Patent Publication Number: US-2021179605-A1

Title: Discovery of Novel First in Class Nature-Inspired Compounds Targeting the Mitochondrial Function and Pharmaceutical Composition Thereof

Description:
FIELD OF THE INVENTION 
     The present invention relates to novel antitumor agents and pharmaceutically acceptable salts thereof, processes and intermediates for the manufacture of these novel constrained cyclic frameworks as defined in the specification of general formula I and II, and medicaments containing such compounds. This invention also concerns the use of such compounds to modulate the cellular mitochondrial functions by measuring the ATP content, the mitochondrial membrane potential and the cellular redox potential as well as their toxicities and effects on T and B cells. 
     
       
         
         
             
             
         
       
     
     BACKGROUND OF THE INVENTION (PRIOR ART) 
     Natural product estate represents a wealth of structural diversity with high 3D-content; however, there are well-documented difficulties linked to their use in screening experiments including their availability for clinical trials and SAR development (A. Isidro-Llobet et al., Diversity-oriented synthesis of macrocyclic peptidomimetics,  Proc. Natl. Acad. Sci., USA,  2011, 108, 6793; T. Gaich et al., Aiming for the Ideal Synthesis,  J. Org. Chem.,  2010, 75, 4657). Thus the recent decade or so has witnessed an upsurge in the development of privileged substructure diversity-oriented synthesis strategies for the de novo construction of nature-inspired compounds needed for phenotypic screening campaigns (N. J. Green et al., Bio-inspired Domino oxa-Michael/Diels-Alder/oxa-Michael Dimerization of para-Quinols,  Angew. Chem. Int. Ed,  2018, 57, 6198; K. Mukai et al., Bioinspired chemical synthesis of monomeric and dimeric stephacidin A congeners,  Nat. Chem.,  2018, 10, 38). One such strategy represents the use of a single pluripotent functional group that can be decorated through reactions with a variety of reagents, thereby empowering the synthesis of skeletally diverse compound collections with high 3D-content (J. Cui et al., Creation and manipulation of common functional groups en route to a skeletally diverse chemical library,  Proc. Natl. Acad. Sci, USA.  2011, 108, 6763). Currently, there is growing consensus that, increasing the 3D-content and the number of stereocenters within specific library has been suggested to enhance the selectivity and potency toward a given target, hence increases the hit to lead success rate across several targets from a single library (F. Nie, A Multidimensional Diversity-Oriented Synthesis Strategy for Structurally Diverse and Complex Macrocycles,  Angew. Chem. Int. Ed. Engl.,  2016, 55, 11139). 
     To this end, one of the important classes of natural products with high 3D-content, is the octahydroindolo[2,3-a]quinolizine monoterpene indole alkaloids, comprised of more than 2000 members and among the most studied natural product classes owing to their diverse biological activities and synthetic potential associated with these scaffolds (S. E. O&#39;Connor et al., Chemistry and biology of monoterpene indole alkaloid biosynthesis.  Nat. Prod. Rep.,  2006, 23, 532; A. E. Laine et al., Pharmacological importance of optically active tetrahydro-β-carbolines and synthetic approaches to create the C1 stereocenter,  Molecules,  2014, 19, 1544). This molecular framework is produced by an array of plants and microorganisms. Several members of this monoterpene family possess biological activities useful for the treatment of many disease states (S. E. O&#39;Connor et al., Chemistry and biology of monoterpene indole alkaloid biosynthesis.  Nat. Prod. Rep.,  2006, 23, 532; M. G. Sankar et al., Stereoselective synthesis of a natural product inspired tetrahydroindolo[2,3-a]-quinolizine compound library.  Bioorg. Med Chem.  2015, 23, 2614). Despite the existence of various multi-step stereoselective methods, direct access to diverse variants of these systems in a completely diastereo-controlled, step-economic, and atom-economic manner would be a remarkable achievement. In this context, Sarpong and Stork reported innovative approaches for the synthesis of various scaffolds of this class of natural products (T. P. Lebold et al., A divergent approach to the synthesis of the yohimbinoid alkaloids venenatine and alstovenine,  Nat. Chem.,  2013, 5, 126; G. Stork et al., Regiospecific and Stereoselective Syntheses of (±)-Reserpine and (−)-Reserpine,  J. Am. Chem. Soc.,  2005, 127, 16255). Furthermore, Shu-Li You (S. G. Wang et al., Construction of Chiral Tetrahydro-β-Carbolines: Asymmetric Pictet-Spengler Reaction of Indolyl Dihydropyridines,  Angew. Chem. Int. Ed.,  2017, 56, 7440) and Hongbin Zhai (S. Luo et al., A Fast Assembly of Pentacyclic Benz[f]indolo[2,3-a]quinolizidine Core by Tandem Intermolecular Formal Aza-[3+3] Cycloaddition/Pictet-Spengler Cyclization: A Formal Synthesis of (±)-Tangutorine,  J. Org. Chem.,  2004, 69, 4548) described elegant synthesis of these scaffolds employing variants of Pictet-Spengler reaction. Additionally, important contributions to access this class of natural products were also reported by Yasumasa Hamada (T. Nemoto et al., Catalytic Asymmetric Total Synthesis of Tangutorine,  Org. Lett.,  2010, 12, 872), Erwan Poupon, (R. Salame et al., Biomimetic Synthesis of Tangutorine Following New Biogenetic Proposals,  Org. Lett.,  2009, 11, 1891) and Mercedes Amat, (F. Arioli et al., Stereoselective Total Synthesis of the Putative Structure of Nitraraine,  J. Org. Chem.,  2014, 79, 7740). Despite the importance of these stepwise stereoselective methods, a general and modular strategy for the preparation of various analogues of the octahydroindolo[2,3-a]quinolizine monoterpene indole alkaloids family is highly desirable. 
     In addition, spiro-oxindole scaffolds represent the basic framework of a wide range of natural products and biologically significant compounds, including anitiviral (N. Ye et al., Therapeutic Potential of Spirooxindoles as Antiviral Agents.  ACS Infect. Dis.  2016, 2, 382), anticancer (B. Yu et al., Spirooxindoles: Promising scaffolds for anticancer agents.  Eur. J. Med. Chem.  2015, 97, 673) activities as well as cell cycle inhibitors (C. B. Cui et al., Novel mammalian cell cycle inhibitors, spirotryprostatins A and B, produced by  Aspergillus fumigatus , which inhibit mammalian cell cycle at G2/M phase.  Tetrahedron,  1996, 52, 12651). For example, a natural product spirotryptostatin, showed a promising anticancer activity (L. Chen et al., Design, Synthesis, and Biological Activities of Spirooxindoles Containing Acylhydrazone Fragment Derivatives Based on the Biosynthesis of Alkaloids Derived from Tryptophan.  J. Agric. Food Chem.  2016, 64, 6508). 
     On the other hand, targeting the mitochondrial function has been implemented as a potential anticancer approach by depriving cancer cells from a main energy source (S. E. Weinberg et al., Targeting mitochondria metabolism for cancer therapy,  Nat. Chem. Biol.,  2015, 11, 9; P. E. Porporato, et al., Mitochondrial metabolism and cancer,  Cell Res.,  2018, 28, 265) Limiting the mitochondrial energy production affects the availability of ATP in cancer cells and so the biosynthesis of macromolecules and the cell signaling required for tumor growth (P. S. Ward et al., Metabolic reprogramming: a cancer hallmark even warburg did not anticipate, Cancer cell, 2012, 21, 297; S. Y. Lunt et al., Aerobic glycolysis: meeting the metabolic requirements of cell proliferation,  Annu. Rev. Cell. Dev. Biol.,  2011, 27, 441). While several approaches to identify modulators of mitochondrial functions have been developed they mostly rely on screening of widely known chemical structures and agents (P. A. Andreux, et al., A method to identify and validate mitochondrial modulators using mammalian cells and the worm  C. elegans. Sci. Rep.,  2014, 4, 5285; B. K. Wagner et al., Large-scale chemical dissection of mitochondrial function,  Nat. Biotechnol.,  2008, 26, 343; K. B. Wallace et al., Mitochondrial off targets of drug therapy,  Trends Pharmacol Sci.,  2008, 29, 361). The approach presented here aims to evaluate and develop novel chemical structures with enhanced effects on mitochondrial and cellular functions to modulate the cellular metabolism to tackle cancer cells proliferation and survival. The present invention introduces a one-pot practical and modular approaches to access diversely functionalized novel heterocyclic systems with more than three contiguous chiral centers and broad distribution of molecular shapes via desymmetrization of the oxidative dearomatization products of phenols following a formal Pictet-Spingler/Aza-Michael addition cascade. These novel heterocyclic systems were further transformed into spiro-oxindole systems in one step manner. 
     SUMMARY OF THE INVENTION 
     The present invention relates to compounds of general formula I and II, processes for their preparation, intermediates, stereoisomers, and the use of such novel compounds for different disease states including but not limited to, cell proliferative diseases and any diseases that are connected to the modulation of cellular metabolism and mitochondrial function. 
     Compounds of General Formula I 
     
       
         
         
             
             
         
       
     
     Wherein, 
     
       
         
         
             
             
         
