mmol) and NaHSOs (1.62mmol). The reaction mixture was heated at 90-100 °C for 12-16h. The reaction mixture was poured over crushed ice and stirred for 30min. The precipitate was filtered, washed with cold ethanol: water (1 :1) to afford a desired compound.

1) 1'-((5-(2-chlorophenyl)-1 ,3,4-oxadiazol-2-yl)methyl)spiro[chromane- 2,4'-piperidin]-4-ol: [IXaa]

IR:3213.0, 3063.2, 2922.2, 2858.9, 1684.8, 1580.4, 1457.5, 1230.0, 1118.2, 1028.7, 752.9cm- ¹ .

¹ H NMR (400 MHz, DMSO-D6) 5 7.52 (dd, J = 6.9, 2.0 Hz, 1 H), 7.43 (dd, J = 6.7, 2.2 Hz, 1 H), 7.37 - 7.25 (m, 2H), 7.22 - 7.14 (m, 2H), 7.01 (td, J = 7.5, 1.4 Hz, 1 H), 6.95 - 6.85 (m, 1 H), 4.75 (t, J = 8.0 Hz, 1 H), 3.66 (s, 2H), 2.77-2.50 (m, 3H), 2.37-2.26 (m, 1 H), 2.09-1.98 m,1 H), 1.76-1.62 (m, 5H). ¹³ CNMR (100 MHz, DMSO-D6) 5 184.8, 168.0, 166.5, 158.7, 152.3, 144.3, 141.0, 134.0, 133.8, 132.5, 131.5, 130.1 , 129.8, 128.7, 127.5, 126.9, 1z25.9, 120.4, 116.8, 9,4.8, 72.9, 67.8, 61.5, 60.8, 57.5, 49.4, 38.4, 35.9, 33.3, 32.7, 30.2, 29.5, 28.8, 23.6, 22.8, 14.1 , 11.0 MP.: 76-78 °C.

Molecular Formula = C22H22CIN3O3

Formula Weight = 411.88 2) 1'-((5-(4-hydroxy-3-methoxyphenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-ol: [IXai]

IR: 3190.6, 3037.8, 2952.1 , 1684.8, 1587.8, 1513.3, 1162.9, 1222.6, 1118.2, 984.0, 752.9 cm- ¹ .

¹ H NMR (400 MHz, DMSO-D6) 5 9.99 - 9.81 (m, 1 H), 7.50 (dd, J = 13.4, 8.7 Hz, 2H), 7.35 (d, J = 8.2 Hz, 1 H), 7.19 (s, 1 H), 7.07 (dt, J = 8.2, 2.3 Hz, 1 H), 6.86 - 6.77 (m, 2H), 5.46 (t, J = 6.5 Hz, 1 H), 4.65 (d, J = 5.7 Hz, 1 H), 3.88 (s, 3H), 3.54 (s, 2H), 2.82 - 2.54 (m, 3H), 2.49 - 2.24 (m, 1 H), 2.09 (dd, J = 13.3, 6.1 Hz, 1 H), 1.75 (m, 5H).

¹³ CNMR (100 MHz, DMSO-D6) 5174.3, 161.0, 158.0, 149.8, 147.9, 135.7, 128.8, 125.3, 124.0, 117.0, 115.4, 109.2, 71.1 , 61.4, 55.9

M.P.: 162-164 °C

Molecular Formula = C23H25N3O5

Formula Weight = 423.46

3) 7-bromo-1'-((5-(2-chlorophenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-ol: [IXba]

IR:3220.4, 2963.2, 2825.3, 1684.8, 1595.3, 1476.0, 1259.8, 1028.7, 797.7cm- ¹ .

¹ HNMR (400 MHz, DMSO-D6) 5 8.06 - 7.64 (m, 1 H), 7.57 - 7.17 (m, 4H), 7.17 - 6.88 (m, 2H), 5.48 (m, 1 H), 4.66 (s, 1 H), 3.44 (d, J = 6.6 Hz, 2H), 3.20 (m, 3H), 2.67 (s, 1 H), 2.26 - 1.58 (m, 6H).

¹³ CNMR (100 MHz, DMSO-D6) 5 166.3, 153.3, 144.4, 141.0, 134.0, 133.8, 131.5, 130.2129.9, 128.9, 127.5, 126.9, 125.4, 1123.3, 121.7, 119.9, 78.9, 61.1 , 60.7, 50.6, 49.2, 35.8, 34.8, 33.3, 32.8, 13.5 MP.: 128-140 °C Molecular Formula = C22H2iBrCIN3C>3

Formula Weight = 490.77

4) 7-bromo-1'-((5-(4-chlorophenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-ol: [IXbb]

IR: 3104.9, 2937.1 , 2825.3, 1703.4, 1595.3, 1401.5, 1248.7, 1120.7, 972.8, 816.3cm- ¹ .

¹ HNMR (400 MHz, DMSO-D6) 5 7.65 (dd, J = 11.4, 4.8 Hz, 2H), 7.51 - 7.41 (m, 2H), 7.30 (d, J = 8.3 Hz, 1 H), 6.98 (m, 2H), 5.41 (dd, J = 8.8, 4.4 Hz, 1 H), 4.61 (s, 1 H), 3.17 - 3.11 (m, 2H), 2.76 - 2.51 (m, 3H), 2.45 - 2.31 (m, 1 H), 2.13 - 1.99 (m, 1 H), 1.86 - 1.58 (m, 5H).

¹³ CNMR (100 MHz, DMSO-D6) 5 171.5, 166.6, 153.5, 146.6, 141.9, 135.1 ,

133.1 , 130.0, 129.1 , 128.9, 128.3, 125.7, 125.6, 123.0, 121.0, 119.7, 74.3,

61.1 , 58.3, 46.3, 36.3, 33.6.

M.P.:165-167 °C

Mol. Formula = C22H2iBrCIN3C>3

Formula Weight = 490.77

5) 7-bromo-1 '-((5-(4-bromophenyl)-1 ,3,4-oxadiazol-2-yl)methyl)spiro[chromane-

2,4'-piperidin]-4-ol: [IXbc]

IR: 3108.6, 2970.7, 2825.3, 1703.4, 1595.3, 1405.2, 1282.4, 1252.4, 1125.7, 972.8, 816.3cm- ¹ .

