shown below are exemplary carbazole compounds , compounds 1 - 8 , of this invention . the carbazole compounds described above can be prepared by methods well known in the art , as well as by the synthetic routes disclosed herein . for example , one can react 3 , 6 - dibromocarbazole with an olefin containing a heteroaryl group with at least one nitrogen atom in the presence of a palladium catalyst to produce an intermediate , 3 , 6 - bis ( heteroaryl - vinyl )- carbazole . the intermediate can then be treated with methyl iodide to produce a corresponding iodide salt . as another example , one can react 3 , 6 - diaminocarbazole with a formaldehyde containing a heteroaryl group with at least one nitrogen atom to produce an intermediate , 3 , 6 - bis ( heteroaryl - methylidene - imino )- carbazole . similarly , this intermediate can also be converted to a corresponding iodide salt upon treating with methyl iodide . shown below is a scheme that depicts the synthesis of compounds 1 - 8 mentioned above . details of synthesis of compounds 1 - 8 are described in examples 1 - 8 , respectively . to prepare other carbazole compounds , pyridinyl or pyrazinyl shown in the above scheme can be replaced by another heteroaryl containing at least one nitrogen atom ( e . g ., pyrrolyl , imidazolyl , pyrimidinyl , or indolyl ). the chemicals used in the above - described synthetic route may include , for example , solvents , reagents , catalysts , protecting group reagents , and deprotecting group reagents . the methods described above may additionally include steps , either before or after the steps described specifically herein , to add or remove suitable protecting groups in order to ultimately allow synthesis of a carbazole compound . in addition , various synthetic steps may be performed in an alternate sequence or order to give the desired carbazole compounds . synthetic chemistry transformations and protecting group methodologies ( protection and deprotection ) useful in synthesizing applicable carbazole compounds are known in the art and include , for example , those described in r . larock , comprehensive organic transformations , vch publishers ( 1989 ); t . w . greene and p . g . m . wuts , protective groups in organic synthesis , 2d . ed ., john wiley and sons ( 1991 ); l . fieser and m . fieser , fieser and fieser &# 39 ; s reagents for organic synthesis , john wiley and sons ( 1994 ); and l . paquette , ed ., encyclopedia of reagents for organic synthesis , john wiley and sons ( 1995 ) and subsequent editions thereof . a carbazole compound thus synthesized can be further purified by a method such as column chromatography , high - pressure liquid chromatography , or recrystallization . note that the carbazole compounds contain at least two double bonds , and may further contain one or more asymmetric centers . thus , they can occur as racemates and racemic mixtures , single enantiomers , individual diastereomers , diastereomeric mixtures , and cis - or trans - or e - or z - double bond isomeric forms . all such isomeric forms are contemplated . also within the scope of this invention is a pharmaceutical composition contains an effective amount of at least one carbazole compound described above and a pharmaceutical acceptable carrier . further , this invention covers a method for stabilizing a g - quadruplex of a human telomere or a telomere of other mammals . this method can be used to treat a subject with telomerase - related diseases ( e . g ., cancer ) by administering to it an effective amount of one or more of carbazole compounds . such a subject can be identified by a health care professional based on results from any suitable diagnostic method . this invention also covers a method for detecting cancer cells in a subject by contacting cells with a certain concentration of a carbazole compound described above and calculating the percentage of the cells that emit florescence upon irradiation with an excitation light . if the percentage is above a pre - set