ASYMMETRIC BENZOXANTHENE DYES

Abstract: A class of asymmetric monobenzoxanthene compounds useful as fluorescent dyes are disclosed having structure (I) wherein Y1 and Y2 are individually hydroxyl, amino, imminium, or oxygen, R1-R8 are hydrogen, fluorine, chlorine, alkyl, alkene, alkyne, sulfonate, amino, amido, nitrile, alkoxy, linking group, and combinations thereof, and R9 is acetylene, alkane, alkene, cyano, substituted phenyl, and combinations thereof. The invention further includes novel intermediate compounds useful for the synthesis of asymmetric benzoxanthene compounds having general structure (II) where substituents R3-R7 correspond to like-referenced substituents in the structure of described above, and Y2 is hydroxyl or amine. In another aspect, the invention includes methods for synthesizing the above dye compounds and intermediates. In yet another aspect, the present invention includes reagents labeled with the asymmetric benzoxanthene dye compounds, including deoxynucleotides, dideoxynucleotides, phosphoramidites, and polynucleotides. In an additional aspect, the invention includes methods utilizing such dye compounds and reagents including dideoxy polynucleotide sequencing and fragment analysis methods.

Description: ASYMMETRIC BENZOXANTHENE DYES FIELD OF THE INVENTION This invention relates generally to fluorescent dye compounds useful as molecular probes. More specifically, this invention relates to asymmetric benzoxanthene dyes useful as fluorescent labeling reagents. BACKGROUND The non-radioactive detection of biological analytes is an important technology in modern analytical biotechnology. By eliminating the need for radioactive labels, safety is enhanced and the environmental impact of reagent disposal is greatly reduced, resulting in decreased costs for analysis. Examples of methods utilizing such non-radioactive detection methods include DNA sequencing, oligonucleotide probe methods, detection of polymerase- chain-reaction products, immunoassays, and the like. In many applications the independent detection of multiple spatially overiapping analytes in a mixture is required, e.g., single-tube multiplex DNA probe assays, immuno assays, multicolor DNA sequencing methods, and the like. In the case of multi-loci DNA probe assays, by providing multicolor detection, the number of reaction tubes may be reduced thereby simplifying the experimental protocols and facilitating the manufactiiring of application-specific kits. In the case of automated DNA sequencing, multicolor labeling allows for the analysis of all four bases in a single lane thereby increasing throughput over single-color methods and eliminating uncertainties associated with inter-lane electrophoretic mobility variations. Multiplex detection imposes a number of severe constraints on the selection of dye labels, particularly for analyses requiring an electrophoretic separation and treatment with enzymes, e.g., DNA sequencing. First, it is difficult to find a collection of dyes whose emission spectra are spectrally resolved, since the typical emission band half-width for organic fluorescent dyes is about 40-80 nanometers (nm) and the width of the available spectrum is limited by the excitation light source. As used herein the term "spectral resolution" in reference to a set of dyes means that the fluorescent emission bands of the dyes are sufficiently distinct, i.e., sufficiently non-overlapping, that reagents to which the respective dyes are attached, e.g. polynucleotides, can be distinguished on the basis of the fluorescent signal generated by the respective dyes using standard photodetection systems, e.g. employing a system of band pass filters and photomultiplier tubes, charged-coupled devices and spectrographs, or the like, as exemplified by the systems described in U.S. Pat. Nos. 4,230,558, 4,811,218, or in Wheeless et al, pgs. 21-76, in Flow Cytometry: Instrumentation and Data Analysis (Academic Press, New York, 1985). Second, even if dyes with non-overlapping emission spectra are found, the set may still not be suitable if the respective fluorescent efficiencies are too low. For example , in the case of DNA sequencing, increased sample loading can not compensate for low fluorescence efficiencies, Pringie et al., DNA Core Facilities Newsletter, 1: 15-21 (1988). Third, when several fluorescent dyes are used concurrently, simultaneous excitation becomes difficult because the absoφtion bands of the dyes are widely separated. Fourth, the charge, molecular size, and conformation of the dyes must not adversely affect the electrophoretic mobilities of the fragments. Finally, the fluorescent dyes must be compatible with the chemistry used to create or manipulate the fragments, e.g., DNA synthesis solvents and reagents, buffers, polymerase enzymes, ligase enzymes, and the like. Because of these severe constraints only a few sets of fluorescent dyes have been found that can be used in multicolor applications, particularly in the area of four-color DNA sequencing, e.g., Smith et al., Nucleic Acids Research, 113; 2399-2412 (1985); Prober et al., Science, 238: 336-341 (1987); and Connell et al., Biotechmques, 5: 342-348 (1987). FIG. 1 shows examples of fluorescent xanthene dyes currently used as long-wavelength labels emitting above 550 nm including the two rhodamine-based dyes TAMRA (22) and ROX (26) and the two fluorescein-based dyes HEX (23) and NAN (24). SUMMARY The present invention is directed towards our discovery of a class of asymmetric benzoxanthene dyes useful as fluorescent dyes. It is an object of our invention to provide a class of asymmetric benzoxanthene dyes useful for the simultaneous detection of multiple spatially-overlapping analytes which satisfies the constraints described above and provide fluorescence emission maxima above 550 nm when illuminated by excitation light having a wavelength of between 480 nm and 550 nm. It is a further object of our invention to provide a class of asymmetric benzoxanthene dyes useful for the simultaneous detection of multiple spatially-overlapping analytes which satisfies the constraints described above and whose fluorescence properties may be tuned by manipulation of substituents at a variety of positions. It is another object of our invention to provide methods and intermediate compounds useful for the synthesis of the asymmetric benzoxanthene dyes of our invention. It is a further object of our invention to provide nucleotides and polynucleotides labeled with the asymmetric benzoxanthene dyes of our invention. It is another object of our invention to provide phosphoramidite compounds including the asymmetric benzoxanthene dyes of our invention. It is another object of our invention to provide