¹ H NMR (400 MHz, CDCI3) 5 7.62 (d, J = 3.9 Hz, 4H), 7.34 (d, J = 8.2 Hz, 1 H), 7.06 (dd, J = 8.2, 1.7 Hz, 1 H), 6.95 (d, J = 1 .8 Hz, 1 H), 5.45 (dd, J = 6.0, 3.6 Hz, 1 H), 4.65 (dd, J = 13.5, 6.6 Hz, 1 H), 3.57 (s, 2H), 2.91 - 2.55 (m, 3H), 2.38 (dd, J= 14.2, 7.7 Hz, 1 H), 2.09 (dd, J = 14.6, 7.0 Hz, 1 H), 1.90 - 1.59 (m, 5H).

¹³ CNMR (100 MHz, DMSO-D6) 5 179.5, '72.0, 166.6, 153.5, 146.8, 142.0, 133.5, 131.7, 130.0, 129.9, 128.4, 123.4, 124.1 , 123.4, 122.9, 121.1 , 119.6, 61.2, 58.3, 49.3, 36.4, 33.6 MP.: 198-200 °C

Molecular Formula = C22H2iBr2N30s

Formula Weight = 535.22

6) 7-bromo-1 '-((5-(4-nitrophenyl)-1 ,3,4-oxadiazol-2-yl)methyl)spiro[chromane-

2,4'-piperidin]-4-ol: [IXbd]

IR: 3369.5, 3045.9, 2922.2, 1686.8, 1599.0, 1513.3, 1341.8, 1218.8, 1092.5, 808.8cm- ¹ .

¹ HNMR (400 MHz, ) 5 8.28 (m, 2H), 8.01 - 7.83 (m, 2H), 7.42 (d, J = 8.4 Hz, 1 H), 7.12 - 6.99 (m, 2H), 5.52 (s, 1 H), 4.52 (s, 1 H), 3.40 (s, 2H), 2.60 (s, 1 H), 2.22 - 1.60 (m, 8H).

¹³ C NMR (100 MHz, DMSO-D6) 5 152.8, 152.6, 148.2, 143.1 , 140.1 , 130.7, 1283, 128.1 , 124.0, 123.9, 123.6, 121.2, 121.1 , 119.7, 116.2, 60.8, 49.1.

MP: 191-193 °C

Molecular Formula = C22H2iBrN40s

Formula Weight = 501.33

8) 7-bromo-1'-((5-(4-hydroxyphenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-ol: [IXbe] IR: 3242.8, 2948.3, 2825.3, 1662.4, 1599.0, 1228.3, 1118.2, 1021.3, 950.5, 805.1cm- ¹ .

¹ H NMR (400 MHz, DMSO-D6) 59.88 (d, J= 15.6 Hz, 1H), 7.50 (dd, J =

13.4, 8.7 Hz, 2H), 7.35 (d, J = 8.2 Hz, 1H), 7.07 (dt, J= 8.2, 2.3 Hz, 1H), 6.96 (d, J = 2.0 Hz, 1 H), 6.85 - 6.75 (m, 2H), 5.46 (t, J = 6.5 Hz, 1 H), 4.65 (d, J= 5.7 Hz, 1H), 2.77-2.53 (m, 5H), 2.50-2.31 (m, 2H), 2.16-2.01 (m, 1H), 1.88-1.63 (m, 5H).

¹³ CNMR (100 MHz, DMSO-D6) 5170.7, 166.2, 159.8, 153.5, 148.5, 144.4, 130.0, 129.2, 128.5, 125.4, 123.1, 121.1, 119.5, 115.8, 74.2, 61.1, 58.4,

49.4, 39.2, 33.5

M.P.: 170-172 °C

Molecular Formula = C22H22BrNsO4

Formula Weight = 472.33

9) 7-bromo-1'-((5-(4-methoxyphenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-ol: [IXbf]

IR:3175.7, 3093.7, 2963.2, 2829.0, 1654.9, 1602.8, 1408.9, 1241.2, 1166.7, 1121.9, 984.0, 924.4, 760.4cm- ¹ .

¹ H NMR (400 MHz, DMSO-D6) 57.51 (dd, J= 13.4, 8.7 Hz, 2H), 7.37 (d, J = 8.2 Hz, 1H), 7.08 (dt, J = 8.2, 2.3 Hz, 1H), 6.97 (d, J = 2.0 Hz, 1H), 6.90 - 6.78 (m, 2H), 5.48 (t, J = 6.5 Hz, 1 H), 4.67 (d, J = 5.7 Hz, 1 H), 3.80 (s, 3H), 3.56 (s, 2H), 2.66 (m, 3H), 2.49-2.37 (m, 1H), 2.11 (dd, J= 13.3, 6.1 Hz, 1H), 1.77 (m, 5H).

¹³ CNMR (100 MHz, DMSO-D6) 5171.3, 166.3, 161.2, 160.8, 153.6, 148.0, 143.2, 130.0, 129.9, 128.4, 127.1, 126.6, 125.5, 123.0, 122.9, 121.0, 119.5,

114.1, 74.4, 61.1, 58.3, 55.3, 36.4, 33.5

MP.: 128-130 °C

Molecular Formula = C23H24BrNsO4

Formula Weight = 486.35 10) 4-(5-((7-bromo-4-hydroxyspiro[chromane-2,4'-piperidin]-1'-yl )methyl)-

1,3,4-oxa- diazol-2-yl)benzene-1,2-diol: [IXbg]

IR: 3485.1, 3231.6, 2944.6, 2825.3, 1640.0, 1595.3, 1524.5, 1446.2,

1278.5, 1222.6, 1118.2, 980.3, 805.1cm- ¹ .