       
     
     denotes a phenyl ring which may be unsubstituted or substituted with 1, 2, 3 or 4 substituents independently selected from a halogen atom, CN, R 3 , OR 3 , SR 3 , N(R 3 ) 2 , C(O)R 3 , C(O)OR 3 , NR 3 C(O)R 3 , C(O)NR 3 , SO 2 R 3 , NR 3 SO 2 R 3 , SO 2 N(R 3 ) 2 . 
     U 
     denotes —CH 2  or —O. 
     R 1    
     denotes halogen atom, R 3 , OR 3 , SR 3 , N(R 3 ) 2 , NR 3 C(O)R 3 , C(O)NR 3 , SO 2 R 3 , NR 3 SO 2 R 3 , SO 2 N(R 3 ) 2 . 
     R 2    
     denotes hydrogen, halogen atom, CN, R 3 , OR 3 , SR 3 , N(R 3 ) 2 , C(O)R 3 , C(O)OR 3 , NR 3 C(O)R 3 , C(O)NR 3 , SO 2 R 3 , NR 3 SO 2 R 3 , SO 2 N(R 3 ) 2 , CH 2 C(O)R 3 , CH 2 C(O)OR 3 , CH 2 NR 3 C(O)R 3 , CH 2 C(O)NR 3 , CH 2 SO 2 R 3 , CH 2 NR 3 SO 2 R 3 , CH 2 SO 2 N(R 3 ) 2 . 
     R 3  is independently hydrogen or an optionally substituted group selected from a C 1-6  aliphatic group, a monocyclic 3-8 membered saturated, partially unsaturated, or aryl ring having 0-4 heteroatoms independently selected from nitrogen, oxygen, or sulfur, or a bicyclic 8-10 membered saturated, partially unsaturated, or aryl ring having 0-5 heteroatoms independently selected from nitrogen, oxygen, or sulfur. 
     In another embodiment, R 3  is selected from the group consisting of: —CX 3 , —CHX 2 , and —CH 2 X, wherein X is chlorine, fluorine, bromine, or iodine. 
     The stereochemical relation between H a , H b , R 1  and R 2  is either in the form of pure enantiomers, diastereoisomers or racemic mixtures. 
     In one embodiment, R 1  is connected to its vicinal quaternary carbon in the ring E to form an alicyclic ring. 
     In another embodiment, R 1  is connected to its vicinal secondary carbon in the ring E to form an alicyclic ring. 
     In yet another embodiment, present invention provides a process for the preparation of compound of general formula I, the process comprising the steps of:
         i. Reacting a compound of formula III       

     
       
         
         
             
             
         
       
     
     wherein Wand U are as defined above in the general formula I 
     with compound of formula IV 
     
       
         
         
             
             
         
       
     
     in the presence of TFA in a ratio ranging between 1:1 to 1:2 in a suitable aprotic solvent at a temperature in the range of −100° C. to rt for a period in the range of 2 to 12 h to obtain the compound of general formula V. 
     
       
         
         
             
             
         
       
         
         
           
             ii. Reacting a compound of general formula V with Pd/C in any suitable solvent under the hydrogen atmosphere at rt for a period in the range of 0.5 to 6 h to obtain compound of general formula I 
           
         
       
    
     
       
         
         
             
             
         
       
     
     Compounds of General Formula II 
     
       
         
         
             
             
         
       
     
     Wherein, 
     
       
         
         
             
             
         
       
     
     U, R 1  and R 2  are defined as above in the general formula I 
     In another embodiment, present invention provides a process for the preparation of compound of general formula II, which comprises of: 
     Reacting a compound of general formula I with NBS in a ratio ranging between 1:1 to 1:2 in THF:AcOH:H 2 O (1:1:1) at a temperature in the range of 0° C. to 50° C. for a period in the range of 1 to 6 h to obtain a compound of general formula II. 
     In yet another embodiment, present invention provides a process for the preparation of compound of general formula VI, which comprises of: 
     Reacting a compound of general formula V with NBS in a ratio ranging between 1:1 to 1:2 in THF:AcOH:H 2 O (1:1:1) at a temperature in the range of 0° C. to 50° C. for a period in the range of 1 to 6 h to obtain a compound of general formula VI. 
     
       
         
         
             
             
         
       
     
     Necessary starting materials for the preparation of compounds of general formula III and IV may be obtained by standard procedures of organic chemistry and some of them are commercially available. In addition, they are obtainable by analogous procedures to those illustrated which are within the ordinary skill of an organic chemist. 
     In an even further embodiment, the invention also provides pharmaceutical compositions comprising compounds of general formula I, II, V and VI. 
     In another aspect, the present invention provides a method of treating cancer by administering an effective amount of a compound or pharmaceutical composition of this invention. 
     In yet another aspect, the present invention provides a method to analyze the cellular ATP content in a biological system by administering to the subject or contacting the biological system with an effective amount of a compound of invention. 
     In yet another aspect, the present invention describes a method to analyze the mitochondrial membrane potential in a biological system by administering to the subject or contacting the biological system with an effective amount of a compound of invention. 
     In yet another aspect, the present invention describes a method to analyze the cellular redox potential in a biological system by administering to the subject or contacting the biological system with an effective amount of a compound of invention. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Diagram illustrating the method of preparation of compounds of formula I and V according to the invention are shown below. 
     
       
         
         
             
             
         
       
     
     Diagrams illustrating the method of preparation of compound of formula II and VI according to the invention are shown below. 
     
       
         
         
             
             
         
       
     
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  Screening of a pilot library on cellular functions in Hepa1-6. a Effect of compounds 1d and 1q on ATP. b Effect of compounds 1d and 1q on mitochondrial membrane potential. c Effect of compounds 1d and 1 q on cellular redox potential. d Effect of compounds 1d and 1 q on cellular proliferation. e Cytotoxicity of compounds 1d and 1q. Error bars indicate standard deviation based on three replicated calculations. Significance was tested using an ANOVA test, with Dunnett&#39;s multiple comparison test. 
         FIG. 2  Screening of a pilot library on cellular functions in Hepa1-6. a Effect of compounds 1d and 1q on immune cell proliferation in lymphocytes or isolated T cells. a-b Effect of compounds 1d and 1q on CD3 +  T lymphocytes. c-d Effect of compounds 1d and 1q on B220 +  B lymphocytes. e-f Effect of compounds 1d and 1q on isolated T cells. Error bars indicate standard deviation based on three replicated calculations. Significance was tested using an ANOVA test, with Dunnett&#39;s multiple comparison test. *p&lt;0.05 
     
    
    