fragment analysis methods, including DNA sequencing methods, employing the asymmetric benzoxanthene dyes of our invention. In a first aspect, the foregoing and other objects of our invention are achieved by an asymmetric benzoxanthene dye compound having the formula: wherein Yi and Y 2 taken separately are hydroxyl, oxygen, i minhim, or amine. Ri-Rg taken separately are hydrogen, fluorine, chlorine, lower alkyl, lower alkene, lower alkyne, sulfonate, amino, ammonium, amido, nhrile, alkoxy, linking group, or combinations thereof. And, Ro is acetylene, alkane, alkene, cyano, substituted phenyl, or combinations thereof, the substituted phenyl having the structure: wherein Xi is carboxyiic acid or sulfonic acid; X 2 and Xs taken separately are hydrogen, chlorine, fluorine, or lower alkyl; and X 3 and X» taken separately are hydrogen, chlorine, fluorine, lower alkyl, carboxyiic acid, sulfonic acid, or linking group. In a second aspect, the invention includes phosphoramidite compounds having the formula: wherein X is a spacer arm; Y is a linkage; Bi is a phosphite ester protecting group; B 2 , and B 3 taken separately are selected from the group consisting of lower alkyl, lower alkene, lower aryl having between 1 and 8 carbon atoms, arylalkyl, and cycloalkyl containing up to 10 carbon atoms; and D is the asymmetric benzoxanthene dye compound described above. Y and D are linked through a linkage formed by the reaction of a linking group and its complementary functionality, such linkage being attached to dye D at one of positions Ri-Ro . In a third aspect, the invention includes a phosphoramidite compound having the formula: wherein Bi is a phosphite ester protecting group, B 2 and B 3 taken separately are selected from the group consisting of lower alkyl, lower alkene, lower aryl having between 1 and 8 carbon atoms, arylalkyl and cycloalkyl containing up to 10 carbon atoms; B 5 is an aάd-cleavable hydroxyl protecting group; B is a nucleotide base; and D is the dye compound described above. When B is purine or 7-deazapurine, the sugar moiety is attached at the ^-position of the purine or 7-deazapurine, and when B is pyrimidine, the sugar moiety is attached at the N'-posrtion of the pyrimidine. B and D are linked through a linkage formed by the reaction of a linking group and its complementary functionality, such linkage being attached to D at one of positions Ri-Ro . If B is a purine, the linkage is attached to the 8-position of the purine, if B is 7-deazapurine, the linkage is attached to the 7-position of the 7-deazapurine, and if B is pyrimidine, the linkage is attached to the 5-position of the pyrimidine. Preferably B is selected from the group consisting of uracil, cytosine, 7-deazaadenine, and 7-deazaguanosine. In a fourth aspect, the present invention includes a compound useful as an intermediate in the synthesis of the above described asymmetric benzoxanthene dyes, such compound having the formula: wherein R 3 -R 7 are as described above and Y is hydroxyl or amine. In a particulariy preferred embodiment of this aspect, R 3 is fluorine and Y 2 is hydroxyl. In a fifth aspect, the invention includes a nucleotide labeled with the above described asymmetric benzoxanthene dyes of the invention, the nucleotide having the formula: wherein B is a 7-deazapurine, purine, or pyrimidine nucleotide base; Wi and W 2 taken separately are H or OH; W 3 is OH, and, D is a dye compound of the invention. When B is purine or 7-deazapurine, the sugar moiety is attached at the N 9 -position of the purine or deazapurine, and when B is pyrimidine, the sugar moiety is attached at the N'-position of the pyrimidine. The linkage linking B and D is attached to D at one of positions R 1 -R 9 . If B is a purine, the linkage is attached to the 8-position of the purine, if B is 7-deazapurine, the linkage is attached to the 7-position of the 7-deazapurine, and if B is pyrimidine, the linkage is attached to the 5-position of the pyrimidine. Preferably B is selected from the group consisting of uracil, cytosine, deazaadenine, and deazaguanosine. In a sixth aspect, the invention includes labeled polynucleotides containing a nucleotide having the formula: wherein B is a 7-deazapurine, purine, or pyrimidine nucleotide base; Zi is H or OH; Z 2 is H, OH, HPO^ and Nuc, wherein "Nuc" refers to a nucleotide. The nucleoside and Nuc are linked by a phosphodiester linkage, the linkage being attached to the 5' -position of Nuc; Z 3 is selected from the group consisting of H, HPO 3 and phosphate analogs thereof, and Nuc, wherein Nuc and the nucleoside are linked by a phosphodiester linkage, the linkage being attached to the 3 '-position of Nuc; and D is a dye compound of the inventioa Phosphate analogs of HPO3 include analogs wherein a non-bridging oxygen is replaced by a non-oxygen moiety, e.g., sulphur, amino, anilidate, anilinthioate, and the like. When B is purine or 7-deazapurine, the sugar moiety is attached at the N 9 -position of the purine or deazapurine, and when B is pyrimidine, the sugar moiety is attached at the N'-posraon of the pyrimidine. The linkage linking B and D is attached to D at one of positions R1-R . If B is a purine, the linkage is attached to the 8-position of the purine, if B is 7-deazapurine, the linkage is attached to the 7-position of the 7-deazapurine, and if B is pyrimidine, the linkage is attached to the 5-position of the pyrimidine. Preferably B is selected from the group consisting of uracil, cytosine, deazaadenine, and deazaguanosine. In a seventh aspect, the invention includes a method of polynucleotide sequencing using the dyes of the invention. The method comprises the steps of forming a mixture of a first, a second, a third, and a forth class of polynucleotides such that each polynucleotide in the first class includes a 3'-terrninal dideoxyadenosine and is labeled with a first dye; each polynucleotide in the second class includes a 3'-terminal dideoxycytidine and is labeled with a second dye; each polynucleotide in the third class includes a 3'-teπninal dideoxyguanosine and is labeled with a third dye; and each polynucleotide in the forth class includes a 3 '-terminal dideoxythymidine and is labeled with a forth dye. In the method, one or more of the first, second, third, or forth dyes is an asymmetric benzoxanthene dye of the invention. The other of the dyes is chosen such that they are spectrally resolvable from the asymmetric benzoxanthene dye(s) and from each other. After forming the above mixture, the polynucleotides are electrophoretically separated thereby forming bands of similarly sized polynucleotides. Next, the bands are illuminated with an iUiimination beam capable of causing the dyes to fluoresce. Finally, the