¹ HNMR (400 MHz,DMSO-D6) 59.30 (s, 1 H), 9.16 (bd, 1 H), 7.30 (d, J = 8.3 Hz, 1H), 7.19-6.99 (m, 2H), 6.91 (d, J= 1.9 Hz, 1H), 6.85 (dd, J = 8.2, 1.9 Hz, 1H), 6.72 (dd, J = 8.1, 3.8 Hz, 1H), 5.42 (d, J=6.1 Hz, 1H), 4.61 (dt, J = 12.0, 5.9 Hz, 1 H), 3.48 (s, 2H), 2.80 - 2.50 (m, 3H), 2.44 - 2.28 (m, 1 H), 2.14-1.99 (m, 1H), 1.86-1.55 (m, 5H).

¹³ CNMR (100 MHz, DMSO-D6) 5165.9, 153.5, 148.6, 147.6, 145.6, 144.2, 130.0, 126.1,125.7, 123.0, 121.0, 120. 5115.5, 113.6, 74.1, 61.1, 49.3,

8119.5, 36.2, 33.

M.P. : 146-148 °C.

Molecular Formula = C22H22BrN30s

Formula Weight = 488.34

11)7-bromo-T-((5-(3-hydroxy-4-methoxyphenyl)-1,3,4-oxadia zol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-ol:[ IXbh]

IR: 3201.8, 2963.2, 2840.2, 1654.9, 1595.3, 1442.5, 1222.5, 1129.4,

995.2, 734.3cm- ¹ .

¹ HNMR (400 MHz, DMSO-D6) 59.20 (bd, 1H), 7.31 (dd, J = 8.3, 3.7 Hz, 1H), 7.17 (d, J = 1.6 Hz, 1H), 7.12-6.85 (m, 4H), 4.71-4.55 (m, 1H), 4.05 (q, J = 5.2 Hz, 1 H), 3.77 (d, J = 4.5 Hz, 3H), 3.13 (d, J = 5.2 Hz, 2H), 2.78 - 2.49 (m, 3H), 2.45 - 2.26 (m, 1 H), 2.09-2.01 (m, 1 H), 1 .94 - 1.46 (m, 5H). ¹³ CNMR (100 MHz, DMSO-D6) 5 166.6, 152.7, 150.1 , 146.9, 141.8, 130.6,

126.9, 125.2, 123.7, 121.2, 120.7, 119.8, 113.2, 112.7, 111.3, 72.160.9,

56.9, 55.8, 49.1 , 31.8, 18.5 M.P.: 76-78 °C

Molecular Formula = C23H24BrN30s

Formula Weight = 502.34

12) 7-bromo-1'-((5-(4-hydroxy-3-methoxyphenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro [chromane-2,4'-piperidin]-4-ol:[ IXbi]

IR: 3213.0, 2969.2, 1634.8, 1595.3, 1408.3, 1248.8, 1025.0, 797.7cm- ¹ .

¹ HNMR (400 MHz, DMSO-D6) 5 9.48 (s, 1 H), 7.12 (m, 5H), 6.79 (s, 1 H), 5.47 (bd, J = 31.6 Hz, 1 H), 4.62 (s, 1 H), 3.78 (s, 3H), 3.40 (s, 2H), 3.09 (s, 2H), 2.60 (s, 2H), 2.16 - 1.59 (m, 6H).

¹³ CNMR (100 MHz, DMSO-D6) 5 168.0, 165.2, 149.3, 148.9, 145.8, 130.6, 125.7, 123.4, 122.7, 121.7, 120.92, 119.6, 115.7113.4, 109.8, 74.0, 73.1 ,

60.9, 56.9, 55.9, 49.0, 35.4, 34.133.0 M.P.: 156-158 °C

Molecular Formula = C23H24BrN30s

Formula Weight = 502.34

13) 7-bromo-1'-((5-(3,4-dimethoxyphenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-ol: [IXbk] IR:3388.2, 2928.2, 2832.8, 1669.8, 1595.3, 1505.8, 1267.3, 1226.3,

1162.9, 1125.7, 1021.3, 976.6, 805.1cm- ¹ .

¹ HNMR (400 MHz, DMSO-D6) 57.31 (d, J= 8.2 Hz, 1H), 7.23 (d, J= 10.8 Hz, 1H), 7.12 (d, J= 8.1 Hz, 1H), 7.03 (d, J = 8.2 Hz, 1H), 6.98 (d, J = 8.2 Hz, 1H), 6.92 (s, 1H), 5.42 (d, J = 6.1 Hz, 1H), 4.61 (dd, J= 13.3, 7.0 Hz, 1H), 3.76 (s, 6H), 3.66 (s, 2H), 2.79-2.50 (m, 3H), 2.41-2.32 (m, 1H), 2.05 (dd, J = 13.4, 6.0 Hz, 1H), 1.87-1.55 (m, 5H).

¹³ CNMR (100 MHz, DMSO-D6) 5166.21 , 153.1, 151.4, 149.4, 148.8, 129.5, 126.4, 123.9, 123.6, 122.8 122.3, 120.3, 110.4, 108.3, 73.3, 62.5, 60.9, 56.1, 55.9, 49.5, 41.3, 35.9, 34.2.

MP: 77-79 °C.

Molecular Formula = C24H26BrN30s

Formula Weight = 516.38

14) 7-bromo-1'-((5-(3,4,5-trimethoxyphenyl)-1 ,3,4-oxadiazol-2-yl)methyl)spiro- [chrom ane-2,4'-piperidin]-4-ol : [IXbl]

IR: 3377.0, 2937.1, 2829.0, 1673.6, 1576.7, 1498.4, 1416.4, 1326.9, 1226.3, 1121.9, 998.9, 920.7, 808.8cm- ¹ .

¹ H NMR (400 MHz, DMSO-D6) 57.31 (d, J= 8.3 Hz, 1H), 7.03 (dd, J= 8.2, 1.9 Hz, 1H), 6.96-6.87 (m, 3H), 5.42 (d, J= 6.1 Hz, 1H), 4.66-4.56 (m, 1 H), 3.78 (s, 3H), 3.66 (s, 3H), 3.55 (s, 2H), 2.85 - 2.49 (m, 3H), 2.44 - 2.30 (m, 1H), 2.05 (dd, J= 13.5, 6.1 Hz, 1H), 1.87- 1.60 (m, 5H).