     DEFINITIONS 
     The present invention relates to a novel process for the preparation of compounds of general formula I, II, V and VI, when discussing such compounds and their applications the following terms have the following meaning unless otherwise indicated. 
     The term “aryl” means an aromatic, or partially aromatic hydrocarbon group containing 6 to 10 carbon atoms and consisting of one or two rings which may be fused to each other or attached to each other via a single bond. Examples are phenyl, napthyl, biphenyl or indenyl. 
     The term “heteroaryl”, as used herein, means an aromatic or partially aromatic group consisting of one or two rings, which may be fused to each other or attached to each other via a single bond, and containing 5 to 10 ring atoms wherein up to four, preferably one, two or three ring atoms are heteroatom(s) and the remaining ring atoms are carbon. Examples of suitable heteroaryl groups include, but are not limited to, pyrrolyl, furyl, thienyl, oxazolyl, imidazolyl, purazolyl, isoxazolyl, isothiazolyl, triazolyl, thiadiazolyl, pyridyl, pyridazinyl, pyrimidinyl, pyrazinyl, pyranyl, furazanyl, indolizinyl, indolyl, isoindolinyl, indazolyl, benzofuryl, benzothienyl, benzimidazolyl, benzthiazolyl, purinyl, quinolizinyl, quinolinyl, isoquinolinyl, isothiazolyl, cinnolinyl, phthalazinyl, quinazolinyl, quinoxalinyl, naphthyridinyl, pteridinyl, and the like. 
     The term “alicyclic” means a saturated or unsaturated aliphatic cyclic ring system consisting of one or more rings, which may be fused to each other or attached to each other via a single bond, and containing 5 to 10 ring atoms more preferably carbons. Examples are cyclopentane, cyclohexane, cycloheptane, cyclooctane, terpene. 
     The term “alkyl”, as used herein, denotes a saturated, linear- or branched chain hydrocarbon group containing 1 to 8, preferably 1 to 6, more preferably 1 to 4 carbon atoms, for example methyl, ethyl, propyl, isopropyl, 1-butyl, 2-butyl, tert-butyl and the like. Preferred “C1-C8 alkyl” groups have 1, 2 or 3 carbon atoms. 
     The term “halogen” means fluorine, chlorine, bromine or iodine. 
     The term “substituted” means a group which may be substituted one to three times by halogen atom, CN, R 3 , OR 3 , SR 3 , N(R 3 ) 2 , C(O)R 3 , C(O)OR 3 , NR 3 C(O)R 3 , C(O)NR 3 , SO 2 R 3 , NR 3 SO 2 R 3 , SO 2 N(R 3 ) 2 . With reference to substituents, the term “independently” means that when more than one of such substituents is possible, such substituents may be the same or different from each other. 
     The term “pharmaceutically acceptable salt” refers to conventional acid-addition salts or base-addition salts that retain the biological effectiveness and properties of the compounds of formula I, II, V and VI and are formed from suitable non-toxic organic or inorganic acids or organic or inorganic bases. Acid-addition salts include for example those derived from inorganic acids such as hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, sulfamic acid, phosphoric acid and nitric acid, and those derived from organic acids such as p-toluenesulfonic acid, salicylic acid, methanesulfonic acid, oxalic acid, succinic acid, citric acid, malic acid, lactic acid, fumaric acid, and the like. Base-addition salts include those derived from ammonium, potassium, sodium and, quaternary ammonium hydroxides, such as for example, tetramethyl ammonium hydroxide. 
     The compounds of the invention can possess one or more asymmetric carbon atoms and are thus capable of existing in the form of optical isomers as well as in the form of racemic or non-racemic mixtures thereof. The compounds of the invention can be utilized in the present invention as a single isomer or as a mixture of stereochemical isomeric forms. Diastereoisomers, i.e., non superimposable stereochemical isomers, can be separated by conventional means such as chromatography, distillation, crystallization or sublimation. The optical isomers can be obtained by resolution of the racemic mixtures according to conventional processes, for example by formation of diastereoisomeric salts by treatment with an optically active acid or base. Examples of appropriate acids include, without limitation, tartaric, diacetyltartaric, dibenzoyltartaric, ditoluoyltartaric and camphorsulfonic acid. The mixture of diastereomers can be separated by crystallization followed by liberation of the optically active bases from these salts. An alternative process for separation of optical isomers includes the use of a chiral chromatography column optimally chosen to maximize the separation of the enantiomers. 
     The present invention also relates to the use of those active ingredients in the preparation of medicaments. In general, compounds of formula I, II, V and VI are administered either individually, or in combination with any other desired therapeutic agent, using the known and acceptable methods. Such therapeutically useful agents may be administered, for example, by one of the following routes: orally, for example in the form of dragees, coated tablets, pills, semi-solid substances, soft or hard capsules, solutions, emulsions or suspensions; parenterally, for example in the form of an injectable solution; rectally in the form of suppositories; by inhalation, for example in the form of a powder formulation or a spray; trans-dermal or intranasally. For the preparation of such tablets, pills, semi-solid substances, coated tablets, dragees and hard gelatine capsules, the therapeutically usable product may be mixed with pharmacologically inert, inorganic or organic pharmaceutical carrier substances, for example with lactose, sucrose, glucose, gelatine, malt, silica gel, starch or derivatives thereof, talcum, stearic acid or salts thereof, skimmed milk powder, and the like. For the preparation of soft capsules, pharmaceutical carrier substances such as, for example, vegetable oils, petroleum, animal or synthetic oils, wax, fat and polyols may be used. For the preparation of liquid solutions and syrups, pharmaceutical carrier substances such as, for example, water, alcohols, aqueous saline solution, aqueous dextrose, polyols, glycerol, vegetable oils, petroleum and animal or synthetic oils may be used. For suppositories, pharmaceutical carrier substances such as, for example, vegetable oils, petroleum, animal or synthetic oils, wax, fat and polyols may be used. For aerosol formulations, compressed gases that are suitable for this purpose, such as, for example, oxygen, nitrogen and carbon dioxide may be used. The pharmaceutically acceptable agents may also comprise additives for preserving and stabilizing, emulsifiers, sweeteners, flavourings, salts for altering the osmotic pressure, buffers, encapsulation additives and antioxidants. 
     The term “cancer” refers to a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. 
     The term “anticancer” defines the use of natural/synthetic methods/substances for effective health care that contribute to/prevent the uncontrolled proliferation of tumor cells. 
     The term “proliferative” or “proliferation” in biological conditions points un-controlled multiplication because of failure in of normal functions of a system or even a cell in the context of present invention. 
     The term “drug” refers to a natural or synthetic substance which (when taken into a living body) affects its functioning or structure, and is used in the diagnosis, mitigation, treatment, or prevention of a disease or relief of discomfort. 
     The term “effective amount” when used in connection with a compound of general formula I, II, V and VI means an amount of the subject compound effective for treating or preventing cancer or any other diseases. 
     The word “mitochondria” coins to an organelle present mainly in eukaryotic organism that often refers to the metabolic center for life activities of a cell and provides energy for the cell. 
     As used herein, the following abbreviations have the below meanings. 
     rt=Room temperature 
     TFA=Trifluroacetic acid 
     NBS=N-bromosuccinamide 
     Na 2 SO 4 =Sodium sulfate 
     EtOAc=Ethylacetate 
     DCM=Dicholoromethane 
     MeOH=Methanol 
     THF=Tetrahydrofuran 
     AcOH=Acetic acid 
     NMR=Nuclear magnetic resonance 
     HRMS=High resolution mass spectroscopy 
     LCMS=Liquid chromatography-mass spectroscopy 
     ESI-TOF=Electrosprayionization-time of flight 
     h=hours 
     ATP=Adenosine Tri-Phosphate 
     Pd/C=Palladium-Carbon 
     General Material and Methods 
     Chemistry 
     Chemical reagents and anhydrous solvents were purchased from Sigma-Aldrich and were used without further purification. Solvents for extraction and column chromatography were distilled prior to use. TLC analysis was performed with silica gel plates (0.25 mm, E. Merck, 60 F 254 ) using iodine and a UV lamp for visualization. Retention factor (R f ) values were measured using a 5×2 cm TLC plate in a developing chamber containing the solvent system described. Melting points were measured with a Stuart Melting Point Apparatus (SMP30) in Celsius degrees and were uncorrected.  1 H and  13 C NMR experiments were performed on a 500 MHz instrument. Chemical shifts are reported in parts per million (ppm) downstream from the internal tetramethylsilane standard. Spin multiplicities are described as s (singlet), d (doublet), dd (double doublets), t (triplet), (td) triple doublets or m (multiplet). Coupling constants are reported in Hertz (Hz). ESI mass spectrometry was performed on a Q-TOF high-resolution mass spectrometer or Q-TOF Ultim LC-MS. Optical rotations were measured with a digital polarimeter using a 100 mm cell of 10 mL capacity. 
     Biology 
     Chemicals and Cell Culture 
     The tested compounds were dissolved in DMSO at a concentration of 100 mM and further diluted in PBS supplemented with 10% (v/v) DMSO. When necessary dissolution was enhanced by incubation at 50° C. and sonication at maximum output for 10 min. Hepa1.6 cell line (#CRL-1830, ATCC) was cultured in DMEM culture medium containing 1 g L −1  glucose, 10% fetal bovine serum, 2 mM glutamine, 100 U mL −1  Penicillin and 100 μg mL −1  Streptomycin and 30 μM oleic acid. Cells were seeded at a density of 20000 cells per well in 96 well plates and incubated for several hours to allow the cells to attach at 37° C. with 5% CO 2 . Cells were then supplemented with the test substances at indicated concentrations (0.01-50 μM) and incubated for indicated time periods (24-48 h). 
     For all assays the tested substances were further diluted in 10% DMSO/PBS and added to the cells at the indicated concentrations with a final DMSO concentration of 0.01%. Negative vehicle controls were treated with 0.01% DMSO. Positive control was treated with 10 μM oligomycin or 10 μM FCCP (Carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone). 
     Cytotoxicity 
     Cytotoxicity was assessed using the Pierce LDH Cytotoxicity Assay Kit (#88953, Thermo Fisher). After cells were culture with the test substances for 24 h 20 μL of the cell culture medium were transferred to a new 96 well plate and the cytotoxicity assay was performed as per the manufacturer&#39;s instructions. Absorbance was measure at 490 nm and background at 680 nm. The signal intensity of untreated cells was considered as the background signal of spontaneous LDH release and subtracted from all measurements. Cytotoxicity was expressed as the percentage of maximum signal intensity observed in freshly lysed cells. 
     Mitochondrial Membrane Potential 
     Mitochondrial membrane potential (ΔΨm) was assessed using the tetramethylrhodamine (TMRE) fluorophore. The cells were incubated with the test substances for 24 h and then loaded with TMRE at a final concentration of 200 nM for 45 min at 37° C. Positive control wells were treated with 10 μM FCCP 30 min before loading the cells with TMRE. The medium was removed and the cells were washed with PBS and supplemented with fresh culture medium. Fluorescence intensity of TRME was immediately measured (ex/em: 545/580 nm) using a plate reader spectrophotometer. The results were normalized to the fluorescence intensity measured in mock treated negative controls and the positive controls treated with 10 μM FCCP. 
     ATP Content 
     Cells were treated for 24 h with the test substances at the indicated concentrations. The cellular ATP content was assessed using the CellTiter-Glo Assay (#G7571, Promega) as per the manufacturer&#39;s instructions. Luminescence was detected in a plate reader spectrophotometer. The results were normalized to the luminescence intensity measured in mock treated negative controls and the positive controls treated with 10 μM oligomycin. 
     Cellular Re Dox Potential 
     Cells were treated for 24 h with the test substances or controls (0.1% DMSO, 10 μM FCCP and 10 μM oligomycin). AlamarBlue reagent (resazurin, #BUF012A, Bio-Rad) was added to the cells in an amount equal to 10% of the culture medium per well during the last 4 h of incubations. Fluorescence was measured at ex/em: 550/590 nm. Results were normalized to the fluorescence intensity measured in blank wells and wells containing fully reduced AlamarBlue reagent. Results were expressed relative to the mock treated negative controls. 
     BrdU Incorporation/Cell Proliferation Assay Proliferation 
     Cells were incubated for a total of 48 h with the tested substances. During the last 12 h the cells were supplemented with 200 μM BrdU (#ab126556, Abcam). After the incubation period cells were washed with PBS. Following that the cells fixed and permeabilized using the reagents of the kit and labeled for 1 h with anti-BrdU antibodies conjugated with peroxidase. After washing the fixed cells 5 times with PBS the wells were incubated with peroxidase substrate TMB. The reaction was stopped after 30 min. The signal intensity was measure at absorbance 450 nm. Results were normalized to controls samples treated with vehicle (0.01% DMSO, negative control) or 10 μM oligomycin. 
     Lymphocyte and Splenocyte Preparation 
     Spleen and lymph nodes were collected from C57BL/6J mice and stored in RPMI medium on ice until further processing. Further procedures were performed using a laminar flow hood. Single cell suspensions were created by shearing the organs between two microscopy slides. Cell suspensions were passed through a 70 μm cell strainer to exclude remaining tissue chunks. Cells were washed in PBS and centrifuged at 300 g for 5 min at 4° C. During the preparation of splenic single cell suspension, erythrocytes were removed by incubating the cells for 5 min at rt in RBC lysis buffer followed by extensive washing in PBS. Cells were resuspended in RPMI medium and cell count was determined. Lymphocytes were kept on ice until further use. 
     T Cell Enrichment from Splenocytes 
     T cell was enriched from the splenocytes by negative selection using magnetic bead separation (Pan T cell isolation kit II, mouse, #130-095-130, Miltenyi) achieving more than 90% purity. The cells were kept in RPMI medium until further use. 
     Activation Induced Immune Cell Proliferation in T Cells and Lymphocytes 
     A total 17×10 6  cells were suspended in 15 mL Krebs Ringer buffer (with HEPES, 1 g L −1  glucose, 1 mM pyruvate), supplemented with 30 μL of Cytopainter blue stock solution (500×) (#ab176726, Abcam) and incubated for 30 min at 37° C. to let the CFSE analog accumulate in the cells. The remaining Cytopainter reagent that was not incorporated into the cells was quenched by addition of 10 mL FCS and incubated for 5 min at rt. Another 25 mL of PBS were added and cells were centrifuged at 300 g for 5 min at rt. The cells were then suspended in 12.75 mL of complete RPMI culture medium. 2×10 5  cells in a volume of 150 μL were added to the wells of 96 well plates. The cytopainter-loaded cells were supplemented with the test substances, or DMSO as a negative control and oligomycin as a positive control. 
     Cytopainter loaded T cells were stimulated using two different approaches. Either T cells stimulated by plate bound anti-CD3 antibodies (coated at 1 μg/mL) and soluble anti-CD28 antibodies (at a final concentration of 0.2 μg mL −1 ), or in separate replicates by addition of the cytokines IL-2 (50 ng mL −1 ) and IL-7 (10 ng mL −1 ) to stimulate T cells proliferation and survival. 
     Cytopainter loaded lymphocytes were stimulated with PMA (15 ng mL −1 ) and Ionomycin (0.5 μg mL −1 ). All cells were incubated for 60 h at 37° C., 5% CO 2 . Lymphocytes were then washed with 2% FBS in PBS, supplemented with anti-CD16/CD32 antibodies (to block unspecific Fc-receptor binding) and incubated for 10 min at 4° C. Subsequently cells were incubated for 20 min at 4° C. with anti-CD3 antibodies conjugated to FITC (clone: 145-2C11, #11-0031-82, eBioscience) and anti-B220 antibodies conjugated to PerCP-Cy5.5 (clone:RA3-6B2, #45-0452-82, eBioscience) to label T cells and B cells, respectively. Cells were subsequently washed with 2% FBS in PBS analyzed. 
     Cell proliferation was then analyzed by assessing the fluorescence intensity of cytopainter in the cells by flow cytometry. Reduced intensity of cytopainter dye indicates cells that have undergone cell division. Data was analyzed using FlowJo v10.4.2. Proliferation parameters were derived using the FlowJo Proliferation Tool. The Expansion index determines the fold-expansion of the overall culture. The Division index expresses the average number of cell divisions that a cell in the original population has undergone and also includes the cells that have never divided. 
     Statistical analysis was performed using Graph Pad Prism v6.07. Comparison of the test substances was performed by ANOVA with Dunnett&#39;s post hoc test unless otherwise stated. Non-linear regression was fitted to the data points using Graph Pad. 
     Example-1 
     It describes the process for the preparation of compounds of general formula V and the characterization data for the selected compounds of this class. 
     Aldehyde (III, 0.5 mmol) was dissolved in DCM (2 mL) and a solution of amine (IV, 0.5 mmol) in DCM (2.0 mL) was added dropwise at −78° C. Then, a solution of TFA (1.0 mmol) in DCM (1 mL) was added dropwise at −78° C. and slowly warmed to room temperature and stirring was continued for 2-4 h. After completion, the reaction mixture was diluted with DCM (30 mL) and washed with saturated sodium bicarbonate solution (2×20 mL). The organic layer was separated, dried over Na 2 SO 4  and concentrated under vacuum. The crude was purified on flash chromatography, using EtOAc/hexane as an eluent to produce the compounds of general formula V. 
     