value ( e . g ., 30 %), the subject is determined to contain cancer cells . the pre - set value can be determined empirically and can vary depending upon the concentration and the type of the carbazole compound used and the type of the cells targeted . for example , the pre - set value can be determined by respectively contacting cancer cells and normal cells with one of the carbazole above - described compounds and subsequently calculating the percentages of the cancer cells and normal cells that emit fluorescence upon irradiation of an excitation light . the pre - set value can then be selected statistically such that it is greater than the percentage of the normal cells that emit fluorescence , but the same as or lower than the percentage of the cancer cells that emit fluorescence . when using the method of this invention to treat a subject with telomerase - related disease , one can determine effective doses by methods well known in the art . for example , the interrelationship of dosages for animals and humans ( based on milligrams per meter squared of body surface ) is described in freireich et al ., ( 1966 ) cancer chemother rep 50 : 219 . body surface area may be approximately determined from height and weight of the patient . see , e . g ., scientific tables , geigy pharmaceuticals , ardley , n . y ., 1970 , 537 . an effective amount of the carbazole compounds can range from about 0 . 1 mg / kg to about 100 mg / kg . effective doses will vary , as recognized by those skilled in the art , depending on , e . g ., the types of diseases treated , route of administration , excipient usage , and the possibility of co - usage with other therapeutic treatment . to treat a telomerase - related disease , a composition having one or more of the above - mentioned compounds can be administered parenterally , orally , nasally , rectally , topically , or buccally . the term “ parenteral ” as used herein refers to subcutaneous , intracutaneous , intravenous , intramuscular , intraarticular , intraarterial , intrasynovial , intrasternal , intrathecal , intralesional , intraperitoneal , intratracheal or intracranial injection , as well as any suitable infusion technique . a sterile injectable composition can be a solution or suspension in a non - toxic parenterally acceptable diluent or solvent , such as a solution in 1 , 3 - butanediol . among the acceptable vehicles and solvents that can be employed are mannitol , water , ringer &# 39 ; s solution , and isotonic sodium chloride solution . in addition , fixed oils are conventionally employed as a solvent or suspending medium ( e . g ., synthetic mono - or diglycerides ). fatty acid , such as oleic acid and its glyceride derivatives are useful in the preparation of injectables , as are natural pharmaceutically acceptable oils , such as olive oil or castor oil , especially in their polyoxyethylated versions . these oil solutions or suspensions can also contain a long chain alcohol diluent or dispersant , or carboxymethyl cellulose or similar dispersing agents . other commonly used surfactants such as tweens or spans or other similar emulsifying agents or bioavailability enhancers which are commonly used in the manufacture of pharmaceutically acceptable solid , liquid , or other dosage forms can also be used for the purpose of formulation . a composition for oral administration can be any orally acceptable dosage form including capsules , tablets , emulsions , and aqueous suspensions , dispersions , and solutions . in the case of tablets , commonly used carriers include lactose and corn starch . lubricating agents , such as magnesium stearate , are also typically added . for oral administration in a capsule form , useful diluents include lactose and dried corn starch . when aqueous suspensions or emulsions are administered orally , the active ingredient can be suspended or dissolved in an oily phase combined with emulsifying or suspending agents . if desired , certain sweetening , flavoring , or coloring agents can be