¹³ C NMR (100 MHz, DMSO-D6) 5153.4, 153.1, 148.8, 140.2, 129.5, 128.9,

123.9, 123.5, 122.4, 120.3, 104.8, 73.2, 62.5, 60.9, 56.2, 49.5, 49.4, 41.3,

35.9, 34.2.

MP: 93-95 °C.

Molecular Formula = C25H28BrN30e

Formula Weight = 546.41 15) 7-Bromo-1'-((5-(naphthalen-2-yl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-ol; [IXbn]

IR: 3421.7, 3276.3, 2929.7, 2832.8, 1684.8, 1628.1 , 1593.3, 1538.6, 1479.8, 1177.8, 1118.2, 1028.7, 976.6, 924.4, 853.6cm- ¹ .

¹ H NMR (400 MHz, DMSO-D6) 5 8.44 (s, 1 H), 8.12 - 8.05 (m, 2H), 7.84 (m, 3H), 7.34 (d, J = 1.7 Hz, 1 H), 7.26 (ddd, J = 10.9, 5.7, 2.7 Hz, 3H), 5.45 (dd, J = 6.0, 3.6 Hz, 1 H), 4.65 (dd, J = 13.5, 6.6 Hz, 1 H), 3.57 (s, 2H), 2.91 - 2.55 (m, 3H), 2.38 (dd, J = 14.2, 7.7 Hz, 1 H), 2.09 (dd, J = 14.6, 7.0 Hz, 1 H), 1.90 - 1.59 (m, 5H).

¹³ C NMR (100 MHz, DMSO-D6) 5 166.4, 158.5, 148.2, 135.5, 130.1 , 129.9, 129.7, 128.7, 128.3, 127.4, 125.6, 123.9, 123.2, 123.0, 121.0, 119.5, 119.5, 119.3, 106.2, 74.2, 61.2, 58.2, 55.4, 49.3, 36.2, 33.5.

M.P.: 135-137 °C

Molecular Formula = C26H24BrN3C>3

Formula Weight = 506.39

General procedure for oxidation: (X)

To a stirred solution of 1'-((5-aryl-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-ol (1eq) in DMSO it was added IBX (1.6eq) and stirred at rt for 3-4h. After completion of reaction, it was added ice cold water and extracted with DCM. The organic layer dried over sodium sulphate, filtered and concentrated under reduced pressure to afford crude compound, which was purified by silica gel column chromatography eluting with MeOH:DCM (0-5%).

16) 1 '-((5-(2-chlorophenyl)-1 ,3,4-oxadiazol-2-yl)methyl)spiro[chromane-2,4'- piperidin]-4-one: [Xab]

IR: 2959.5, 2926.0, 2958.9, 1606.5, 1561.5, 1561.8, 1442.5, 1341.8, 741.7cm- ¹ .

¹ H NMR (400 MHz, CDCI3) 5 7.79 (ddd, J = 7.0, 5.2, 1.7 Hz, 1 H), 7.59 (d, J = 4.6 Hz, 1 H), 7.47 - 7.37 (m, 2H), 7.06 (dd, J = 8.3, 1 .9 Hz, 1 H), 6.99 - 6.89 (m, 2H), 6.80 (d, J = 8.3 Hz, 1 H), 3.57 (s, 2H), 2.73 - 2.61 (m, 6H), 2.03 (dd, J = 28.1 , 12.7 Hz, 2H), 1.87 - 1.72 (m, 2H).

¹³ CNMR (100 MHz, DMSO-D6) 5 175.7, 158.8, 155.3, 134.4, 131.6, 131.3, 130.6, 130.3, 128.8, 126.4, 120.7, 84.0, 67.7, 30.1 , 28.8, 22.8, 14.2, 11.1.

MP: 129-131 °C

Molecular Formula = C22H20CIN3O3

Formula Weight = 409.86

17) 1'-((5-(4-bromophenyl)-1 ,3,4-oxadiazol-2-yl)methyl)spiro[chromane- 2,4'-piperidin]-4-one: [Xac]

IR: 2937.1 , 2825.3, 1684.8, 1602.8, 1561.8, 1461.1 , 1341.8, 1230.0,

750.4, 693.3cm- ¹ .

¹ H NMR (400 MHz, CDCI3) 5 8.01 (d, J = 8.5 Hz, 1 H), 7.78 (d, J = 8.5 Hz, 2H), 7.59 - 7.55 (m, 1 H), 7.45 (d, J = 8.5 Hz, 2H), 7.17 (d, J = 1.9 Hz, 1 H), 7.13 (dd, J = 8.5, 1.9 Hz, 1 H), 3.52 (s, 2H), 2.96 (s, 2H), 2.76 (d, J = 11.5 Hz, 2H), 2.64 (dd, J = 11 .0, 8.5 Hz, 2H), 1 .98 (d, J = 12.7 Hz, 2H), 1 .89 - 1.79 (m, 2H).

¹³ CNMR (100 MHz, DMSO-D6) 5 191.5, 168.5, 166.4, 160.8, 159.0, 146.9,

142.4, 136.3, 134.3, 132.0, 131.8, 130.3, 128.5, 126.2, 123.5, 120.7, 118.4, 60.9, 57.9, 49.0, 47.7, 33.9.

MP: 122-124 °C Molecular Formula = C22H2oBrN3C>3

Formula Weight = 454.31

18) 1'-((5-(4-nitrophenyl)-1 ,3,4-oxadiazol-2-yl)methyl)spiro[chromane-2,4'- piperidin]-4-one:

IR: 2926.0, 2855.1 , 1684.8, 1602.8, 1502.1 , 1461.1 , 1300.8, 1341.8, 1110.7, 741.7, 693.3cm- ¹ .

¹ H NMR (400 MHz, CDCI3) 5 8.26 (d, J = 8.9 Hz, 2H), 8.02 - 7.80 (m, 3H), 7.60 - 7.43 (m, 1 H), 7.03 (t, J = 7.3 Hz, 2H), 3.49 (s, 1 H), 2.76 (m, 5H), 2.15 (m, 2H), 1.77 (m, 3H).