classes of the polynucleotides are identified by the fluorescence spectrum of the labeled polynucleotides in each band. In an eighth aspect, the invention includes a method of fragment analysis utilizing the dye compounds of the present invention. The method of this aspect comprises the steps of: forming a labeled polynucleotide fragment, the fragment being labeled with a dye compound of the invention; subjecting the labeled polynucleotide fragment to a size-dependent separation process; and detecting the labeled polynucleotide fragment subsequent to the separation process. The dyes of the present invention provide at least seven important advantages over currently available dyes used for the simultaneous detection of multiple spatially-overlapping analytes, particulariy in the area of multicolor fluorescence-based DNA sequencing. First, the dyes of the present invention are much more stable to DNA synthesis conditions then are presently available dyes having the desired spectral characteristics. This enhanced stability to DNA synthesis conditions makes it possible to more readily prepare labeled oligonucleotide reagents using automated DNA synthesis technologies, e.g., labeled PCR primers, DNA sequencing primers, and oligonucleotide hybridization probes. Second, the dyes of the present invention are significantly more photostable than fluorescein-based dyes previously employed in the wavelength region above about 550 nm. Third, the dyes of the present invention have an absorption spectrum which has a blue "shoulder" thereby permitting more efficient exdtation of the dyes at shorter wavelengths than dibenzoxanthene dyes or rhodamine-based dyes. Fourth, the asymmetric benzoxanthene dyes of the present invention have significantly higher quantum yidds then do spectrally similar rhodamine-based dyes. Fifth, the enhanced exdtation effidency with typical light sources coupled with the high quantum yidds of the dyes of the present invention make the dyes significantly brighter than presently available dyes having the desired spectral characteristics. Brightness is particulariy important in the context of DNA sequencing applications where the amount of analyte is limited by electrophoresis loading factors and the total fluorescence is distributed over hundreds of spatially separated spedes. As used herein the term "brightness" refers to the combined effects of extinction coefficient and fluorescence quantum yidd on ultimate fluorescence emission intensity. By increasing the brightness of the fluorescent labels, the larger, less abundant fragments can be more readily detected and less sample need be loaded into the dectrophoresis, thereby resulting in superior electrophoretic resolution. Moreover, the increased brightness of the analytes contributes to increased signal- to-noise ratio leading to improved deconvolution of spatially and spectrally ndghboring spedes. Sixth, the asymmetry of the dyes of the present invention permits tuning of the emission spectrum of the dyes by varying the substituents R1-R9, particulariy substituents R1-R3 on the resorcinol-derived portion of the dye. Only one equivalent substituent position is available on symmetric dibenzoxanthene compounds, thereby greatly limiting the degrees of freedom available for spectral tuning of the dyes. Seventh, the dyes of the invention are readily converted to stable phosphoramidite derivatives which can be employed in the automated chemical synthesis of labded oligonucleotides. These and other objects, features, and advantages of the present invention will become better understood with reference to the following description, drawings, and appended claims. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows the structures of various fluorescent dyes previously employed as long-wavelength labels, i.e., labels emitting above 550 nm. FIGS. 2A and 2B depict a preferred synthesis of the asymmetric benzoxanthene dyes of the invention. FIG. 3 shows a preferred synthesis of oligonucleotides labeled with the dyes of the invention. FIG. 4 shows the excitation spectra of TAMRA (22) - and Cl-FLAN (2)-labeled oligonucleotides. FIG. 5 shows a comparison of the quantum yields of TAMRA (22)- and Cl-FLAN (2)-labeled oligonucleotides. FIG. 6 shows a comparison of the eqimolar emission intensity of TAMRA (22)- and Cl-FLAN (2)-labeled oligonucleotides. FIG. 7 shows fluorescence emission spectra for members of a 4-plex set of dye- labeled DNA sequencing primers. FIG. 8 shows a synthesis of a 2-fluoro-l,3-dihydroxynapthalene intermediate of the invention. FIG. 9 shows the results of a DNA sequencing experiment employing an oligonucleotide sequendng primer labeled with a dye compound of the invention. FIG. 10 shows the results of a microsatellite analysis employing an oligonucleotide PCR primer labeled with a dye compound of the invention. FIG. 11 shows four preferred synthesis routes for the synthesis of the asymmetric benzoxanthene dyes of the invention. FIG. 12 shows three preferred synthesis routes for the synthesis of the 1- substituted,3-hydroxynapthalene intermediate of the invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Reference will now be made in detail to certain preferred embodiments of the invention. While the invention will be described in conjunction with the preferred embodiments, h will be understood that they are not intended to limit the invention to those embodiments. On the contrary, the invention is intended to cover alternatives, modifications, and equivalents, which may be included within the invention as defined by the appended claims. Generally, the present invention comprises a novd dass of asymmetric benzoxarrthene compounds useful as fluorescent dyes, methods and intermediates for synthesis of such dyes, reagents employing such dyes as molecular labels, and methods utilizing such dyes and reagents in the area of analytical biotechnology. The compounds of the present invention find particular application in the area of multicolor fluorescent DNA sequencing and fragment analysis. I. Asymmetric Benzoxanthene Dve Compounds In a first aspect, the present invention comprises a novd class of asymmetric benzoxanthene dye compounds having the general structure shown in Formula I immediatdy below. (All molecular structures provided herein are intended to encompass not only the exact dectronic structure presented, but also include all resonant structures and protonation states thereof.) FORMULA I In Formula L Yi and Y 2 are either individually hydroxyl, oxygen, amine, imminium or oxygen. When Yi is hydroxyl and Y 2 is oxygen, the compound is analogous to fluorescein, while when Yi is amine and Y 2 is imminium, the compound is analogous to rhodamine. Preferably