added . a nasal aerosol or inhalation composition can be prepared according to techniques well known in the art of pharmaceutical formulation . for example , such a composition can be prepared as a solution in saline , employing benzyl alcohol or other suitable preservatives , absorption promoters to enhance bioavailability , fluorocarbons , and / or other solubilizing or dispersing agents known in the art . a composition having one or more active above - described compounds can also be administered in the form of suppositories for rectal administration . a pharmaceutically acceptable carrier is routinely used with one or more active above - mentioned compounds . the carrier in the pharmaceutical composition must be “ acceptable ” in the sense that it is compatible with the active ingredient of the composition ( and preferably , capable of stabilizing the active ingredient ) and not deleterious to the subject to be treated . one or more solubilizing agents can be utilized as pharmaceutical excipients for delivery of an above - mentioned compound . examples of other carriers include colloidal silicon oxide , magnesium stearate , cellulose , sodium lauryl sulfate , and d & amp ; c yellow # 10 . the carbazole compounds of this invention can be preliminarily screened for their efficacy in stabilizing g - quadruplexes by in vitro assays ( see example 9 below ). other methods will also be apparent to those of ordinary skill in the art . the specific examples below are to be construed as merely illustrative , and not limitative of the remainder of the disclosure in any way whatsoever . without further elaboration , it is believed that one skilled in the art can , based on the description herein , utilize the present invention to its fullest extent . all publications cited herein are hereby incorporated by reference in their entirety . 3 , 6 - dibromocarbazole ( 1 . 63 g , 5 mmol , aldrich ) was added into a high pressure flask containing a mixture of palladium ( ii ) acetate ( 15 mg , strem ) and tri - o - tolyl phosphine ( 150 mg , aldrich ). to this flask was added a mixed solvent ( triethylamine 5 ml / acetonitrile 15 ml ) and 4 - vinylpyridine ( 2 g , 20 mmol , merck ). the flask was sealed after bubbling nitrogen for 10 minutes . after keeping the reaction at ˜ 105 ° c . for three days , precipitate was collected and then washed with h 2 o / ch 2 cl 2 twice . the resultant insoluble solid was filtered and dissolved in thf , then dried over anhydrous mgso 4 . compound 1 was collected as a yellow powder by filtration after recrystallization from thf filtrate ( yield : 62 %, mp & gt ; 300 ° c .). 1 h nmr ( cd 3 od ): δ 8 . 42 ( d , j = 5 . 7 hz , 4h ), 8 . 25 ( s , 2h ), 7 . 65 ( d , j = 8 . 4 hz , 2h ), 7 . 56 ( d , j = 16 . 2 hz , 2h ), 7 . 45 ( d , j = 5 . 7 hz , 4h ), 7 . 42 ( d , j = 8 . 4 hz , 2h ), 7 . 07 ( d , j = 16 . 2 hz , 2h ). ea ( 373 + 1 . 5h 2 o ): calc ( obs %) c : 83 . 64 ( 78 . 20 ), h : 5 . 09 ( 5 . 14 ), n : 11 . 26 ( 10 . 38 ). after refluxing 3 , 6 - di ( 4 - vinylpyridine ) carbazole obtained in example 1 with excess ch 3 i in acetone , compound 2 was collected as an orange - red powder by filtration after recrystallization from methanol twice ( yield : 92 %, mp & gt ; 300 ° c .). 1 h nmr ( dmso - d6 ): δ 8 . 77 ( d , j = 6 . 9 hz , 4h ), 8 . 59 ( s , 2h ), 8 . 19 ( d , j = 6 . 9 hz , 4h ), 8 . 20 ( d , j = 15 . 9 hz , 2h ), 7 . 90 ( d , j = 8 . 7 hz , 2h ), 7 . 64 ( d , j = 8 . 7 hz , 2h ), 7 . 53 ( d , j = 15 . 9 hz , 2h ). ea ( 657 + 1 . 0h 2 o ): calc ( obs %) c : 51 . 14 ( 49 . 87 ), h : 3 . 81 ( 4 . 03 ), n : 6 . 39 ( 6 . 