¹³ CNMR (100 MHz, DMSO-D6) 5 161.5, 171.6, 168.5, 166.9, 159.1 , 148.2, 145.3, 140.7, 136.3, 131.9, 130.3, 128.1 , 127.6, 124.0, 121.0, 118.5, 67.7, 60.9, 58.0, 48.9, 34.1 , 29.5, 23.6.

MP: 87-89 °C.

Molecular Formula = C22H20N4O5

Formula Weight = 420.41

19) 1'-((5-(2,5-dimethoxyphenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-one: [Xaj]

IR: 2926.0, 2832.8, 1681.0, 1602.8, 1543.1 , 1461.1 , 1326.9, 1222.6, 1017.6, 805.1 , 738.0cm- ¹ .

¹ HNMR (400 MHz, CDCI3) 5 7.88 (dd, J = 8.0, 1.4 Hz, 1 H), 7.60 (d, J = 3.1 Hz, 1 H), 7.54 - 7.50 (m, 1 H), 7.02 (d, J = 7.8 Hz, 2H), 6.95 (dd, J = 9.0, 3.2 Hz, 1 H), 6.86 (d, J= 9.0 Hz, 1H), 3.85 (s, 3H), 3.82 (s, 3H), 3.49 (s, 2H), 2.81 -2.69 (m, 6H), 2.14 (d, J= 12.1 Hz, 2H), 1.90-1.75 (m, 2H).

¹³ CNMR (100 MHz, DMSO-D6) 5191.6, 171.1, 168.8, 159.1, 153.4, 152.4, 143.8, 140.7, 137.3, 136.0, 132.0, 130.3, 126.2, 123.3, 121.0, 120.6, 118.4, 112.6, 110.2, 60.9, 58.0, 55.7, 48.9, 34.0, 29.5.

MP: 102-104 °C

Molecular Formula = C24H25N3O5

Formula Weight = 435.47

20) 1'-((5-(3,4-dimethoxyphenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-one:[ Xak]

IR: 2922.2, 2855.1, 1684.8, 1602.8, 1513.3, 1461.1, 1338.1, 1300.8, 1263.6, 1230.0, 1114.5, 715.4, 690.3cm- ¹ .

¹ HNMR (400 MHz, DMSO-D6) 57.86 (dd, J= 7.9, 1.6 Hz, 1H), 7.54-7.43 (m, 2H), 7.11 (dd, J= 8.2, 1.8 Hz, 1H), 7.01 (t, J= 8.0 Hz, 2H), 6.85 (d, J = 8.3 Hz, 1H), 3.93 (s, 3H), 3.90 (s, 3H), 3.47 (s, 2H), 2.86 - 2.67 (m, 6H), 2.17-2.10 (m, 2H), 1.81 (dt, J= 15.1, 5.8 Hz, 2H).

¹³ CNMR (100 MHz, DMSO-D6) 5191.6, 166.1, 159.1, 151.0, 150.6, 149.2 148.4, 143.6, 140.8, 136.3, 132.1, 133.5, 128.0, 127.3, 126.2, 122.5, 121.4, 120.7, 118.5, 111.2, 108.4, 60.9, 57.9, 56.1, 48.9, 47.7, 33.9, 29.5.

MP: semi solid

Molecular Formula = C24H27N3O5

Formula Weight = 437.48

21)1'-((5-(3,4,5-trimethoxyphenyl)-1,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-one: [Xal]

IR:2914.3, 2855.1 , 1669.8, 1650.8, 1591.6, 1453.7, 1408.9, 1282.2, 1252.4, 1121.9, 1036.2, 793.9, 738.0cm- ¹ .

¹ H NMR (400 MHz, CDCh) 5 7.84 - 7.69 (m, 2H), 7.51 - 7.38 (m, 2H), 7.21 - 7.06 (m, 2H), 3.84 (m, 6H), 3.76 (s, 3H), 3.51 (s, 2H), 3.13 (s, 2H), 2.76 (d, J = 11 .4 Hz, 2H), 2.60 (dd, J = 11 .4, 8.8 Hz, 2H), 1 .99 (d, J = 12.6 Hz, 2H), 1.90 - 1.79 (m, 2H).

¹³ CNMR (100 MHz, DMSO-D6) 5 191.7, 166.5, 159.0, 153.3, 148.4, 139.6, 136.3, 131.1 , 129.5, 128.5, 126.2, 120.9, 118.4, 116.8, 105.5, 104.0, 73.0, 67.8, 60.8, 56.1 , 48.9, 34.0, 29.5, 22.5, 14.1.

MP: Semi solid

Molecular Formula = C25H27N3O6

Formula Weight = 465.49

22) 1'-((5-(benzo[d][1,3]dioxol-5-yl)-1,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-one: [Xam]

IR: 3082.5, 2918.5, 1688.5, 1602.8, 1561.8, 1438.8, 1259.8, 1036.2,

741.7, 693.3cm- ¹ .

¹ HNMR (400 MHz, DMSO-D6) 5 7.54 (t, J = 8.6 Hz, 1 H), 7.40 - 7.28 (m, 1 H), 7.21 (m, 1 H), 7.12 - 6.98 (m, 3H), 6.97 - 6.88 (m, 1 H), 6.04 (s, 2H), 3.56 (s, 2H), 2.78 (s, 2H), 2.68 - 2.49 (m, 3H), 2.36 (m, 1 H), 2.02 - 1.69 (m, 4H).

¹³ CNMR (100 MHz, DMSO-D6) 5 174.3, 172.0, 169.2, 167.6, 160.8, 148.2, 144.3, 136.3, 131.4, 130.4, 128.7, 126.3, 120.6, 118.7, 116.0, 108.2, 105.6,

101.7, 49.0, 38.5, 33.9, 30.2, 28.8, 41.1. MP: 115-117 °C

Molecular Formula = C23H2iBrN30s

Formula Weight = 419.42

23) 7-bromo-1'-((5-(2-chlorophenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-one: [Xba]

IR:2922.2, 2840.2, 1684.8, 1591.6, 1416.4, 1282.2, 1218.8, 1125.7,

909.5, 801.4, 760.4cm- ¹ .

