Antimicrobial and larvicidal activities of 2-hydroxypyrrolidine / piperidine derivatives

A novel series of various 2-hydroxypyrrolidine/piperidine derivatives were synthesized and their antibacterial activity against MTCC bacterial strains, anticancer activity and larvicidal effects were studied. Among the ten synthesized compounds, three were found to be antibacterial in nature. All the five test strains were highly sensitive to 1-(quinolin-3-yl) pyrrolidin-2-ol (P7), moderately sensitive to 1-(pyridin-4-yl) pyrrolidin-2-ol (P3) and less significantly to 1-(pyyrolidin-2-yl) piperidin-2-ol (p8). The maximum zone of inhibition was 28 ± 0.14 mm against Escherichia coli (MTCC 78) followed by 23± 0.14 mm against Klebsiella pneumoniae with 100 percent of relative inhibitory zone. The relative inhibitory zone of P3 against E.coli was 56% and 80 % against Klebsiella pneumoniae. Similarly 1-(quinolin-3-yl) pyrrolidin-2-ol (P7) showed a 60 % of larvicidal activity against Anaphelous sp and 53% against Culex sp.


Introduction
Heterocyclic compounds especially pyrrolidine and piperidines are considered as pharmaceutically important biologically active compounds have been used as Vitamins, hormones and antibiotics [1][2][3].Pyrrolidine and piperidine occupied a unique place in the development of pharmacologically active substance by replacing the nucleus [4,5].Piperidine nucleus is an important core of many drug molecules.Piperidine and its analogues are reported in literature for varied pharmacological activities like antihistamines, anticancer, and antibacterial [6].The tetrahydropyrrolidine moiety is present in various natural products and they exhibit a broad range of biological activities.Codonopsinine and Codonopsine are the derivatives of pyrrolidine, isolated from Codonopsis chematidea, which have been found to possess hypotensive pharmacological activity [7].Lilidine, an alkaloid occurring in the epigeal parts of Lilium Martagon which contains pyrrolidine analog has been isolated and reported [8].N-alkylated-D-fagomine derivatives and N-alkylated hydroxylated pyrrolidine bearing an improved inhibitory selectivity towards α-D-glucosidase and α-L-fucosidase, respectively.Cell lines compared to their nonalkylated progenitors.Barbara et al., have been reported a series of 1-substituted pyrrolidin-2-one and pyrrolidine derivatives were synthesized and tested for electrocardiographic, antiarrhythmic and antihypertensive activity as well as adrenoceptors binding affinities [8][9][10].Biologically active alkaloids of substituted piperidines ring system have been targeted for their total or partial synthesis.Piperidine was first isolated from the alkaloid piperine, which occurs in black pepper.Piperidine fragment was substituted via variety of synthetic reactions to develop more improved moieties with enhanced activities and to suppress the side effects when taken as medicine for different ailments.Specifically, piperidine based chemical entities with aryl substituent's have been documented as potent microbial agents [9].Developing antimicrobial drugs and maintaining their potency, in opposition to resistance by different group of microorganisms as well as a broad spectrum of antimicrobial activity major concern of research in this area.Mosquito's are one of the major vectors responsible for the transmittance of diseases to more than 700 million people annually.Control of such diseases is becoming increasingly difficult because of increasing resistance of mosquitoes to pesticides [11].

Experimental Studies
All anhydrous solvents and reagents were obtained from commercial suppliers and used without any further purification unless otherwise noted [Merck and Alfa Aesar products].All the reactions were carried out in the closed condition.The melting points of the synthesized compounds were measured on EZ -Melt automated melting point apparatus.IR spectra were recorded on Shimadzu FT-IR spectrometer using KBr pellet in the 400-4000 cm -1 region.The IR spectra were recorded from St. Joseph College, Trichy.The NMR spectral studies were carried out using Bruker 300 MHz spectrometer using TMS as an internal standard and DMSO-d 6 as solvent and recorded at Sastra University, Tanjore.Mass spectra were recorded on a JEOL GCMATE II GC-MS spectrometer using a direct injection method.The mass spectra were recorded from IIT Madras, Chennai.