       
         
         
             
             
         
       
     
     (2aR,6aR,14bS)-2a-Methoxy-2,2a,6,6a,8,9,14,14b-octahydroindolo[2′,3′:3,4] pyrido[1,2-a]quinolin-5(1H)-one (1a) 
     Off-white solid, 107 mg, 67% yield; mp: 204-207° C.; R f =0.45 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, CDCl 3 ): δ 7.79 (s, 1H), 7.48 (t, J=7.6 Hz, 1H), 7.31 (t, J=8.4 Hz, 1H), 7.19-7.09 (m, 2H), 6.86 (d, J=10.3 Hz, 1H), 6.12 (d, J=10.3 Hz, 1H), 3.96 (d, J=10.0 Hz, 1H), 3.83-3.74 (m, 1H), 3.32 (s, 3H), 3.11-3.05 (m, 1H), 3.03-2.90 (m, 2H), 2.85-2.73 (m, 3H), 2.09-1.97 (m, 2H), 1.95-1.83 (m, 2H);  13 C NMR (125 MHz, CDCl 3 ): δ 199.4, 155.5, 136.2, 134.5, 130.6, 127.3, 121.5, 119.5, 118.2, 110.7, 108.6, 74.7, 59.1, 50.7, 50.4, 49.3, 35.3, 30.3, 24.9, 22.1; HRMS (m/z): [M+H] +  calcd. for C 20 H 23 N 2 O 2 , 323.1759; found 323.1764. 
     
       
         
         
             
             
         
       
     
     (2 aR,6aR,14bS)-2a, 11-Dimethoxy-2,2a,6,6a,8,9,14,14b-octahydroindolo[2′,3′:3,4]pyrido[1,2-a]quinolin-5(1H)-one (1b) 
     Off-white solid, 121 mg, 69% yield; mp: 216-218° C.; R f =0.4 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, CDCl 3 ): δ 7.67 (s, 1H), 7.21 (d, J=8.7 Hz, 1H), 6.94 (d, J=2.0 Hz, 1H), 6.88-6.79 (m, 2H), 6.11 (d, J=10.3 Hz, 1H), 3.92 (d, J=10.7 Hz, 1H), 3.87 (s, 3H), 3.77 (t, J=8.6 Hz, 1H), 3.33 (s, 3H), 3.11-3.04 (m, 1H), 3.02-2.86 (m, 2H), 2.80 (d, J=8.6 Hz, 2H), 2.72 (d, J=14.3 Hz, 1H), 2.10-1.96 (m, 2H), 1.93-1.80 (m, 2H);  13 C NMR (125 MHz, CDCl 3 ): δ 199.3, 155.5, 154.1, 135.4, 131.2, 130.6, 127.7, 111.4, 111.2, 108.5, 100.5, 74.7, 59.1, 55.9, 50.7, 50.5, 49.3, 35.3, 30.4, 24.9, 22.2; HRMS (m/z): [M+H] +  calcd. for C 21 H 25 N 2 O 3 , 353.1865, found 353.1871. 
     
       
         
         
             
             
         
       
     
     (2aS,6aR,14bS)-2a-methyl-6,6a,8,9,14,14b-hexahydro-1H-benzo[5′,6′][1,4]oxazino[4′,3′:1,2]pyrido[3,4-b]indol-5(2aH)-one (1c) 
     White solid, 32 mg, 21% yield; mp: 226-228° C.; R f =0.5 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, CDCl 3 ): δ 7.66 (s, 1H), 7.48 (d, J=7.8 Hz, 1H), 7.31 (d, J=8.0 Hz, 1H), 7.19-7.13 (m, 1H), 7.11 (dd, J=11.0, 3.9 Hz, 1H), 6.64 (dd, J=10.1, 2.1 Hz, 1H), 6.06 (d, J=10.1 Hz, 1H), 4.09 (d, J=7.9 Hz, 1H), 3.81-3.71 (m, 2H), 3.54 (dd, J=11.3, 4.5 Hz, 1H), 3.11-3.02 (m, 2H), 2.89-2.79 (m, 1H), 2.79-2.67 (m, 2H), 2.34 (td, J=11.3, 3.9 Hz, 1H), 1.58 (s, 3H);  13 C NMR (125 MHz, CDCl 3 ): δ 196.7, 153.2, 136.2, 130.4, 130.2, 127.0, 121.9, 119.7, 118.3, 110.8, 110.1, 74.7, 66.3, 66.1, 58.4, 46.1, 40.1, 25.6, 22.0; HRMS (m/z): [M+H] +  calcd. for C 19 H 21 N 2 O 2 , 309.1603, found 309.1611. 
     
       
         
         
             
             
         
       
     
     (2aS,6aR,14bR)-2a-Methyl-6,6a,8,9,14,14b-hexahydro-1H-benzo[5′,6′][1,4]oxazino[4′,3′:1,2]pyrido[3,4-b]indol-5(2 aH)-one (1d) 
     White solid, 80 mg, 52% yield; mp: 217-219° C.; R f =0.45 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, CDCl 3 ): δ 7.95 (s, 1H), 7.52 (d, J=7.7 Hz, 1H), 7.36 (d, J=8.0 Hz, 1H), 7.23-7.17 (m, 1H), 7.17-7.12 (m, 1H), 6.70 (d, J=10.6 Hz, 1H), 6.13 (d, J=10.6 Hz, 1H), 4.27-4.14 (m, 2H), 4.10-4.01 (m, 1H), 3.32 (d, J=4.4 Hz, 2H), 3.09-2.93 (m, 3H), 2.72 (d, J=14.9 Hz, 1H), 2.64 (dd, J=16.0, 3.5 Hz, 1H), 1.51 (s, 3H);  13 C NMR (125 MHz, CDCl 3 ): δ  13 C NMR (125 MHz, CDCl 3 ) δ 198.9, 151.4, 136.1, 130.8, 129.9, 127.3, 121.9, 119.7, 118.1, 111.0, 109.7, 72.2, 63.5, 59.0, 52.1, 48.0, 46.1, 23.6, 19.3; HRMS (m/z): [M+H] +  calcd. for C 19 H 21 N 2 O 2 , 309.1603, found 309.1607. 
     
       
         
         
             
             
         
       
     
     (2aS,6aR,14bS)-11-Methoxy-2a-methyl-6,6a,8,9,14,14b-hexahydro-1H-benzo[5′,6′][1,4]oxazino[4′,3′:1,2]pyrido[3,4-b]indol-5(2aH)-one (1e) 
     Off-white solid, 34 mg, 20% yield; mp: 243-246° C.; R f =0.4 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, CDCl 3 ): δ 7.54 (s, 1H), 7.20 (d, J=8.7 Hz, 1H), 6.92 (d, J=1.9 Hz, 1H), 6.81 (dd, J=8.7, 2.4 Hz, 1H), 6.64 (d, J=9.8 Hz, 1H), 6.05 (d, J=10.3 Hz, 1H), 4.07 (d, J=6.9 Hz, 1H), 3.85 (s, 3H), 3.75 (d, J=5.9 Hz, 2H), 3.53 (dd, J=11.2, 5.2 Hz, 1H), 3.05 (d, J=13.5 Hz, 2H), 2.86-2.74 (m, 3H), 2.38-2.30 (m, 1H), 1.57 (s, 3H);  13 C NMR (125 MHz, CDCl 3 ): δ 196.7, 154.2, 153.2, 131.3, 130.4, 130.3, 127.5, 111.8, 111.5, 110.0, 100.4, 74.7, 66.3, 66.0, 58.5, 55.9, 46.2, 40.1, 25.6, 22.0; HRMS (m/z): [M+H] +  calcd. for C 20 H 23 N 2 O 3 , 339.1708, found 339.1715. 
     