¹ HNMR (400 MHz, CDCI3) 5 7.71 (d, J = 8.3 Hz, 1 H), 7.37 (dd, J = 7.9, 1.4 Hz, 1 H), 7.34 - 7.28 (m, 2H), 7.23 (d, J = 1.8 Hz, 1 H), 7.15 (dd, J = 8.4, 1.8 Hz, 1 H), 3.48 (s, 2H), 2.74-2.69 (m, 6H), 2.11 (d, J = 12.2 Hz, 2H), 1.87 - 1.78 (m, 2H).

¹³ CNMR (100 MHz, DMSO-D6) 5 190.8, 171.3, 166.8, 159.4, 144.3, 140.0,

133.9, 131.5, 130.3. 129.7, 127.5, 126.8, 124.5, 121.4, 119.7, 60.9, 58.0,

48.9, 33.9, 29.5, 22.8, 14.3.

MP: semi solid

Molecular Formula = C22Hi9BrCIN3C>3

Formula Weight = 488.76

24) 7-bromo-1'-((5-(4-chlorophenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-one: [Xbb]

IR:2912.8, 2817.9, 1669.8, 1591.6, 1535.7, 1416.4, 1218.3, 1084.7, 801.4, 738.0, 689.5cm- ¹ . ¹ HNMR (400 MHz, DMSO-D6) 6 7.81 (d, J = 8.1 Hz, 1 H), 7.70 - 7.58 (m, 4H), 7.46 (dd, J = 8.5, 6.6 Hz, 2H), 3.54 (s, 2H), 2.80 (s, 2H), 2.60-2.49 (m, 4H), 1.87 (t, J = 17.5 Hz, 2H), 1.81 - 1.79-1.71 (m, 2H).

¹³ CNMR (100 MHz, DMSO-D6) 5 190.6, 166.2, 161.1 , 159.4, 159.1 , 147.3,

136.3, 131.9, 130.9, 129.7, 129.2, 129.0, 128.8, 128.2, 127.8, 124.9, 121.5, 119.5, 61.1 , 49.2, 49.0, 47.7, 34.3.

MP: 106-108 °C

Molecular Formula = CggHigBrCINsOs

Formula Weight = 488.78

25) 7-bromo-1'-((5-(4-bromophenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-one: [Xbc]

IR: 2920.2, 2825.3, 1688.5, 1595.3, 1561.8, 1422.1 , 1941.8, 1285.9, 1218.8, 820.0, 741.7, 93.3cm- ¹ .

¹ HNMR (400 MHz, DMSO-D6) 5 7.81 (d, J = 7.8 Hz, 1 H), 7.60 (td, J = 8.3, 4.5 Hz, 4H), 7.33 - 7.28 (m, 1 H), 7.20 (dd, J = 8.4, 1.7 Hz, 1 H), 3.67 (s, 2H), 2.81 (d, J = 6.4 Hz, 2H), 2.71 - 2.57 (m, 2H), 2.55 - 2.48 (m, 2H), 1 .96 - 1.67 (m, 4H).

¹³ CNMR (100 MHz, DMSO-D6) 5 190.7, 171.3, 168.3, 166.4, 159.4, 147.0,

142.4, 140.9, 134.3, 133.4, 132.3, 131.5, 130.3 128.4, 126.2, 124.5, 123.5,

120.5, 119.6, 60.8, 57.9, 48.9, 47.5, 33.9.

MP: 120-122 °C

Molecular Formula = CggHigBrgNsOs

Formula Weight = 533.21

26) 7-bromo-1'-((5-(4-nitrophenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-one: [Xbd]

IR: 292.0, 2855.1 , 1688.5, 1591.6, 1561.8, 1338.1 , 1282.2, 1121.9, 738.0, 693.3cm' ¹ .

¹ H NMR (400 MHz, CDCh) 5 8.26 (d, J = 8.8 Hz, 2H), 7.91 (d, J = 8.8 Hz, 2H), 7.53 (dd, J = 5.7, 3.3 Hz, 1 H), 7.25 - 7.06 (m, 2H), 3.58 (s, 2H), 2.87 - 2.60 (m, 5H), 2.24 - 1.82 (m, 5H).

¹³ CNMR (100 MHz, DMSO-D6) 5 190.7, 171.6, 168.5, 159.5, 148.2, 145.3, 140.7, 134.3, 131.4, 130.2, 128.7, 127.7, 124.4, 121.4, 119.7, 60.9, 58.0, 48.8, 47.5, 34.0, 28.8, 23.6.

MP: 106-108 °C

Molecular Formula = C22Hi9BrN40s

Formula Weight = 499.31

27) 7-bromo-1'-((5-(4-methoxyphenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-one [Xbf]

IR:3082.5, 2996.3, 2948.3, 1669.8, 1591.6, 1416.4, 1244.9, 1025.0, 980.3, 913.2, 861.0cm' ¹ .

¹ H NMR (400 MHz, DMSO-D6) 5 7.85 (d, J = 8.1 Hz, 2H), 7.71 (td, J = 7.4, 0.9 Hz, 2H), 7.35 (d, J = 1.8 Hz, 1 H), 7.10 - 6.92 (m, 2H), 3.80 (d, J = 2.2 Hz, 3H), 3.61 (s, 2H), 2.91 - 2.59 (m, 6H), 2.06 - 1.65 (m, 4H).

¹³ CNMR (100 MHz, DMSO-D6) 5 190.7, 170.5, 168.5, 166.0, 161.5, 159.5, 147.9, 143.5, 137.3, 132.2, 130.5, 129.0, 128.1 , 127.0, 124.5, 121.4, 119.8, 114.2, 67.7, 60.8, 57.8, 55.5, 48.9, 47.4, 38.5, 33.7.

MP: semi solid

Molecular Formula = C23H22BrNsO4

Formula Weight = 484.34 28) 7-bromo-1'-((5-(2,5-dimethoxyphenyl)-1 ,3,4-oxadiazol-2- l)methyl)spiro[chromane-2,4'-piperidin]-4-one:[ Xbj]

IR: 2996.8, 2896.1 , 2832.8, 1684.8, 1591.8, 1420.1 , 1222.8, 1047.4, 797.7, 708.2cm- ¹ .