32 ). compound 3 was prepared in a manner similar to that described in example 1 . compound 4 was prepared in a manner similar to that described in example 2 . compound 5 was prepared in a manner similar to that described in example 1 . compound 6 was prepared in a manner similar to that described in example 2 . compound 7 was prepared in a manner similar to that described in example 1 . compound 8 was prepared in a manner similar to that described in example 2 . calf thymus ( ct - dna ) and oligonucleotides at , ld , gc , g10 , lq1 , lq2 , lq4 , tet12 , apt , oxy12 , oxy28 , hum12 , and hum24 were purchased from applied biosystems . the sequences of these oligonucleotides are listed below : at : 5 ′-( at ) 6 - 3 ′ ( seq id no : 1 ) ld : 5 ′- gcgca2t2gcgc - 3 ′ ( seq id no : 2 ) gc : 5 ′-( gc ) 6 - 3 ′ ( seq id no : 3 ) g10 : 5 ′- d ( g ) 10 - 3 ′ ( seq id no : 4 ) lq1 : 5 ′- tg 4 t - 3 ′ ( seq id no : 5 ) lq2 : 5 ′- t 2 g 4 t 2 - 3 ′ ( seq id no : 6 ) lq4 : 5 ′- t 4 g 4 - 3 ′ ( seq id no : 7 ) tet12 : 5 ′-( t 2 g 4 ) 2 - 3 ′ ( seq id no : 8 ) apt : 5 ′- g 2 t 2 g 2 tgtg 2 t 2 g 2 - 3 ′ ( seq id no : 9 ) oxy12 : 5 ′- g 4 t 4 g 4 - 3 ′ ( seq id no : 10 ) 0xy28 : 5 ′- g 4 ( t 4 g 4 ) 3 - 3 ′ ( seq id no : 11 ) hum12 : 5 ′-( t 2 ag 3 ) 2 - 3 ′ ( seq id no : 12 ) hum24 : 5 ′-( t 2 ag 3 ) 4 - 3 ′ ( seq id no : 13 ) among them , ct - dna and oligonucleotides at , ld , and gc , can form duplexes , while oligonucleotides g10 , lq1 , lq2 , lq4 , tet12 , apt , oxy12 , oxy28 , hum12 , and hum24 can form quadruplexes . for example , apt can form a very stable unimolecular quadruplex with two g - quartets connected by one lateral tgt loop at one end and two parallel tt loops at the other end . hum24 can form a unimolecular quadruplex with one diagonal t 2 a - loop at one end and two parallel t 2 a - loops at the other end of g - quartets . tet12 and hum12 can form a dimeric hairpin quadruplex with lateral loops . oxy12 can form a dimeric hairpin quadruplex with a diagonal loop at each end of the quartets . carbazole compounds and their complexes with dna duplexes and quadruplexes were studied by absorption spectroscopy , fluorescence spectroscopy , and circular dihcroism ( cd ): each oligonucleotide described above was mixed with a solution of 10 mm tris - hcl ( ph 7 . 5 ) and 150 mm nacl and was denatured at 90 ° c . for 2 min . the mixture was then cooled slowly to room temperature and stored at 4 ° c . for more than 2 days before use . a test compound was then added to this solution to form a compound / dna complex . the resultant complex was subjected to absorption analysis using a hitachi u3200 uv - visible spectrophotometer . the absorption spectra were taken for compound 2 and its complex with each oligonucleotide . the results showed that the absorption peak of compound 2 red shifted from ˜ 435 nm to ˜ 450 nm in the presence of a dna duplex and further to ˜ 460 nm in the presence of a dna quadruplex . in addition , the molar absorption coefficient decreased by ˜ 15 % in the presence of a dna duplex and ˜ 35 % in the . presence of a dna quadruplex . these spectra changes indicate that compound 2 binds to duplexes and quadruplexes . compound 2 was mixed with eleven dnas and subjected to fluorescence analysis at λ ex ≈ 430 nm , using a hitachi f4010 spectrofluorimeter with a 2 nm bandwidth in a 1 - cm cell . fluorescence analysis was also carried out for compound 4 or 6 in the presence of hum24 . the results showed that the fluorescence of each of compounds 2 , 4 , and 6 was weak . however , the fluorescence intensity unexpectedly increased in an order of magnitude in the presence of a dna duplex and in two orders of magnitude in the presence of a dna quadruplex . further , the fluorescence peaks for a complex of compound 2 and a dna duplex and a complex of compound 2 and a dna quadruplex were at ˜ 550 nm and ˜ 575 nm , respectively . these results suggest that compounds 2 , 4 , and 6 can be used to distinguish dna duplexes from dna quadruplexes . in addition , these compounds possess enhanced fluorescence upon binding to dna quadruplexes and , therefore , can be used as a biomarker for dna quadruplexes in electrophoresis . eight dna quadruplexes and their complexes with compound 2 were subjected to cd analysis . cd spectra were averaged 10 scans on a jasco j - 715 spectropolarimeter with a 2 nm bandwidth . the scan speed was 50 nm / min and the step resolution was 0 . 