Yi is hydroxyl and Y 2 is oxygen. Moieties R 1 -R are substituents used to modulate various properties of the dyes by modifying the dectronic structure of the ground and exdted states of the molecule. In particular, varying moieties R 1 -R9 affects the spectral characteristics, chemical stability, and photostability of the compounds. Substituents R 1 -R3 and Ro are particularly important in defining the properties of the compounds of Formula I. For example, h has been observed that placing a fluorine atom at one of positions R 1 -R3 leads to increased chemical and photostabiliry, and that if Ro is substituted phenyl, making substituents X 2 and Xs chlorine leads to narrower emission bands. (See below for the definition of substituents X 2 and X5.) Preferably, substituents Ri-Rg are hydrogen, fluorine, chlorine, lower alkyl, lower alkene, lower alkyne, sulfonate, sulfone, amino, imrriininium, amido, nitrile, aryl, lower alkoxy, linking group, or combinations thereof, where as used herein the term "linking group" refers to a functionality capable of reacting with a "complementary functionality" attached to a reagent, such reaction forming a "linkage" connecting the dye to the reagent. More will be said about particular linking groups, complementary functionalities, and linkages in a subsequent section of this disclosure. Preferably, R] is lower alkoxy, chlorine, fluorine, or hydrogen; R is lower alkyl, fluorine, or chlorine; and R 3 is lower alkyl, or fluorine. More preferably, one of Ri, R 2 , and R 3 is fluorine. In a particulariy preferred embodiment, at least R 3 is fluorine. As used herein, the term "lower alkyl" denotes straight-chain and branched hydrocarbon moieties containing from 1 to 8 carbon atoms, i.e., methyl, ethyl, propyl, isopropyl, tert-butyl, isobutyl, sec-butyl, neopentyl, tert-pentyl, and the like. "Lower substitued alkyl" denotes a lower alkyl including dectron-withdrawing substituents, such as halo, cyano, nitro, sulfo, or the like. "Lower haloalkyl" denotes a lower substituted alkyl with one or more halogen atom substituents, usually fluoro, chloro, bromo, or iodo. "Lower alkene" denotes a hydocarbon containing from 1 to 8 carbon atoms wherein one or more of the carbon-carbon bonds are double bonds, wherein the non-double bonded carbons comprise lower alkyl or lower substituted alkyl. "Lower alkyne" denotes a hydocarbon containing from 1 to 8 carbon atoms wherein one or more of the carbons are bonded with a triple bond, wherein the non-triple bonded carbons comprise lower alkyl or lower substituted alkyl. "Sulfonate" refers to moieties induding a sulfur atom bonded to 3 oxygen atoms, inducting mono- and di-salts thereof, e.g., sodium sulfonate, potassium sulfonate, disodium sulfonate, and the like. "Amino" refers to moieties including a nitrogen atom bonded to 2 hydrogen atoms, lower alkyl moieties, or any combination thereof "Amido" refers to moieties including a carbon atom double bonded to an oxygen atom and single bonded to an amino moiety. "Nitrile" refers to moieties induding a carbon atom triple bonded to a nitrogen atom. "Lower Alkoxy" refers to a moiety including lower alkyl single bonded to an oxygen atom. "Aryl" refers to single or multiple phenyl or substituted phenyl, e.g., benzene, naphthalene, anthracene, biphenyl, and the like. Preferably Ro is acetylene, lower alkyl, lower alkene, cyano, phenyl or substituted phenyl, heterocyclic aromatic, or combinations thereof, the substituted phenyl having the structure: wherein X1-X5 taken separately are hydrogen, chlorine, fluorine, lower alkyl, carboxyiic add, sulfonic add, -CH 2 OH, or linking group. As used herein, the term "heterocyclic aromatic" refers to aromatic moieties having a heteroatom as part of the cyclic structure, e.g., pyrole, furan, indole, and the like. Preferably, Xi is carboxyiic add, sulfonic a id, or -CH 2 OH; X 2 and Xj taken separately are hydrogen, chlorine, fluorine, or lower alkyl; and X 3 and X 4 taken separately are hydrogen, chlorine, fluorine, lower alkyl, carboxyiic add, sulfonic add, or linking group. More preferably, X 2 and Xj are chlorine. In an additional preferred embodiment, one of X3 or Xt is linking group. Preferably, Xi is carboxyiic add. In an additional preferred embodiment particulariy suited to forming phosphoramidite compounds induding the dye compound of the invention, one of Xi or Xs is a moiety which is capable of forming a cyclic ester or cyclic ether, e.g., carboxyiic add, sulfonic add, or -CH2OH, or any other group that will form a spirocyclic system, i.e., bicyclic compounds having one carbon atom common to both rings, e.g., spiro[4.5]decane. Preferably the linking group of the invention is isothiocyanate, sulfonyl chloride, 4,6- dichlorotriazinylamine, succinimidyl ester, or other active carboxylate whenever the complementary functionality is amine. Preferably the linking group is maleimide, halo acetyl, or iodoacetamide whenever the complementary functionality is sulfhydryl. See R. Haugland, Molecular Probes Handbook of Fluorescent Probes and Research Chemicals, Molecular probes, Inc. (1992). In a particularly preferred embodiment, the linking group is an activated N- hydroxysuccinimidyl (NHS) ester which reacts with an amine complementary functionality, where to form the activated NHS ester, a dye of the invention including a carboxylate linking group is reacted with dicydohexylcarbodii ide and N-hydroxysuccinimide to form the NHS ester. See FIG. 3. Several alternative generalized methods may be used to synthesize the asymmetric benzoxanthene dye compounds of the present invention, four of which will be described here with reference to FIG. 11. In a first preferred method referred to in FIG. 11 as Route A, compound 27 is reacted with 1,3-dihydroxy or 1,3-aminohydroxy benzene derivative 28 and 1,3 -dihydroxy or 1,3-aminohydroxy naphthalene derivative 29 employing equal equivalents of each under acid catalysis and heat to give asymmetric dye compound 30. Preferably compound 27 is a cyclic or straight chain anhydride, e.g., LVG is OCOR 9 ; ester, e.g., where LVG is OR where R is lower alkyl, phenyl, or sulfonate; or acid chloride, e.g., where LVG is chlorine or other halogen. In an alternative preferred synthesis method referred to as Route B in FIG. 11, compound 27 is reacted with 2 equivalents of a 1,3-dihydroxybenzene derivative, i.e., Yi is hydroxy, or a 1 ,3-aminohydroxybenzene derivative, i.e., Yi is amino, 28 to give symmetric xanthene dye 31. Compound 31 is then decomposed by base hydrolysis to form intermediate benzoyl condensation product 32. Condensation product 32 is then reacted under acid catalysis and heat with compound 29 to give asymmetric dye 30, where 29 is 