¹ HNMR (400 MHz, CDCh) 5 7.71 (dd, J = 8.4, 5.0 Hz, 1 H), 7.58 (d, J = 3.1 Hz, 1 H), 7.23 (d, J = 1.7 Hz, 1 H), 7.15 (dd, J = 8.4, 1.8 Hz, 1 H), 6.94 (dd, J = 9.0, 3.2 Hz, 1 H), 6.84 (dd, J = 9.0, 2.2 Hz, 1 H), 3.84 (s, 3H), 3.80 (s, 3H), 3.48 (s, 2H), 2.79 - 2.55 (m, 6H), 2.09 (t, J = 12.3 Hz, 2H), 1.87 - 1.75 (m, 2H).

¹³ CNMR (100 MHz, DMSO-D6) 5 190.7, 171.3, 166.3, 159.5, 153.4, 152.4, 143.9, 139.4, 134.3, 131.6, 130.3, 127.7, 126.2, 124.4, 122.6, 120.5, 118.2, 112.6, 110.1 , 60.9, 58.1 , 55.7, 48.7, 34.0.

MP: 116-118 °C.

Molecular Formula = C24H24BrN30s

Formula Weight = 514.36

29) 7-bromo-1'-((5-(3,4-dimethoxyphenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-one:[ Xbk]

IR:3082.5, 2983.4, 2834.5, 1688.5, 1593.8, 1561.8, 1513.3, 1341.8, 1267.3, 1233.7, 1021.3, 741.7, 693.3cm- ¹ .

¹ HNMR (400 MHz, DMSO-D6) 5 7.81 (d, J = 8.1 Hz, 2H), 7.72 - 7.58 (m, 3H), 7.12 (d, J = 8.1 Hz, 1 H), 6.98 (d, J = 8.3 Hz, 1 H), 3.76 (s, 6H), 3.51 (s, 2H), 2.82 (d, J = 16.9 Hz, 2H), 2.55 (m, 4H), 1.84 (m, 4H). ¹³ CNMR (100 MHz, DMSO-D6) 6 190.6, 187.8, 177.3, 159.2, 150.9, 149.1 , 134.3, 131.6, 130.3, 127.7, 126.1 , 125.4, 124.6, 122.7, 121.4, 120.2, 119.6, 110.7, 108.4, 60.4, 57.8, 48.7, 33.8.

MP: 117-119 °C

Molecular Formula = C24H24BrN30s

Formula Weight = 514.36

30) 7-bromo-T-((5-(3,4,5-trimethoxyphenyl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro-[chro-mane-2,4'-piperidin]-4-one: [Xbl]

IR: 3082.5, 2933.4, 1688.5, 1591.6, 1561.8, 1416.4, 1338.1 , 1125.7, 998.0, 741.7cm- ¹ .

¹ HNMR (400 MHz, DMSO-D6) 5 7.64 - 7.60 (m, 1 H), 7.38 - 7.15 (m, 2H), 7.03 - 6.91 (m, 2H), 3.79 (2s, 6H), 3.66 (s, 3H), 3.55 (s, 2H), 2.98 - 2.78 (m, 2H), 2.76 - 2.50 (m, 2H), 2.43 - 2.27 (m, 2H), 2.08 - 1 .64 (m, 4H).

¹³ CNMR (100 MHz, DMSO-D6) 5 168.5, 164.6, 159.7, 153.3, 134.3, 131.5, 131.4, 130.3, 126.3, 120.7, 60.5, 56.1 , 48.8.

MP: 132-134 °C.

Molecular Formula = C25H26BrN30e

Formula Weight = 544.39

31) 1'-((5-(benzo[d][1 ,3]dioxol-5-yl)-1 ,3,4-oxadiazol-2-yl)methyl)-7- bromospiro-[chromane-2,4'-piperidin]-4-one: [Xbm]

IR: 2922.2, 2855.1 , 1669.8, 1591.6, 1453.7, 1408.9, 1282.2, 1252.4, 1121.9, 1036.2, 805.2, 738.0cm- ¹ . ¹ HNMR (400 MHz, CDCI3) 6 7.72 (dd, J = 8.4, 2.8 Hz, 1 H), 7.41 (d, J = 1.5 Hz, 1 H), 7.23 (d, J = 1.7 Hz, 1 H), 7.16 (dd, J = 8.3, 1.7 Hz, 1 H), 7.08 (dd, J = 8.0, 1.5 Hz, 1 H), 6.81 (d, J = 7.9 Hz, 1 H), 6.01 (s, 2H), 3.49 (s, 2H), 2.79 - 2.66 (m, 6H), 2.09 (dd, J = 12.3, 10.3 Hz, 2H), 1.95-1.85 (m, 2H).

¹³ CNMR (100 MHz, DMSO, -D6) 5 190.8, 170.9, 166.1 , 159.5, 148.3, 147.7, 143.1 ,140.7, 134.4, 132.0, 131.8, 130.4, 128.9, 127.9, 126.5, 124.5, 123.7, 121.4, 119.9, 108.4, 105.5, 94.1 , 60.8, 57.8, 48.8, 47.3, 33.9, 29.5.

MP: 88-90 °C.

Molecular Formula = C23H2oBrN30

Formula Weight = 498.32

32) 7-bromo-1'-((5-(naphthalen-2-yl)-1 ,3,4-oxadiazol-2- yl)methyl)spiro[chromane-2,4'-piperidin]-4-one: [Xbn]

IR: 2922.4, 2855.1 , 2817.9, 1673.6, 1595.3, 1416.4, 1244.9, 1196.5, 1166.7, 1025.0, 857.3, 801.2, 734.3, 685.8cm- ¹ .

¹ HNMR (400 MHz, CDCI3) 5 8.33 (s, 1 H), 8.01 - 7.94 (m, 2H), 7.73 (dd, J =

15.8, 8.5 Hz, 3H), 7.23 (d, J = 1.7 Hz, 1 H), 7.14 (td, J = 6.6, 3.3 Hz, 3H), 3.78 (s, 2H), 2.78 - 2.67 (m, 6H), 2.11 (d, J = 12.2 Hz, 2H), 1.84 - 1.75 (m, 2H).