       
         
         
             
             
         
       
     
     (2aS,6aR,14bR)-11-methoxy-2a-methyl-6,6a,8,9,14,14b-hexahydro-1H-benzo[5′,6′][1,4]oxazino[4′,3′:1,2]pyrido[3,4-b]indol-5(2aH)-one (1f) 
     Off-white solid, 89 mg, 53% yield; mp: 230-232° C.; R f =0.4 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, CDCl 3 ): δ 7.73 (s, 1H), 7.24 (d, J=8.7 Hz, 1H), 6.97 (d, J=1.7 Hz, 1H), 6.85 (dd, J=8.7, 2.1 Hz, 1H), 6.70 (d, J=10.2 Hz, 1H), 6.12 (d, J=10.2 Hz, 1H), 4.22-4.09 (m, 2H), 4.00 (dd, J=11.4, 6.0 Hz, 1H), 3.88 (s, 3H), 3.29 (d, J=4.8 Hz, 2H), 3.09-2.90 (m, 3H), 2.70-2.59 (m, 2H), 1.52 (s, 3H);  13 C NMR (125 MHz, CD 3 OD): δ 199.9, 153.6, 152.6, 131.9, 131.7, 129.3, 127.3, 111.6, 110.8, 107.9, 99.9, 72.0, 63.1, 58.8, 55.5, 53.3, 52.4, 35.6, 23.1, 18.9; HRMS (m/z): [M+H] +  calcd. for C 20 H 23 N 2 O 3 , 339.1708, found 339.1719. 
     
       
         
         
             
             
         
       
     
     Methyl (2aR,6aR,8S,14bS)-2a-methoxy-5-oxo-1,2,2a,5,6,6a,8,9,14,14b-decahydroindolo[2′,3′:3,4]pyrido[1,2-a]quinoline-8-carboxylate (1g) 
     Pinkish solid, 120 mg, 63% yield; mp: 159-161° C.; R f =0.4 (silica gel, hexane/EtOAc 1:2); [α] D =−275.0 (0.0047 M in acetone);  1 H NMR (500 MHz, CDCl 3 ): δ 7.86 (s, 1H), 7.44 (d, J=7.7 Hz, 1H), 7.33 (d, J=8.0 Hz, 1H), 7.21-7.08 (m, 2H), 6.85 (d, J=10.3 Hz, 1H), 6.10 (d, J=10.3 Hz, 1H), 4.01 (d, J=11.3 Hz, 1H), 3.93 (dd, J=10.6, 7.2 Hz, 1H), 3.83 (s, 3H), 3.75 (dd, J=10.6, 3.9 Hz, 1H), 3.37 (s, 3H), 3.19-3.12 (m, 1H), 3.05-2.99 (m, 1H), 2.85-2.75 (m, 2H), 2.17-1.98 (m, 3H), 1.92-1.81 (m, 1H);  13 C NMR (125 MHz, CDCl 3 ): δ 198.6, 173.1, 156.6, 136.3, 133.2, 130.9, 126.9, 122.0, 119.9, 118.2, 110.9, 106.4, 74.8, 60.9, 54.8, 52.4, 51.0, 50.4, 34.0, 30.7, 27.1, 25.9; HRMS (m/z): [M+H] +  calcd. for C 22 H 25 N 2 O 4 , 381.1814, found 381.1815. 
     
       
         
         
             
             
         
       
     
     Methyl (2 aR,6aR,8R,14bS)-2a-methoxy-5-oxo-1,2,2a, 5,6,6a, 8,9,14,14b-decahydroindolo[2′3′:3,4]pyrido[1,2-c)]quinoline-8-carboxylate (1h) 
     Off-white solid, 104 mg, 55% yield; mp: 158-160° C.; R f =0.4 (silica gel, hexane/EtOAc 1:2); [α] D =+280.7 (0.0034 M in acetone);  1 H NMR (500 MHz, CDCl 3 ): δ 8.09 (s, 1H), 7.43 (d, J=7.8 Hz, 1H), 7.36 (d, J=8.0 Hz, 1H), 7.16 (t, J=7.3 Hz, 1H), 7.10 (t, J=7.4 Hz, 1H), 6.83 (d, J=10.3 Hz, 1H), 6.08 (d, J=10.3 Hz, 1H), 3.92 (dd, J=10.8, 6.2 Hz, 2H), 3.83 (s, 3H), 3.72 (dd, J=10.6, 3.8 Hz, 1H), 3.35 (s, 3H), 3.19-3.11 (m, 1H), 3.02 (dd, J=14.8, 2.6 Hz, 1H), 2.79-2.68 (m, 2H), 2.11-1.93 (m, 3H), 1.85-1.71 (m, 2H);  13 C NMR (125 MHz, CDCl 3 ): δ 198.6, 173.0, 156.6, 136.3, 133.3, 130.8, 126.9, 121.9, 119.8, 118.2, 111.0, 106.2, 74.8, 60.9, 54.8, 52.4, 51.0, 50.4, 34.0, 30.6, 27.1, 25.9; HRMS (m/z): [M+H] +  calcd. for C 22 H 25 N 2 O 4 , 381.1814, found 381.1823. 
     
       
         
         
             
             
         
       
     
     Methyl (2 aR,6aR,8S, 14bS)-11-hydroxy-2a-methoxy-5-oxo-1,2,2a, 5,6,6a, 8,9,14,14b-decahydroindolo[2′3′:3,4]pyrido[1,2-c)]quinoline-8-carboxylate (1i) 
     Brownish solid, 79 mg, 40% yield; mp: 165-167° C.; R f =0.35 (silica gel, hexane/EtOAc 1:2); [α] D =−214.2 (0.0017 Min acetone);  1 H NMR (500 MHz, CD 3 OD): δ 7.13 (d, J=8.6 Hz, 1H), 6.90 (dd, J=10.4, 3.6 Hz, 1H), 6.76 (d, J=2.3 Hz, 1H), 6.64 (dd, J=8.6, 2.3 Hz, 1H), 6.05 (d, J=10.3 Hz, 1H), 3.95-3.86 (m, 1H), 3.87-3.79 (m, 4H), 3.69 (dd, J=10.5, 3.9 Hz, 1H), 3.31 (s, 3H), 3.04-2.95 (m, 1H), 2.95-2.82 (m, 2H), 2.72-2.63 (m, 1H), 2.13 (d, J=6.7 Hz, 1H), 1.99-1.84 (m, 3H);  13 C NMR (125 MHz, CD 3 OD): δ 199.5, 173.2, 156.5, 150.0, 134.4, 131.6, 129.8, 127.1, 110.9, 110.4, 103.7, 101.7, 74.9, 61.1, 55.2, 51.3, 50.4, 49.7, 33.5, 29.8, 26.4, 25.0; HRMS (m/z): [M+H] +  calcd. for C 22 H 25 N 2 O 5 , 397.1763, found 397.1774. 
     
       
         
         
             
             
         
       
     
     Methyl (2 aS,6aR,8S,14bR)-2a-methyl-5-oxo-2a,5,6,6a,8,9,14,14b-octahydro-1H-benzo[5′,6′][1,4]oxazino[4′,3′:1,2]pyrido[3,4-b]indole-8-carboxylate (1j) 
     Off-white solid, 78 mg, 43% yield; mp: 150-153° C.; R f =0.45 (silica gel, hexane/EtOAc 1:1); [α] D =−252.4 (0.0054 M in acetone);  1 H NMR (500 MHz, CDCl 3 ): δ 7.89 (s, 1H), 7.51 (d, J=7.7 Hz, 1H), 7.36 (d, J=8.0 Hz, 1H), 7.25-7.19 (m, 1H), 7.16 (dd, J=11.0, 3.9 Hz, 1H), 6.73 (d, J=10.2 Hz, 1H), 6.08 (d, J=10.2 Hz, 1H), 4.36-4.29 (m, 1H), 4.17 (dd, J=11.2, 2.8 Hz, 1H), 3.99 (dd, J=11.2, 9.1 Hz, 1H), 3.86-3.76 (m, 4H), 3.46-3.38 (m, 1H), 3.22-3.12 (m, 1H), 3.11-2.94 (m, 2H), 2.58 (dd, J=15.9, 3.7 Hz, 1H), 1.60 (d, J=10.6 Hz, 3H);  13 C NMR (125 MHz, CDCl 3 ): δ198.6, 172.8, 151.0, 136.4, 129.6, 126.8, 122.7, 120.1, 118.3, 111.2, 108.1, 76.9, 71.6, 64.0, 60.7, 56.9, 52.5, 52.0, 33.9, 25.0, 22.9; HRMS (m/z): [M+H] +  calcd. for C 21 H 23 N 2 O 4 , 367.1657, found 367.1660. 
     
       
         
         
             
             
         
       
     
     Methyl (2 aS,6aR,8R,14bR)-2a-methyl-5-oxo-2a,5,6,6a,8,9,14,14b-octahydro-1H-benzo[5′,6′][1,4]oxazino[4 ‘,3’:1,2]pyrido[3,4-b]indole-8-carboxylate (1k) 
     Off-white solid, 95 mg, 52% yield; mp: 150-152° C.; R f =0.45 (silica gel, hexane/EtOAc 1:1); [α] D =+250.0 (0.0027 M in acetone);  1 H NMR (500 MHz, Acetone-d 6 ): δ 10.06 (s, 1H), 7.46 (d, J=7.8 Hz, 1H), 7.32 (d, J=8.0 Hz, 1H), 7.11-7.05 (m, 1H), 7.05-6.99 (m, 1H), 6.72 (d, J=10.2 Hz, 1H), 5.93 (d, J=10.2 Hz, 1H), 4.36 (d, J=9.2 Hz, 1H), 4.27 (dd, J=11.2, 3.5 Hz, 1H), 3.89 (t, J=9.7 Hz, 1H), 3.83-3.74 (m, 4H), 3.35 (dd, J=11.4, 3.8 Hz, 1H), 3.13-2.93 (m, 2H), 2.81 (t, J=10.1 Hz, 1H), 2.53 (dd, J=15.5, 3.8 Hz, 1H), 1.59 (s, 3H);  13 C NMR (125 MHz, Acetone-d 6 ): δ 198.7, 173.3, 151.4, 137.7, 137.6, 131.3, 129.6, 127.7, 122.2, 119.9, 118.6, 111.9, 107.3, 71.7, 64.4, 61.5, 57.8, 52.4, 33.7, 30.3, 22.7; HRMS (m/z): [M+H] +  calcd. for C 21 H 23 N 2 O 4 , 367.1657, found 367.1649. 
     