2 nm . no appreciable changes were detected in the cd spectra of dna quadruplexes before and after compound 2 bound to them , suggesting that they were not distorted by binding with compound 2 . the cd spectra also confirmed that anti - parallel quadruplexes dominate in hum 12 , hum24 , oxy12 , oxy28 , tet12 , and apt . further , hum24 and its complexes with compounds 2 , 4 , 6 , and 8 were subjected to temperature - dependent cd analysis . the results showed that the melting temperature of hum24 quadruplex increased in the presence of each of the four test compounds , indicating improved thermal stability . compound 2 and its complexes with dna quadruplexes were further studied by polyacrylamide gel eletrophoresis ( page ). more specifically , compound 2 / dna quadruplexes described above were analyzed by page in 20 % native gels in 10 mm tris - hcl and 150 mm nacl ( ph 7 . 5 ). gel electrophoresis was carried out in an electric field of 100 v / cm at 4 ° c . for 15 hours . dna concentrations were determined by absorbencies at 260 nm and were adjusted to about 10 μm per unit structure . after photographing with uv shadowing , gels were post - stained in a solution containing 10 μm of compound 2 , 10 mm tris - hcl , and 150 mm nacl ( ph 7 . 5 ) at room temperature for 10 seconds . the gels were then rinsed by distilled water and photographed under 254 nm uv light using a digital camera . gels were post - stained with compound 2 after electrophoresis of at , ld , gc , g10 , lq1 , lq2 , lq4 , tet12 , oxy12 , hum12 , apt , oxy28 , and hum24 was complete . the results showed that that most dnas exhibited fluorescence bands under 254 nm uv light . in particular , most dnas migrated in the gel in a single band , but tet12 and lq4 migrated in two bands . pre - stained gels were used for selectivity assays . a 0 . 1 μm compound 2 solution was initially incubated with 10 μm of different dna solutions for 10 minutes . gel electrophoresis was then carried out in an electric field of 100 v / cm at 4 ° c . for 6 hours . all of the pre - stained gels were photographed under 254 nm uv light using a bio - rad imaging detector . gels pre - stained with compound 2 were used before running electrophoresis for at , ld , gc , g10 , lq1 , lq2 , lq4 , tet12 , oxy12 , hum12 , apt , oxy28 , and hum24 . the results showed that the complexes of compound 2 and the quadruplexes of lq2 , lq4 , oxy12 , oxy28 , and hum24 exhibited fluorescence bands under 254 nm uv light . further , the complex of compound 2 and tet12 quadruplex only exhibited a third fluorescence band in pre - stained gel electrophoresis , which was different from the two bands observed in post - stained gel electrophoresis . this third band is ascribed to be a linear tetramer of tet12 . on the other hand , no fluorescence bands were detected in the complexes of compound 2 and the quadruplexes of ld , at , gc , g10 , lq1 , hum12 , and apt . as mentioned above , hum24 , oxy12 , and oxy28 contain at least one diagonal loop in their anti - parallel quadruplexes , and apt , tet12 , and hum12 contain no diagonal loop in their anti - parallel quadruplexes . upon binding to compound 2 , hum24 , oxy12 , and oxy28 exhibited fluorescence bands , while apt , tet12 , and hum12 exhibited no fluorescence bands resulted from anti - parallel quadruplexes . this observation suggests that compound 2 can distinguish anti - parallel quadruplexes with diagonal loops from anti - parallel quadruplexes without diagonal loops . in addition , fluorescence was exhibited by the complexes of compound 2 and the linear tetramers of lq2 ( containing t 2 tails ) and lq4 ( containing t 4 tails ), but not by those of compound 2 and the linear tetramers of lq1 ( containing t tails ) and g10 ( containing no t tails ). these results suggest that compound 2 can also distinguish linear tetramers with different lengths of t tails . to study the sensitivity of dna detection using electrophoresis described above , a solution containing 0 . 