¹³ CNMR (100 MHz, DMSO-D6) 5 190.8, 171.2, 166.3, 159.5, 158.6, 148.6,

143.8, 135.6, 130.2, 129.8, 128.4, 127.6, 124.5, 123.9, 121.4, 119.8, 119.3, 106.2, 60.9, 58.7, 55.4, 48.9, 47.5, 34.0, 29.5.

MP: 122-124 °C.

Molecular Formula = C26H22BrN30s

Formula Weight = 504.37 Anti-tubercular activity

In the quest of synthesising newer anti tubercular compounds, 35 new spiro[chromane-2,4'-piperidine]-4(3/7)-onefunctionalized compounds have been synthesized to understand the effect of substitution of various groups on chromane scaffold in order to get anti tubercular activity. These compounds were studied for their anti-Mycobacterium tuberculosis H37 Rv ATCC 25177 (sensitive to all anti-mycobacterial, anti-biotics)activity with the use of BD Bactec MGIT 320, an automated system for Mycobacteria testing through non-invasive, non-radiometric fluorescence technology method. The results of in vitro anti-tubercular activitycompared with pyrazinamide are presented in Table 1 (at 100pg/ ml) for all compounds. In addition, those compounds showed promising activity at 100pg/ ml werealso tested at lower concentration (12.5, 25, 50 and 75pl) and their resultsare summarized in Table 2.

In vitro anti-tubercular activity evaluation

The anti-mycobacterial activities of the synthesized compounds were performed at three level safety laboratories at Tech Trans Laboratory Pune, India and anti-tubercular activities at K.E.M. Hospital, Pune, India. The anti- tubercular activity of the test compounds was determined by using BD Bactec MGIT 320, a fully automatic system. 7 ml of Modified Middlebrook 7H9 broth is used in each Mycobacteria Growth Indicator Tube (MGIT), with a non-radiometric fluorescence technology, continuous monitoring system.Alamar blue dye (Accumed International, Westlake Ohio), microtiter plates (Falcon, 3072: Becton Dickinson, Lincoln Park NJ), sterilized glass wares, UV-cabinets with reversepressure gas system. The preserved strains of M. tuberculosis, sensitive to pyrazinamide (PZA)- H37Rv (ATCC 25177) was used inorder to assess the anti-mycobacterial activity of the synthesized spiro-cyclicderivatives. Preparation of the drugs/compounds dilutions

Individual stock solutions of 700 pg/100plDMSO concentration of all the test compounds were prepared by dissolving the requisite quantity of compounds in Dimethyl Sulfoxide.100 plof this stock solution was then added in 7 ml culture medium, in MGIT to get 100pg/ ml concentration of the test compounds containing Mycobacterium tuberculosis cultures H37 Rv ATCC 25177.

In the same way, different concentration of the test compounds were prepared by adding 12.5, 25, 50 and 75pl stock solution of individual compounds to 7 ml culture medium in the MGIT to get 12.5, 25, 50 and 75pg I ml concentration of the test compounds. Similarly, stock solution of50 mg/ml concentration was prepared for standard anti-tuberculardrug, pyrazinamide and diluted to 25 mg/ml in order to check the anti-tubercular activity.

Preparation of growth media

It was prepared by adding dehydrated medium (19 g) to purifiedwater (900 ml) containing glycerol (15 ml). The mixture wasstirred well to dissolve and autoclaved at 121°Cfor 10 min. Oleicacid-albumin catalase (100 ml) was aseptically added to the medium after cooling to 45°C. No adjustment for pH was made.

Positive control.

Positive control for the anti-tubercular activity test was prepared by adding Pyrazinamide (source of the antibiotic- which manufacturer, batch number Date of manufacturing and expiry) stock solution in DMSO to MGIT, each containing7 ml culture. Appropriate amount of this stock solution (700pg Pyrazinamide Z1 OOpI DMSO) was added to culture media to get 12.5, 25, 50, 75 and 100pg/ ml concentration in the culture media. Negative controls.

Two negative controls were prepared. Solvent blank was prepared by adding requisite amount of DMSO (solvent) to the culture medium. Similarly, culture control was prepared by adding bacterium culture to the medium.

Experimental details for random screening of the isolated compounds for anti-tubercularactivity

The anti-mycobacterial activity of compounds was assessed against mycobacterium sensitive to PZA-H37Rv(ATCC 25177) using the microplate turbidity assay. This methodology is nontoxic, uses a thermally-stable reagent and is suitable for random screening of the anti mycobacterial activity. Briefly, 200 pL of sterile deionised water was added to all outerperimeter wells of sterile 96 well plates to minimizeevaporation of the medium in the test wells during incubation. The 96 well plates received 100 pL of the Middlebrook 7H9 broth(having loopful inoculum of bacteria-108 CFU) and different dilutions of the respective compounds were made directly on the plate. The maximum concentration of the compounds tested was 50 mg/ml. The MGIT containing test compounds, positive and negative controls were incubated at 37°C for 41 days. Observations were recorded on daily basis to record turbidity in the culture, indicating growth of the bacterium in the medium, thus showing end of static activity of the compounds at that concentration.

Table 1 :/n vitro percent inhibition of enzymes in Mycobacterium tuberculosis H37Rv at 100 pg/ ml concentration

No growth- There was no growth seen till end of experiment that is till 41 ^st day.

Table (1) (A)

Table 2: Anti TB test with selected compounds at lower concentrations

Advantages of the invention.

1. The inventions provides Tricyclic spiro[chromane-2,4'-piperidin]- 4(3H)-one with 1 ,3,4-oxadiazole linkers compositions and process for preparation thereof as potent precursors of anti-tubercular agents.

2. The invention provides for compounds with inclusion of oxadiazole into the backbone of spiropiperidinyl chromanone unit to make sure that the new moiety has potent anti-tubercular properties based on a whole cell screen, under multiple physiological conditions on replicating Mtb.