General Synthesis of 2-hydroxypyrrolidine/piperidine derivatives
Among the different approaches employed for the synthesis of 2-hydroxypyrrolidine and piperidine derivatives, one pot synthesis method is the most efficient.To the mixture of 2,3-cyclic ethers and acetonitrile, heterocyclic amine was added and followed by CeCl 3 .7H 2 O.The reaction condition was maintained at 60 °C using silicone oil bath and the contents were kept over a magnetic stirrer and stirred well.The colorless was solid separated and washed several times with water [12][13][14].

Antimicrobial effect of 2-hydroxy Pyrrolidine/ Piperdine derivatives (11=15)
The antibiotic sensitivity of the isolates was determined using the disc diffusion method.Standardized inoculum of the 0.5 Mcfarnald overnight grown Nutrient agar culture of E. coli (MTCC 78), P. aeruginosa (MTCC 2488), S. aureus (MTCC 96), B. subtilis (MTCC 121), K. pneumoniae (MTCC 109) were spread on Mueller-Hinton agar plates using sterile swabs.The plates were dried at room temperature for 20 min and 100 µl (5 mg /ml) of synthesized pyrrolidine and piperidine derivatives loaded on their respective wells and allowed to diffuse.The plates were incubated for 24 h at 37°C.All the tests were triplicate and the diameter of zone of inhibition was measured and statistically reported [15].

Screening of larvidial effect of 2-hydroxy Pyrrolidine/ Piperdine derivatives
About 100 ml of sterile tap water was taken in conical flask and one ml of pyrrolidine and piperidine derivatives were added to obtain 10 ppm concentration.The control tubes were maintained as tap water alone.25 numbers of 3 rd instar Anopheleses and Culex mosquito larvae were inoculated into the above tubes and incubated at 2°C for 48 h.The larvicidal activity was observed for over 30 min.and death of the larvae confirmed the larvicidal activity.The experiment was checked daily for recording the biological effects of following criterias [19].
Larval mortality percent: was estimated by using the following equation:

Larval mortality % = A -B / A × 100
Where A = number of tested larvae and B = number of tested pupa

Papal mortality % = A -B / A × 100
Where A = number of produced pupae and B = number of observed adults.

Adult emergence % = A / B × 100
Where A = number of emerged adults and B =number of tested pupae.

Synthesis of 1-(quinolin-3-yl)pyrrolidin-2-ol (P7):
To a solution of 3-aminoquinoline (1.18 mmol) in acetonitrile (5 mL), 2,3-dihydrofuran (1.4 mmol) was added followed by cerium chloride hexa hydrate (CeCl 3 .6H 2 O) (0.59 mmol) at 0°C.The reaction mixture was kept in an oil bath maintained at 60° C and stirred well for 30 min.Progress of the reaction was continuously monitored by LCMS.The reaction mixture was diluted with ethyl acetate and washed with water.The organic layer was dried over Na 2 SO 4 and concentrated by vacuum.The crude mass obtained was purified by column Chromatography packed with 60/120 silica gel and eluted with 25-35% ethyl acetate in petroleum ether.The above procedure was employed for the preparation of remaining compounds.

Conclusion
Result of present study demonstrates that, a new class of 2-hydroxypyrrolidine & 2-hydroxypiperidine derivatives were synthesized and evaluated as antibacterial agents.The newly synthesized heterocyclics 1-(quinolin-3-yl) pyrrolidin-2-ol (P7)) exhibited promising antibacterial, anticancer activity and larvicidal activity at minimal concentration level.It can be concluded that this class of compounds certainly holds great promise towards medicinal chemistry.A further study to acquire more information concerning pharmacological activity is in progress.To exploit these findings for human welfare, it is necessary to carry out field trials and in vivo studies to explore as valuable bioactive substance.