       
         
         
             
             
         
       
     
     (2aS,9aR, 17bR)-3,4,5,6,9,9a, 11,12,17,17b-Decahydro-1H,8H-naphtho[1″,8a″:5′,6′][1,4]oxazino[4′,3′: 1,2]pyrido[3,4-b]indol-8-one (II) 
     White solid, 88 mg, 55% yield; mp: 232-235° C.; R f =0.45 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, CDCl 3 ): δ 7.83 (s, 1H), 7.52 (d, J=7.8 Hz, 1H), 7.34 (d, J=7.8 Hz, 1H), 7.22-7.09 (m, 2H), 5.91 (s, 1H), 4.16 (d, J=8.4 Hz, 1H), 4.05 (dd, J=10.6, 2.8 Hz, 1H), 3.84 (t, J=10.6 Hz, 1H), 3.21-3.12 (m, 2H), 3.12-3.02 (m, 1H), 3.11-2.92 (m, 3H), 2.80-2.70 (m, 1H), 2.68-2.51 (m, 2H), 2.36 (d, J=13.9 Hz, 1H), 1.94 (d, J=12.2 Hz, 1H), 1.73-1.57 (m, 2H), 1.53-1.39 (m, 1H), 1.21 (t, J=12.9 Hz, 1H);  13 C NMR (125 MHz, CDCl 3 ): δ 199.6, 162.5, 136.3, 130.7, 127.1, 125.2, 121.9, 119.7, 118.2, 110.9, 109.8, 72.5, 63.2, 60.6, 50.6, 48.9, 32.6, 32.2, 32.1, 26.9, 21.4, 20.2; HRMS (m/z): [M+H] +  calcd. for C 22 H 25 N 2 O 2 , 349.1916, found 349.1910. 
     
       
         
         
             
             
         
       
     
     (2aS,6aR,14bR)-8,9,14,14b-Tetrahydro-1H-2a,6a-propanobenzo[5′,6′][1,4]oxazino[4′,3′:1,2]pyrido[3,4-b]indol-5(6H)-one (1m) 
     Off-white solid, 50 mg, 30% yield; mp: 126-228° C.; R f =0.5 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, CDCl 3 ): δ 7.84 (s, 1H), 7.52 (d, J=7.5 Hz, 1H), 7.34 (d, J=7.5 Hz, 1H), 7.16 (dt, J=26.8, 7.2 Hz, 2H), 6.62 (t, J=12.2 Hz, 1H), 6.08 (d, J=10.1 Hz, 1H), 4.17-4.06 (m, 2H), 3.93 (t, J=10.6 Hz, 1H), 3.32 (d, J=7.3 Hz, 1H), 3.03 (d, J=15.6 Hz, 1H), 2.91-2.80 (m, 2H), 2.61-2.45 (d, J=14.3 Hz, 1H), 2.62-2.43 (m, 2H), 2.22 (t, J=9.7 Hz, 1H), 1.98-1.87 (m, 1H), 1.64-1.44 (m, 3H);  13 C NMR (125 MHz, CDCl 3 ) δ: 200.1, 150.4, 136.3, 130.9, 128.9, 127.0, 121.9, 119.7, 118.2, 110.9, 110.4, 80.3, 63.5, 62.5, 51.8, 43.1, 35.8, 33.8, 30.4, 22.6, 19.0; HRMS (m/z): [M+H] +  calcd. for C 21 H 23 N 2 O 2 , 335.1759, found 335.1754. 
     
       
         
         
             
             
         
       
     
     (2 aS,6aR,14bR)-8,9,14,14b-Tetrahydro-1H-2a,6a-propanobenzo[5′,6′][1,4]oxazino[4′,3′: 1,2]pyrido[3,4-b]indol-5(6H)-one (1n) 
     Off-white solid, 50 mg, 30% yield; mp: 200-202° C.; R f =0.55 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, CDCl 3 ): δ 7.72 (s, 1H), 7.53-7.41 (m, 1H), 7.36-7.25 (m, 1H), 7.19-7.06 (m, 2H), 6.67 (d, J=10.2 Hz, 1H), 6.08 (d, J=10.2 Hz, 1H), 4.15 (d, J=9.7 Hz, 1H), 4.06 (dd, J=10.8, 3.0 Hz, 1H), 3.69 (t, J=10.8 Hz, 1H), 3.47 (dd, J=11.3, 4.8 Hz, 1H), 2.94 (d, J=16.0 Hz, 1H), 2.85-2.74 (m, 1H), 2.67 (d, J=14.9 Hz, 1H), 2.60-2.47 (m, 2H), 2.41 (td, J=11.5, 3.4 Hz, 1H), 2.24-1.99 (m, 3H), 1.97-1.85 (m, 1H), 1.48-1.35 (m, 1H);  13 C NMR (125 MHz, CDCl 3 ): δ 197.8, 150.5, 136.2, 130.9, 130.8, 127.1, 121.7, 119.7, 118.2, 110.8, 110.2, 83.2, 71.5, 65.7, 51.9, 45.8, 43.5, 36.6, 25.7, 22.6, 20.5; HRMS (m/z): [M+H] +  calcd. for C 21 H 23 N 2 O 2 , 335.1759, found 335.1755. 
     Example 2 
     It describes the process for the preparation of compounds of general formula I and the characterization data for the selected compounds of this class. 
     Compound of general formula (V, 0.2 mmol) was dissolved in methanol (1.0 mL) and 10 wt % Pd/C (5 mol %) was added and stirring was continued under hydrogen atmosphere for 3-4 h at rt. After completion, the reaction mixture was filtered through a celite pad and the filtrate was concentrated. The crude was purified on flash chromatography, using EtOAc in hexane as an eluent to produce compounds of general formula I. 
     
       
         
         
             
             
         
       
     
     (2aR,6aR,14bS)-2a-Methoxy-2,2a, 3,4,6,6a,8,9,14,14b-decahydroindolo[2′,3′: 3,4]pyrido[1,2-a]quinolin-5(1H)-one (1o) 
     Off-white solid, 58 mg, 90% yield; mp: 183-185° C.; R f =0.45 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, CDCl 3 ): δ 7.86 (s, 1H), 7.48 (d, J=7.6 Hz, 1H), 7.35 (d, J=7.6 Hz, 1H), 7.20-7.09 (m, 2H), 4.29-4.21 (m, 1H), 3.48-3.36 (m, 1H), 3.28-3.21 (m, 4H), 3.05-2.96 (m, 1H), 2.87 (t, J=13.0 Hz, 2H), 2.62 (d, J=13.0 Hz, 2H), 2.53-2.37 (m, 2H), 2.36-2.27 (m, 1H), 2.15-2.05 (m, 2H), 2.03-1.88 (m, 2H), 1.70-1.59 (s, 1H);  13 C NMR (125 MHz, CDCl 3 ): δ 211.1, 135.9, 133.2, 127.8, 121.6, 119.7, 118.2, 110.9, 109.0, 73.6, 61.0, 53.5, 48.6, 48.2, 38.3, 37.2, 28.5, 27.3, 24.6, 18.8; HRMS (m/z): IM+Hr calcd. for C 20 H 25 N 2 O 2 , 325.1916, found 325.1908. 
     
       
         
         
             
             
         
       
     
     (2aR,6aR,14bS)-2a,11-dimethoxy-2,2a,3,4,6,6a,8,9,14,14b-decahydroindolo[2′,3′:3,4]pyrido[1,2-a]quinolin-5(1H)-one (1p) 
     Off-white solid, 67 mg, 95% yield; mp: 180-183° C.; R f =0.4 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, Acetone): δ 9.73 (s, 1H), 7.17 (t, J=10.1 Hz, 1H), 6.91 (d, J=2.4 Hz, 1H), 6.68 (dd, J=8.7, 2.4 Hz, 1H), 4.21-4.12 (m, 1H), 3.78 (s, 3H), 3.30 (dd, J=12.8, 4.6 Hz, 1H), 3.24-3.17 (m, 4H), 2.95-2.88 (m, 1H), 2.85-2.69 (m, 3H), 2.64 (dd, J=13.8, 7.0 Hz, 1H), 2.55-2.49 (m, 1H), 2.38-2.30 (m, 1H), 2.25 (dt, J=16.0, 5.3 Hz, 2H), 2.18-2.12 (m, 1H), 2.11-2.07 (m, 1H), 1.91 (dd, J=12.3, 6.3 Hz, 1H), 1.59-1.50 (m, 1H);  13 C NMR (125 MHz, Acetone): δ 209.6, 154.8, 136.1, 132.3, 128.9, 112.3, 111.3, 108.3, 100.7, 74.3, 61.8, 55.8, 54.0, 48.9, 48.4, 38.6, 37.7, 29.2, 28.2, 25.1, 20.1; HRMS (m/z): [M+H] +  calcd. for C 21 H 27 N 2 O 3 , 355.2021, found 355.2029. 
     