1,3-dihydroxynaphthalene when Y 2 is hydroxy, or 1,3-aminohydroxynaphthalene when Y2 is amino. In yet a third generalized synthesis method, referred to as Route C in FIG. 11, compound 27 is reacted with 1 equivalent of 28 with heat to give intermediate benzoyl condensation product 32. Compound 32 is then reacted with 29 under acid catalysis and heat to give asymmetric dye 30. In a fourth generalized synthesis method, referred to as Route D in FIG. 11, equal equivalents of compound 33, compound 28, and compound 29 are reacted under acid catalysis and heat to give asymmetric xanthone intermediate 34. Preferably 33 is a carbonate, e.g., LVG is OR where R is preferably lower alkyl or phenyl; or formate, e.g., where LVG is halogen and OR where R is preferably lower alkyl or phenyl. Compound 34 is then reacted with an anionic organometallic R 9 derivative to give the asymmetric dye 30, e.g., RoLi, RoMgX where X is halide, e.g., Br, CI, I, and the like. FIGS. 2A and 2B show the synthesis of a set of particularly preferred asymmetric dye compounds of the invention. In this synthesis, a 1,3 dihydroxynapthalene derivative, such as 1,3-dihydroxynapthalene (9b) or 2-fluoro-l,3-dihydroxynapthalene (9a), is reacted with 1 equivalent of a phthallic anhydride derivative, e.g., 3,6-dichlorotrimelletic add anhydride (10a), and one equivalent of a resorcinol derivative (lla, lib, lie, or lid), and heated for 16 hours in neat organic add, e.g., MeSO3H under argon. The crude dye is then preαpitated by addition to an ice / water mixture and isolated by filtration. The crude dye is then further purified into 2 isomers 1 and 2 by preparative thin layer chromatography. Unsubstituted derivatives of the asymmetric benzoxanthene dyes (R and/or R 3 is H) may be reacted further with halogenating reagents, e.g., commerdaUy available sources of positive fluorine, NaOCl, NaOH / Br 2 , NaOH / I 2 , to produce quantitativdy halogenated derivatives, e.g., R 2 = R 3 = CL, Br, L or F after extractive workup with 10 % HCl / EtOAc, drying with Na 2 SO 4 , filtering, and concentrating in vacuo. See inset in FIG. 2B. π. Substituted Naphthalene Intermediates In a second aspect, the present invention comprises novel intermediate compounds useful for the synthesis of the asymmetric benzoxanthene compounds of the subject invention, such intermediate having the general structure shown in Formula II immediatdy bdow. In particular, the intermediate compounds of the invention enable the synthesis of asymmetric benzoxanthene compounds with regio-sdective incorporation of substituents, e.g., halogen atoms, at the 2-position of 2-substituted asymmetric benzoxanthene compounds, where the 2- position corresponds to the R 3 position in the compounds of Formulas I and 13. FORMULA π Substituents R 3 -R 7 in the structure of Formula II correspond to like-numbered substituents in the structure of Formula I described above, and Y 2 is hydroxyl or amine. Preferably, R3 is fluorine and Y 2 is hydroxyl. FIG. 12 shows three alternative generalized synthesis schemes for the synthesis of the substituted naphthalene intermediates of the invention. In a first method indicated as Route A in FIG. 12, substituted ester enolate derivative 35 is reacted with activated homophthallic acid ester derivative 36 to give β-keto-ester derivative 37, e.g., by spontaneous loss of CO 2 when R' is carboxylate. Preferably in compound 35, R' is hydrogen, carboxylate, or halogen and R is lower alkyl. Preferably in compound 36, LVG is halogen, N- hydroxysucdnimide, phenoxide, hydroxybenzotriazole, or carboxylate. Compound 37 is then cyclized under base catalysis and heat to give substituted 1,3-naphthalene diol 38, i.e., Y 2 is OH. In a second preferred synthesis method indicated as Route B in FIG. 12, compound 35 is reacted with activated phenylacetate derivative 39, where LVG is as described above for compound 36 in Route A, to give β-keto-ester derivative 40, e.g., by spontaneous loss of CO 2 when R' is carboxylate. Compound 40 is then cyclized under acid catalysis and heat to give substituted 1,3-naphthalene diols 38, i.e., Y is OH. In a third preferred synthesis method indicated as Route C, compound 35 is reacted with cyano-phenyl acetate derivatives 41, where LVG is as described above for compound 36 in Route A, to give cyano β-keto-ester derivatives 42, e.g., by spontaneous loss of CO 2 when R' is carboxylate. Compound 42 is then cyclized under base catalysis and heat to give substituted l-amino-3-hydroxynaphthaIenes 38, i.e., Y 2 is NH 2 . m Reaflfntfi Utiliτiηg Dye Compounds In another aspect, the present invention comprises reagents labeled with the asymmetric benzoxanthene dye compounds of Formula I. Reagents of the invention can be virtually anything to which the dyes of the invention can be attached. Preferably the dyes are covalently attached to the reagent. Reagents include proteins, polypeptides, polysaccharides, nucleotides, nucleosides, porynudeotides, lipids, solid supports, organic and inorganic polymers, and combinations and assemblages thereof, such as chromosomes, nuclei, living cells, such as bacteria, other microorganisms, mammalian cells, tissues, and the like. A, Nucleotide Reagents A preferred class of reagents of the present invention comprise nucleotides and nudeosides which incorporate the asymmetric benzoxanthene dyes of the invention. Such nucleotide reagents are particularly useful in the context of labeling polynucleotides formed by enzymatic synthesis, e.g., nucleotide triphosphates used in the context of PCR amplification, Sanger-type polynucleotide sequencing, and nick-translation reactions. As used herein, "nucleoside" refers to a compound consisting of a purine, deazapurine, or pyrimidine nucleoside base, e.g., adenine, guanine, cytosine, uracil, thymine, deazaadenine, deazaguanosine, and the like, linked to a pentose at the 1' position, including 2'-deoxy and 2'- hydroxyl forms, e.g. as described in Komberg and Baker, DNA Replication, 2nd Ed. (Freeman, San Frandsco, 1992). The term "nucleotide" as used herein refers to a phosphate ester of a nucleoside, e.g., triphosphate esters, wherein the most common site of esterification is the hydroxyl group attached to the C-5 position of the pentose. "Analogs" in reference to nucleosides include synthetic nucleosides having modified base moieties and/or modified sugar moieties, e.g. described generally by Scheit, Nucleotide Analogs (John Wiley, New York, 1980). The term "labeled nucleoside" refers to nucleosides which are covalently attached to the dye compounds of Formula I through a linkage. Preferred nucleotides of the present invention are shown bdow in Formula JU wherein FORMULA m B is a nucleotide base, e.g., uracil, cytosine, deazaadenine, and