1 μm of compound 2 was incubated with solutions containing 2 . 5 to 0 . 005 μm of hum24 . the mixtures were then subjected to electrophoresis . the sensitivity assay shows that 0 . 1 μm of a compound 2 solution can detect the presence of 0 . 01 μm of hum24 quadruplex , indicating that compound 2 is a sensitive biomarker for detecting the presence of hum24 . furthermore , the results also show that 0 . 1 μm of a compound 2 solution can detect the presence of 0 . 1 μm of lq4 quadruplex , 0 . 1 μm of oxy28 quadruplex , and a small amount of linear tetramer in 0 . 25 μm of tet12 quadruplex . a wide - field fluorescence microscopy was custom made for diagnosing cancer cells . the microscopy consists of an ar + laser ( coherent inc . santa clara , calif .) as the light source , a sensitive cooled charged - coupled device ( ccd ) camera ( dv465 - uv , andor technology , south windsor , conn .) for imaging , and two avalanche photodiodes ( apds ) for transient photoluminescence measurement . excitation and imaging were conducted by an oil immersion microscope objective with a numerical aperture of 1 . 3 . a dichroism mirror ( omega ) was used to direct the fluorescence into the ccd camera . a holographic notch filter ( oriel ) was used to block the backscattered laser light . images of 250 × 250 pixels were recorded at a high speed . the imaged area was 50 × 50 μm 2 and the spatial resolution was about 2 pixels . the following cells were tested : cl1 - 1 human lung cancer cells , h1299 lung cancer cells , htert - bj lung cancer cells , ca9 - 22 oral cancer cells , hela cervical cancer cells , kj - 1 nasopharyngeal cancer cells , hacat keratinocyte cells , detroit - 551 skin normal cells , imr - 90 lung normal cells , and bj - 1 lung fibroblast cells . specifically , cells were incubated with 0 . 1 μm of compound 2 in a culture medium for 3 - 6 hours . the non - fixed cells were washed three times with phosphate - buffered saline and then studied under the wide - field fluorescence microscope . unexpectedly , for each type of tested cancer cells , more than 70 % of the cells exhibited bright fluorescence . by contrast , for each type of tested normal cells , only less than 20 % of the cells exhibited bright fluorescence . kj - 1 nasopharyngeal carcinoma cancer cells were treated with 0 . 1 μm of compound 2 , 0 . 1 μm of c15 ( i . e ., 9 -( 4 -( n - methyl - piperidinium )- butyl )- 3 , 6 - bis -( 1 - methyl - 4 - vinylpyridium ) carbazole iodine ), or an identical volume of dmso ( drug vehicle control ). the cells were incubated in t25 tissue culture flasks at 300 , 000 / flask for 3 or 4 days , then trypsinized and counted . 300 , 000 cells were then removed from the culture flask and reseeded onto a new culture flask with another 0 . 1 μm of compound 2 , 0 . 1 μm of c15 , or an identical volume of dmso . this procedure was repeated until when there were less than 300 , 000 cells available for reseeding . test results were obtained from at least 3 independent experiments . the results show that the kj - 1 cancer cells stopped proliferating after the treatment with compound 2 on day 10 . unexpectedly , cell proliferation was not affected by the treatment of c15 even on day 50 . the c15 - treated cells grew and repopulated at the same rate as the control cells . all of the features disclosed in this specification may be combined in any combination . each feature disclosed in this specification may be replaced by an alternative feature serving the same , equivalent , or similar purpose . thus , unless expressly stated otherwise , each feature disclosed is only an example of a generic series of equivalent or similar features . from the above description , one skilled in the art can easily ascertain the essential characteristics of the present invention , and without departing from the spirit and scope thereof , can make various changes and modifications of the invention to adapt it to various usages and conditions . thus , other embodiments are also within the scope of the following claims .