       
         
         
             
             
         
       
     
     (2aS,6aR,14bR)-2a-Methyl-3,4,6,6a,8,9,14,14b-octahydro-1H-benzo[5′,6′][1,4]oxazino[4′,3′:1,2]pyrido[3,4-k]indol-5(2aH)-one (1q) 
     Off-white solid, 57 mg, 92% yield; mp: 236-238° C.; R f =0.5 (silica gel, hexane/EtOAc 1:1);  1 H NMR (500 MHz, CDCl 3 ): δ 7.74 (s, 1H), 7.49 (d, J=7.7 Hz, 1H), 7.32 (d, J=7.9 Hz, 1H), 7.16 (t, J=7.4 Hz, 1H), 7.11 (t, J=7.3 Hz, 1H), 4.17-4.05 (m, 2H), 3.89 (t, J=10.6 Hz, 1H), 3.13-3.02 (m, 2H), 3.01-2.91 (m, 1H), 2.90-2.81 (m, 2H), 2.81-2.67 (m, 2H), 2.44 (d, J=9.2 Hz, 1H), 2.19 (d, J=11.9 Hz, 2H), 1.80-1.71 (m, 1H), 1.49 (s, 3H);  13 C NMR (125 MHz, CDCl 3 ): δ 211.7, 136.4, 131.0, 127.1, 121.9, 119.8, 118.3, 111.0, 109.7, 72.2, 64.6, 64.5, 49.8, 49.3, 36.7, 36.6, 35.8, 22.7, 22.1. HRMS (m/z): [M+H] +  calcd. for C 19 H 23 N 2 O 2 , 311.1759, found 311.1755. 
     
       
         
         
             
             
         
       
     
     Methyl (2aR,6aR,8S,14bS)-2a-methoxy-5-oxo-1,2,2a,3,4,5,6,6a,8,9,14,14b-dodecahydroindolo[2′,3′:3,4]pyrido[1,2-a]quinoline-8-carboxylate (1r) 
     Off-white solid, 64 mg, 85% yield; mp: 114-116° C.; R f =0.4 (silica gel, hexane/EtOAc 1:2); [α] D =−92.8 (0.0018 M in acetone);  1 H NMR (500 MHz, Acetone) δ: 10.03 (s, 1H), 7.42 (d, J=7.7 Hz, 1H), 7.32 (t, J=10.0 Hz, 1H), 7.07 (t, J=6.0 Hz, 1H), 7.00 (t, J=6.0 Hz, 1H), 4.16-4.08 (m, 1H), 3.78 (s, 3H), 3.69 (dd, J=10.8, 3.8 Hz, 1H), 3.47 (dd, J=10.8, 5.0 Hz, 1H), 3.25 (s, 3H), 3.08-2.98 (m, 1H), 2.96-2.78 (m, 2H), 2.58-2.43 (m, 2H), 2.37-2.28 (m, 1H), 2.27-2.16 (m, 2H), 2.17-2.09 (m, 1H), 2.04-1.95 (m, 1H), 1.90-1.81 (m, 1H), 1.68-1.59 (m, 1H);  13 C NMR (125 MHz, Acetone): δ 208.6, 173.6, 137.6, 137.4, 135.4, 127.8, 121.7, 119.7, 118.4, 111.8, 106.2, 73.9, 62.7, 58.7, 52.2, 48.2, 38.1, 37.1, 30.6, 28.5, 26.6, 26.5; HRMS (m/z): [M+H] +  calcd. for C 22 H 27 N 2 O 4 , 383.1970, found 383.1981. 
     
       
         
         
             
             
         
       
     
     Methyl (2 aR, 6aR, 8R, 14b S)-2a-methoxy-5-oxo-1,2,2a, 3,4,5,6,6a, 8,9,14,14b-dodecahydroindolo[2′,3′:3,4]pyrido[1,2-a]quinoline-8-carboxylate (1s) 
     Off-white solid, 66 mg, 87% yield; mp: 113-16° C.; R f =0.4 (silica gel, hexane/EtOAc 1:2); [α] D =+95.2 (0.0005 M in acetone); NMR (500 MHz, Acetone): δ 9.99 (s, 1H), 7.43 (d, J=7.7 Hz, 1H), 7.32 (d, J=8.0 Hz, 1H), 7.06 (t, J=7.5 Hz, 1H), 7.00 (t, J=7.1 Hz, 1H), 4.17-4.07 (m, 1H), 3.79 (s, 3H), 3.69 (dd, J=10.6, 3.2 Hz, 1H), 3.47 (dd, J=10.6, 4.8 Hz, 1H), 3.25 (s, 3H), 3.07-2.99 (m, 1H), 2.94-2.88 (m, 1H), 2.85-2.80 (m, 1H), 2.59-2.43 (m, 2H), 2.38-2.27 (m, 1H), 2.27-2.18 (m, 2H), 2.17-2.09 (m, 1H), 2.05-1.96 (m, 1H), 1.90-1.80 (m, 1H), 1.68-1.60 (m, 1H);  13 C NMR (125 MHz, Acetone): δ 208.6, 173.6, 137.6, 135.4, 127.8, 121.7, 119.7, 118.4, 111.8, 106.2, 73.9, 62.7, 58.7, 52.3, 52.2, 48.2, 38.1, 37.1, 30.6, 28.5, 26.6, 26.5; HRMS (m/z): [M+H] +  calcd. for C 22 H 27 N 2 O 4 , 383.1970, found 383.1964. 
     Example 3 
     It describes the process for the preparation of compounds of general formula II, and the characterization data for the selected compounds of this class. 
     Compound of general formula I (0.1 mmol) was dissolved in THF:AcOH:water (0.4:0.4:0.4 mL) and NBS (0.1 mmol) was added slowly at −10° C. The reaction mixture was slowly warmed to room temperature and stirring continued for 2 h. After completion, the reaction mixture was quenched slowly with saturated sodiumbicarbonate solution at 0° C. Then, the reaction mixture was diluted with DCM (30 mL) and washed with water (2×20 mL). The organic layer was separated, dried over Na 2 SO 4  and concentrated under vacuum. The crude was purified on flash chromatography, using EtOAc in hexane as an eluent to obtain the title compounds of general formula II. 
     
       
         
         
             
             
         
       
     
     (3 S,3a′S,5a′R,9a′R)-5a′-methoxy-1′,2′,3a′,4′,5′,5a′,6′,7,′9′,9a′-decahydro-8′H-spiro[indoline-3,3′-pyrrolo[1,2-c)]quinoline]-2,8′-dione (it) 
     Off-white solid, 47% yield;  1 H NMR (500 MHz, CDCl 3 ) δ 8.74 (s, 1H), 7.24-7.15 (m, 2H), 7.08-6.98 (m, 1H), 6.90 (d, J=7.3 Hz, 1H), 3.49-3.40 (m, 1H), 3.30 (s, 3H), 3.04-2.93 (m, 1H), 2.69-2.58 (m, 1H), 2.54-2.28 (m, 6H), 2.23 (d, J=12.9 Hz, 1H), 2.02-1.89 (m, 2H), 1.82 (d, J=8.1 Hz, 1H), 1.68-1.57 (m, 1H), 1.46-1.35 (m, 1H). 1.35-1.29 (m, 1H);  13 C NMR (125 MHz, CDCl 3 ) δ 211.0, 181.3, 141.0, 134.0, 128.1, 123.1, 122.7, 109.7, 75.3, 73.7, 69.2, 56.1, 51.5, 49.0, 40.8, 36.6, 34.9, 31.9, 27.0, 22.2; LCMS (ESI): m/z 341 [M+H]±. 
     
       
         
         
             
             
         
       
     
     Methyl (1′S,3 S,3a′S,5a′R,9a′R)-5a′-methoxy-2,8′-dioxo-1′,2′,3a′,4′,5a′,6′,7′,8′,9′,9a′-decahydro-5H-spiro[indoline-3,3′-pyrrolo[1,2-d]quinoline]-1′-carboxylate (1u) 
     Off-white solid, 40% yield; NMR (500 MHz, CDCl 3 ) δ 7.77 (s, 1H), 7.37 (d, J=7.4 Hz, 1H), 7.22-7.17 (m, 1H), 7.07-7.01 (m, 1H), 6.84 (d, J=7.7 Hz, 1H), 4.21 (d, J=8.4 Hz, 1H), 3.57 (dd, J=11.4, 3.0 Hz, 1H), 3.32 (s, 3H), 3.18-3.14 (m, 1H), 2.97 (dd, J=14.8, 4.2 Hz, 1H), 2.77 (dd, J=13.9, 9.2 Hz, 1H), 2.68-2.59 (m, 1H), 2.52-2.43 (m, 1H), 2.39-2.33 (m, 1H), 2.28-2.20 (m, 1H), 2.14-2.07 (m, 1H), 1.96-1.90 (m, 1H), 1.82 (dd, J=13.9, 6.1 Hz, 1H), 1.59-1.51 (m, 1H), 1.49-1.41 (m, 1H), 1.33-1.27 (m, 1H);  13 C NMR (125 MHz, CDCl 3 ) δ 211.1, 180.6, 174.3, 140.6, 133.0, 128.3, 124.3, 123.1, 109.3, 73.8, 69.9, 64.0, 60.4, 56.1, 51.6, 49.1, 40.4, 39.4, 36.5, 31.3, 26.7, 22.4; LCMS (ESI): m/z 399 [M+H]±. 
     