deazaguanosine. Wi and W 2 taken separately are H or OH. W 3 is OH, , including associated counterions if present, e.g., H, Na, NH^ and the like. D is a dye compound of Formula I. In one particularly preferred embodiment, the nucleotides of the present invention are dideoxynucleotide triphosphates having the structure shown in Formula HI.1 below, induding associated counterions if present. FORMULA m i Labeled dideoxy nudeotides such as that shown in Formula Lu.1 find particular application as chain terminating agents in Sanger-type DNA sequencing methods. In a second particularly preferred embodiment, the nucleotides of the present invention are deoxynucleotide triphosphates having the structure- shown in Formula DT.2 bdow, including assodated counterions if present. FORMULA m.2 Labeled deoxynudeotides such as that shown in Formula LU.2 find particular application as means for labeling polymerase extension products, e.g., in the polymerase chain reaction. When B is purine or 7-deazapurine, the sugar moiety is attached at the ^-position of the purine or deazapurine, and when B is pyrimidine, the sugar moiety is attached at the N 1 - position of the pyrimidine. The linkage .inking B and D is attached to D at one of positions R1-R9 . Preferably, the linkage is not attached at Rι-R 3 . When the dyes of the invention are synthesized from trimelletic anhydride, Ro is preferably substituted phenyl and the linkage is attached to the dye at one of the X 3 or X4 positions of the substituted phenyl the other position being a hydrogen atom. When B is a purine, the linkage linking B and D is attached to the 8-position of the purine, when B is 7-deazapurine, the linkage is attached to the 7-position of the 7-deazapurine, and when B is pyrimidine, the linkage is attached to the 5-position of the pyrimidine. Nucleoside labeling can be accomplished using any of a large number of known nucleoside labeling techniques using known linkages, linking groups, and associated complementary functionalities. The linkage linking the dye and nucleoside should (i) be stable to oligonucleotide synthesis conditions, (ii) not interfere with oligonucleotide-target hybridization, (iii) be compatible with relevant enzymes, e.g., polymerases, ligases, and the like, and (iv) not quench the fluorescence of the dye. Preferably, the dyes are covalently linked to the 5-carbon of pyrimidine bases and to the 7-carbon of 7-deazapurine bases. Several suitable base labeling procedures have been reported that can be used with the invention, e.g. Gibson et al, Nucleic Acids Research, 15:6455-6467 (1987); Gebeyehu et aL Nucleic Acids Research, 15: 4513-4535 (1987); Haralambidis et al, Nucleic Acids Research, 15: 4856-4876 (1987); Nelson et al., Nucleosides and Nucleotides, 5(3): 233-241 (1986); Bergstrom, et al., JACS, 111: 374-375 (1989); U.S. Patent Nos. 4,855,225, 5,231,191, and 5,449,767. Accordingly, these references are incorporated by reference. Preferably, the linkages are acetylenic amido or alkenic amido linkages, the linkage between the dye and the nucleotide base being formed by reacting an activated N- hydroxysuccinirnide (NHS) ester of the dye with an alkynylamino- or alkenylamino-derivatized base of a nucleotide. More preferably, the resulting linkage is 3-(carboxy)amino-l-propynyl or 3-amino-l-propyn-l-yl (Formula HI.3). Several preferred linkages for linking the dyes of the invention to a nucleoside base are shown below in Formulas m.3, m.4, and HI.5. FORMULA m.4 FORMULA m.5 The synthesis of alkynylarn o-derivatized nudeosides is taught by Hobbs et al. in European Patent Application No. 87305844.0, and Hobbs et al., J. Org. Chem., 54: 3420 (1989), which is incorporated herein by reference. Briefly, the alkynyiamino-derivatized nucleotides are formed by placing the appropriate halodideoxynucleoside (usually 5- iodopyrimidine and 7-iodo-7-deazapurine dideoxynudeosides as taught by Hobbs et al. (cited above)) and Cu(ι) in a flask, flushing with argon to remove air, adding dry DMF, followed by addition of an alkynylamine, triethyl-amine and Pd(0). The reaction mixture can be stirred for several hours, or until thin layer chromatography indicates consumption of the halodideoxynucleoside. When an unprotected alkynylamine is used, the alkynylamino- nudeoside can be isolated by concentrating the reaction mixture and chromatographing on silica gd using an duting solvent which contains ammonium hydroxide to neutralize the hydrohalide generated in the coupling reaction. When a protected alkynylamine is used, methanol/methylene chloride can be added to the reaction mixture, followed by the bicarbonate form of a strongly basic anion exchange resin. The slurry can then be stirred for about 45 minutes, filtered, and the resin rinsed with additional methanol/methylene chloride. The combined filtrates can be concentrated and purified by fiash-chromatography on silica gd using a methanol-methylene chloride gradient. The triphosphates are obtained by standard techniques. B. Phosphoramidite Reagents Another preferred class of reagents comprise phosphoramidite compounds which incoφorate the asymmetric benzoxanthene dyes of the invention. Such phosphoramidite reagents are particularly useful for the automated chemical synthesis of polynucleotides labded with the asymmetric benzoxanthene dyes of the invention. Such phosphoramidite compounds when reacted with a 5 '-hydroxyl group of a nucleotide or polynucleotide form a phosphite ester linker which, in turn, is oxidized to give a phosphate ester linker, e.g., U.S. Patent Nos. 4,458,066 and 4,415,732, both patents hereby incorporated by reference. 1. Non-nucleotide Phosphoramidite Reagents: Generally, in one aspect, the phosphoramidite reagents of the invention have the structure of Formula IV immediatdy below, FORMULA IV where X is a spacer arm; D is an asymmetric benzoxanthene dye of Formula I or a protected derivative thereof; Y is a linkage formed with a linking group on the dye; Bi is a phosphite ester protecting group, and B 2 , and B 3 taken separatdy are lower alkyl, lower alkene, lower aryl having between 1 and 8 carbon atoms, aralkyl, or cycloalkyl containing up to 10 carbon atoms. Non-nucleotidic phosphoramidites as shown in Formula IV are particulariy well suited for labeling the 5 '-end of a chemically-synthesized polynucleotide through the sugar-portion of the nucleotide. Spacer X and linkage Y may take a variety of forms, however, the structure X-Y must be such that (i) it is stable to DNA synthesis conditions, (ii) does not interfere with oligonucleotide-target hybridization, and (iϋ) does not quench the fluorescence of the dye to which it is attached, e.g., U.S. Patent Nos. 5,231,191, 