       
         
         
             
             
         
       
     
     Methyl (1′R,3 S,3 8′,9′,9a′-decahydro-5H-spiro[indoline-3,3′-pyrrolo[1,2-d]quinoline]-1′-carboxylate (1v) 
     Off-white solid, 42% yield; NMR (500 MHz, CDCl 3 ) δ 7.79 (s, 1H), 7.40 (d, J=7.4 Hz, 1H), 7.22 (dd, J=7.6, 6.9 Hz, 1H), 7.07 (t, J=7.4 Hz, 1H), 6.86 (d, J=7.7 Hz, 1H), 4.23 (d, J=8.2 Hz, 1H), 3.78 (s, 3H), 3.59 (dd, J=11.4, 3.3 Hz, 1H), 3.34 (s, 3H), 3.20-3.16 (m, 1H), 3.00 (dd, J=14.8, 4.2 Hz, 1H), 2.79 (dd, J=13.9, 9.2 Hz, 1H), 2.70-2.62 (m, 1H), 2.54-2.46 (m, 1H), 2.42-2.35 (m, 1H), 2.30-2.22 (m, 1H), 2.15-2.10 (m, 1H), 1.95 (d, J=12.3 Hz, 1H), 1.84 (dd, J=13.8, 6.1 Hz, 1H), 1.61-1.53 (m, 1H), 1.52-1.42 (m, 1H), 1.35-1.29 (m, 1H);  13 C NMR (125 MHz, CDCl 3 ) δ 211.1, 180.6, 174.3, 140.6, 133.0, 128.3, 124.3, 123.1, 109.3, 73.8, 69.9, 64.0, 60.4, 56.1, 51.6, 49.1, 40.4, 39.4, 36.5, 31.3, 26.7, 22.4; LCMS (ESI): m/z 399 [M+H]±. 
     Example 4 
     It describes the process for the preparation of compounds of general formula VI, and the characterization data for the selected compounds of this class. 
     Compound of general formula V (0.1 mmol) was dissolved in THF:AcOH:water (0.4:0.4:0.4 mL) and NBS (0.1 mmol) was added slowly at −10° C. The reaction mixture was slowly warmed to room temperature and stirring continued for 2 h. After completion, the reaction mixture was quenched slowly with saturated sodiumbicarbonate solution at 0° C. Then, the reaction mixture was diluted with DCM (30 mL) and washed with water (2×20 mL). The organic layer was separated, dried over Na 2 SO 4  and concentrated under vacuum. The crude was purified on flash chromatography, using EtOAc in hexane as an eluent to obtain the title compounds of general formula VI. 
     
       
         
         
             
             
         
       
     
     (3S,3a′S,5a′R,9a′R)-5a′-Methoxy-1′,2′,3a′,4′,5′,5a′9′,9a′-octahydro-8′H-spiro[indoline-3,3′-pyrrolo[1,2-a]quinoline]-2,8′-dione (1w) 
     Off-white solid, 17 mg, 51% yield; mp: 213-215° C.; R f =0.4 (silica gel, hexane/EtOAc 1:4);  1 H NMR (500 MHz, Acetone-d 6 ): δ 9.35 (s, 1H), 7.39 (d, J=7.3 Hz, 1H), 7.18 (td, J=7.7, 1.1 Hz, 1H), 7.00 (t, J=7.5 Hz, 1H), 6.91 (d, J=7.7 Hz, 1H), 6.82 (d, J=10.3 Hz, 1H), 5.97 (d, J=10.3 Hz, 1H), 4.05-3.98 (m, 1H), 3.31 (s, 3H), 3.20-3.11 (m, 1H), 3.09-3.01 (m, 2H), 2.72 (d, J=8.8 Hz, 2H), 2.32-2.23 (m, 1H), 1.98-1.88 (m, 1H), 1.77-1.63 (m, 2H), 1.40-1.27 (m, 2H), 1.03-0.95 (m, 1H);  13 C NMR (125 MHz, Acetone-d 6 ): δ 198.8, 180.4, 156.7, 142.3, 134.5, 131.2, 128.3, 125.9, 122.4, 109.9, 75.4, 62.4, 57.1, 55.1, 50.7, 46.9, 35.4, 33.4, 30.4, 21.3; HRMS (m/z): [M+H] +  calcd. for C 20 H 23 N 2 O 3 , 339.1708, found 339.1715. 
     
       
         
         
             
             
         
       
     
     (3 S,3 aS,5aS,9aR)-5a-Methyl-1,2,3a,4,9,9a-hexahydrospiro[benzo[b]pyrrolo[1,2-d][1,4]oxazine-3,3′-indoline]-2′,8(5aH)-dione (1x) 
     Off-white solid, 17 mg, 52% yield; mp: 215-217° C.; R f =0.45 (silica gel, hexane/EtOAc 1:4);  1 H NMR (500 MHz, CD 3 OD): δ 7.31 (d, J=7.4 Hz, 1H), 7.22 (t, J=7.7 Hz, 1H), 7.07 (t, J=7.5 Hz, 1H), 6.87 (d, J=7.7 Hz, 1H), 6.67 (d, J=10.8 Hz, 1H), 6.03 (d, J=10.8 Hz, 1H), 3.70 (t, J=10.5 Hz, 1H), 3.49 (t, J=8.3 Hz, 1H), 3.28 (dd, J=10.5, 2.5 Hz, 1H), 2.88-2.80 (m, 2H), 2.77 (t, J=9.1 Hz, 1H), 2.69 (dd, J=10.1, 2.2 Hz, 1H), 2.49 (dd, J=17.4, 8.5 Hz, 1H), 2.28 (dt, J=13.0, 9.0 Hz, 1H), 2.07-2.01 (m, 1H), 1.43 (s, 3H) 13 C NMR (125 MHz, CD 3 OD): δ 199.2, 181.9, 155.6, 142.6, 134.4, 130.9, 129.4, 124.1, 123.8, 110.6, 74.4, 72.6, 69.7, 64.8, 55.7, 52.7, 41.3, 35.4, 24.9; HRMS (m/z): [M+H] +  calcd. for C 19 H 21 N 2 O 3 , 325.1552, found 325.1555. 
     
       
         
         
             
             
         
       
     
     Methyl (1′S, 3 S,3a′S,5a′R,9a′R)-5a′-methoxy-2,8′-dioxo-1′,2′,3a′,4′,5a′,8′,9′,9a′-octahydro-5H-spiro[indoline-3,3′-pyrrolo[1,2-d]quinoline]-1′-carboxylate (1y) 
     Off-white solid, 19 mg, 48% yield; mp: 246-248° C.; R f =0.4 (silica gel, hexane/EtOAc 1:4); [α] D =−12.5 (0.002 M in acetone);  1 H NMR (500 MHz, Acetone-d 6 ): δ 8.78 (s, 1H), 7.34 (d, J=7.3 Hz, 1H), 7.11 (td, J=7.7, 0.9 Hz, 1H), 6.95 (t, J=7.5 Hz, 1H), 6.80 (d, J=7.7 Hz, 1H), 6.52 (dd, J=10.2, 2.1 Hz, 1H), 6.08 (d, J=10.2 Hz, 1H), 4.07 (dd, J=9.0, 1.5 Hz, 1H), 3.74 (s, 3H), 3.44 (dd, J=10.1, 3.6 Hz, 1H), 3.27 (s, 3H), 3.20 (d, J=2.3 Hz, 1H), 3.03 (dd, J=16.4, 3.0 Hz, 1H), 2.56-2.49 (m, 1H), 2.12 (d, J=9.3 Hz, 1H), 1.46-1.25 (m, 3H);  13 C NMR (125 MHz, Acetone-d 6 ): δ 197.9, 179.8, 173.8, 148.0, 141.4, 132.5, 132.1, 128.0, 123.8, 122.3, 109.1, 71.5, 69.0, 62.0, 60.5, 55.6, 51.3, 50.5, 38.4, 37.9, 32.2, 21.5. HRMS (m/z): [M+H] +  calcd. for C 22 H 25 N 2 O 5 , 397.1763, found 397.1774. 
     Example 5 
     Study on Cellular and Mitochondrial Metabolic Functions 
     We examined the ability of compounds of the invention to enable the identification of chemotypes as potential inhibitors of mitochondrial functions. Such compounds would be useful not only as chemical probes targeting cellular energy metabolism but also as potential leads for the development of drugs targeting the mitochondrial function in cancer. Thus, the cellular mitochondrial activity was measured in Hepa1-6 cell line (CRL-1830, ATCC) after exposure to compounds of the invention for 24 h. These efforts identified compounds 1d and 1q as promising leads, which were found to deplete ATP production up to 60% and 50% ( FIG. 1 a   ), and reduce ΔΨm by 82% and 77%, respectively ( FIG. 1 b   ). The observed increase in redox potential ( FIG. 1 c   ), as a result of oxidative stress and accumulation of reducing equivalents, supports the idea of suppression and cellular stress response induction in Hepa1-6 cells due to the effect of compounds 1d and 1q. Additionally, the exposure of Hepa1-6 cells to 1d and 1q for 48 h resulted in a potent suppression of cells proliferation ( FIG. 1 d   ) without noticeable cytotoxic necrosis ( FIG. 1 e   ). Furthermore, compounds 1d and 1q were shown to diminish the proliferation of Hepa1-6 to different degrees with compound 1d being the most potent. 
     Since ATP is the main product of the mitochondria as the cells powerhouse, the decrease in ATP content indicated the ability of compounds 1d and 1q to interfere with the machinery of cellular energy metabolism. This was validated by a parallel inhibition of the ΔΨm with the maximum response observed at a concentration of 1 μM decreasing the normalized ΔΨm in the test system by 90% (1q), 82% (1d) ( FIG. 1 b   ). In addition, 1d and 1q strongly affected the redox potential to a point where the cells succumb to the induced stress ( FIG. 1 c   ). The inhibition of glycolysis and the consequent downregulation of ATP are utilized not only for targeting cancer cells but also to sensitize the resistant cancer cells to classical chemotherapies such as, doxorubicin, cisplatin and paclitaxel. 
     Example 6 
     Induced Proliferation Study 
     After seeing the ability of compounds 1d and 1q to target mitochondrial machinery, we tested their effect on T- and B-cells activation and proliferation. Interestingly, compounds 1d and 1q did not suppress T- and B-cell function as indicated by the non-significant effects on the division indices ( FIGS. 2 a , 2 c   ) or expansion indices ( FIGS. 2 b , 2 d   ) of T- and B-cells upon stimulation using phorbol 12-myristate 13-acetate (PMA) (PMA)/Ionomycin. In addition, treatment of isolated T-cells with 1d and 1q did not significantly affect the activation-induced proliferation upon stimulation of T-cells with either anti-CD3/CD28 antibodies or cytokines IL-2/IL-7 ( FIGS. 2 e , 2 f   ). Thus, while retaining the suppressive effect on the proliferation of the highly metabolically active Hepa1-6, these compounds did not suppress T- and B-cell activation. Thus, the overall impact of 1d and 1q on metabolism appears to be a driving force in the inhibition of cell proliferation. This inhibition of mitochondrial functions in cancer cells without altering the immunologic al activation or reprogramming of T- and B-cells, represents a promising strategy in cancer immunotherapy. 
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