5,258,538, and 4,757,141, 5,212,304, all patents hereby incorporated by reference. Preferably X is linear or cyclic lower alkyl, linear or cyclic substituted lower alkyl, polyethlene oxide, lower aryl having between 1 and 8 carbon atoms, peptide, or polyether. Preferably the linkage Y is amido, sulfonamido, urea, urethane, or thourea. In one particularly preferred embodiment, the linkage Y is amido and the spacer X is linear alkyl having the structure below in Formula IV.1 FORMULA IV.1 where n is from 2 to 30, preferably from 2 to 10, and more preferably from 2 to 6. In a second particularly preferred embodiment, the linkage Y is amido and the spacer X is linear polyethylene oxide having the structure shown below in Formula 1V.2 FORMULA IV.2 where n is from 2 to 30, preferably from 2 to 10, and more preferably from 2 to 6. Preferably, B 2 and B 3 taken together form an alkyl chain containing up to 5 carbon atoms in the prindple chain and a total of up to 10 carbon atoms with both terminal valence bonds of said chains being attached to the nitrogen atom. Alternativdy, B and B 3 taken together with the nitrogen atom form a saturated nitrogen heterocycle which contains one or more heteroatoms sdected from the group consisting of nitrogen, oxygen, and sulfur. Preferably, B 2 and B 3 taken separately are isopropyl, t-butyl, isobutyl, or sec-butyl, and B 2 and B 3 taken together is morphoUino. Bi is a phosphite ester protecting group which prevents unwanted extension of the polynucleotide to which the phosphoramidite is attached. Bi is stable to polynucleotide synthesis conditions yet is able to be removed from the polynucleotide product with a reagent that does not adversely affect the integrity of the polynucleotide or the dye. Preferably, B t is methyl, β-cyanoethyl, or 4-nitrophenylethyl. B 2 and B 3 taken separately are isopropyl, t-butyl, isobutyl, or sec-butyl, and B 2 and B 3 taken together is moφhollino. The linkage linking Y and D is attached to D at one of positions R 1 -R . Preferably, the linkage is not attached at Rι-R 3 . When the dyes of the invention are synthesized from trimelletic anhydride, Ro is preferably substituted phenyl and the linkage is attached to the dye at one of the X 3 or X positions of the substituted phenyl. Such phosphoramidite compounds may be synthesized by known methods. Generally, the synthesis proceeds as follows. Phenolic hydroxyls of the dye are protected with dye- protecting groups that can be removed with a DNA synthesis deprotection agent, e.g., ammonia, ethanolamine, methylamine/ammonium hydroxide mixtures, and mixtures of t- butylamine/water/methanol (1:2:1), e.g., see U.S. Patent no. 5,231,191, hereby incorporated by reference in its entirety. Dyes so protected are referred to herein as "protected derivatives" of the dye. Preferred protecting groups include esters of benzoic add or pivalic add. The linking group of the protected dye, e.g., carboxyiic add, is then activated, e.g., with carbodiimide, and reacted with an alcohol linker derivative, e.g., an amino alcohol, e.g., ethanolamine, hexanol amine, or the like, in N,N-dimethylformaπ-ide (DMF), or another like aprotic solvent to yidd a protected dye with a free alcohol functionality, e.g., alcohol-amide derivative. The free alcohol is then reacted with a phosphitylating agent using standard procedures, e.g., di-<N,N- diisopropylamino)methoxyphosphine in acetonitrile containing catalytic amounts of tetrazole diisopropylamine, to yidd the phosphoramidite, e.g., U.S. Patent No. 5,231, 191. 2. Nucleotidic Phosphoramidite Reagents: Generally, in a second aspect, the phosphoramidite reagents of the invention have the structure of Formula V immediatdy bdow, FORMULA V where Bι-B 3 are as described above, B 5 is hydrogen or a hydroxyl protecting group, B is a nucleotide base, and D is an asymmetric benzoxanthene dye of Formula L or a protected derivative thereof Nucleotide phosphoramidites such as shown in Formula V are particulariy well suited for the internal labeling of chemically-synthesized polynucleotides. When B is purine or 7-deazapurine, the sugar moiety is attached at the N 9 -position of the purine or deazapurine. Altemativdy, when B is pyrimidine, the sugar moiety is attached at the N'-position of the pyrimidine. B and D are linked through a linkage formed by the reaction of a linking group and its complementary functionality, such linkages between dyes and nucleotide bases have been described in detail above. If B is a purine, the linkage is attached to the 8-position of the purine, while if B is 7-deazapurine, the linkage is attached to the 7-position of the 7-deazapurine. If B is pyrimidine, the linkage is attached to the 5-position of the pyrimidine. B5 refers generally to hydrogen or an add-cleavable hydroxyl protecting group. Preferably, Bj is the triphenylmethyl radical and its electron-donaring-substituted derivatives, where, as used herein, the term "electron-donating" denotes the tendency of a substituent to rdease valence electrons to neighboring atoms in the molecule of which it is a part, i.e., it is electropositive with respect to ndghboring atoms. Preferably, electron-donating substituents include amino, lower alkyl, lower aryl having between 1 and 8 carbon atoms, lower alkoxy, and the like. More preferably, the dectron-donating substituents are methoxy. Exemplary trityls indude 4,4'-dimethoxytrityl, i.e. bis(p-anisyl)phenyimethyl, monomethoxytrityl, α- naphthyldiphenylmethyl, tri(p-methoxyphenyl)methyl, and the like. Attachment and deavage conditions for these and other trityls can be found in Greene and Wuts, Protective Groups in Organic Synthesis, 2nd Edition (John Wiley, New York, 1991). Generally, the nucleotide phosphoramidites of the invention may be synthesized as follows. A nucleoside bearing a hydroxyl protecting group on the 5'- hydroxyl and a protected complementary functionality on the base is sdectively deprotected to expose only the complementary functionality. Next, a protected dye (as described above) is activated by converting a linking group into its reactive form. The activated linking group of the dye is then reacted with the complementary functionality of the nucleoside to form the dye labded nucleoside that bears protecting groups on the 5'-hydroxyl (and on the 2*-hydroxyl for the case of RNA) and on the phenolic groups of the dye. The dye labeled nucleoside is then reacted with a phosphitylating agent as described above to produce the nucleotide phosphoramidite. In a preferred method where the complementary functionality is amine and the linking group is carboxyl, the synthesis proceeds as follows. A protected nucleoside bearing a hydroxyl protecting group on the 5'- hydroxl, e.g., a trityl group, and a protected ammo-nitrogen complementary functionality on the base is sdectively deprotected to expose the amine, such sdective deprotection serving to deprotect only the amine functionality without deprotecting the protected 5'-hydroxyl moiety. A protected dye (as described above) is activated by converting a carboxy linking group into its NHS ester with dicyclohexyl carbodiimide and N- hydroxysuccir-imide. The NHS ester is reacted with the amino group of the nucleoside to form the dye labded nucleoside that bears protecting groups on the 5'-hydroxyl (and on the 2'- hydroxyl for the case of RNA) and on the phenolic groups of the dye. The dye labded nucleoside is then reacted with a phosphitylating agent as described above. C. Polynucleotide Reagents Yet another preferred class of reagents of the present invention comprise polynucleotides labded with the asymmetric benzoxanthene dyes of the invention. Such labded polynucleotides are useful in a number of important contexts induding as DNA sequencing primers, PCR primers, oligonucleotide hybridization probes, and the like. As used herein, the terms "polynudeotide" or "oligonucleotide" refer to Imear polymers of natural or modified nucleoside monomers, induding double and single stranded deoxyribonucleosides, ribonudeosides, α-anomeric forms thereof, and the like. Usually the nucleoside monomers are linked by phosphodiester linkages, where as used herein, the term "phosphodiester linkage" refers to phosphodiester bonds or analogs thereof induding phosphorothioate, phosphorodithioate, phosphorosdenoate, phosphorodisdenoate, phosphoroanilothioate, phosphoranilidate, phosphoramidate, and the like, induding associated counterions, e.g., H, NH^ Na, and the like if such counterions are present. The polynudeotides range in size form a few monomeric units, e.g. 8-40, to several thousands of monomeric units. Whenever a polynudeotide is represented by a sequence of letters, such as "ATGCCTG," it will be understood that the nudeotides are in 5'->3' order from left to right and that "A" denotes deoxyadenosine, "C" denotes deoxycytidine, H G" denotes deoxyguanosine, and T" denotes thymidine, unless otherwise noted. The labded polynucleotides of the invention include a nucleotide having the formula: FORMULA VI where B is a 7-deazapurine, purine, or pyrimidine nucleotide base. Zi is H or OH. Z 2 is H, OH, HPO 4 , or Nuc, wherein Nuc refers to a nucleoside or polynucleotide. The nucleoside of Formula VI and Nuc are linked by a phosphodiester linkage, the linkage being attached to the 5 '-position of Nuc. Z 3 is H, HPO 3 , or Nuc, wherein Nuc and the nucleoside are linked by a phosphodiester linkage attached to the 3' -position of Nuc. D is a dye compound of Formula I. Base B is attached to the sugar moiety and to the dye compound as described above for the nucleotide phosphoramidite reagent of the invention. As defined, the labeled nucleotide of Formula VI can be the 5 '-terminal nucleotide, the 3'- terminal nucleotide, or any internal nucleotide of the polynucleotide. In one preferred embodiment, the labeled polynudeotides of the present invention include multiple dyes located such that fluorescence energy transfer takes place between a donor dye and an acceptor dye. Such multi-dye polynudeotides find application as spectrally-tunable sequencing primers, e.g., Ju et al., Proc. Natl. Acad Sci. USA 92: 4347-4351 (1995), and as hybridization probes, e.g., Lee et al. Nucleic Acids Research, 21: 3761-3766 (1993). Labded polynucleotides may be synthesized either enzymatically, e.g., using a DNA polymerase or ligase, e.g., Stiver, Biochemistry, Chapter 24, W.H. Freeman and Company (1981), or by chemical synthesis, e.g., by the phosphoramidite method, the phosphite-triester method, and the like, e.g., Gait, Oligonucleotide Synthesis, IRL Press (1990). Labds may be introduced during enzymatic synthesis utilizing labded nucleotide triphosphate monomers as described above, or introduced during chemical synthesis using labded non-nucleotide or nucleotide phosphoramidites as described above, or may be introduced subsequent to synthesis. Generally, if the labded polynucleotide is made using enzymatic synthesis, the following procedure may be used. A template DNA is denatured and an oligonucleotide primer is annealed to the template DNA. A mixture of deoxynucleotide triphosphates is added to the reaction including dGTP, dATP, dCTP, and dTTP where at least a fraction of one of the deoxynudeotides is labded with a dye compound of the invention as described above. Next, a polymerase enzyme is added under conditions where the polymerase enzyme is active. A labeled polynucleotide is formed by the incorporation of the labded deoxynucleotides during polymerase strand synthesis. In an alternative enzymatic synthesis method, two primers are used instead of one, one primer complementary to the + strand and the other complementary to the - strand of the target, the polymerase is a thermostable polymerase, and the reaction temperature is cycled between a denaturation temperature and an extension temperature, thereby exponentially synthesizing a labded complement to the target sequence by PCR, e.g., PCR Protocols, Innis et al. eds., Academic Press (1990). Labded polynudeotides may be chemically synthesized using the phosphoramidite method. Detailed descriptions of the chemistry used to form polynucleotides by the phosphoramidite method are provided elsewhere, e.g., Caruthers et al., U.S. Pat. No. 4,458,066; Caruthers et al., U.S. Pat. No. 4,415,732; Caruthers et al., Genetic Engineering, 4: 1-17 (1982); Users Manual Model 392 and 394 Polynucleotide Synthesizers, pages 6-1 through 6-22, Applied Biosystems, Part No. 901237 (1991). Accordingly, each of these references are hereby incoφorated by reference in their entirety. The phosphoramidite method of polynucleotide synthesis is the preferred method because of its efficient and rapid coupling and the stability of the starting materials. The synthesis is performed with the growing polynucleotide chain attached to a solid support, so that excess reagents, which are in the liquid phase, can be easily removed by filtration, thereby eliminating the need for purification steps between cycles. The following briefly describes the steps of a typical polynucleotide synthesis cycle using the phosphoramidite method. First, a solid support including a protected nucleotide monomer is treated with add, e.g., trichloroacetic add, to remove a 5 '-hydroxyl protecting group, freeing the hydroxyl for a subsequent coupling reaction. An activated intermediate is then formed by simultaneously adding a protected phosphoramidite nucleoside monomer and a weak acid, e.g., tetrazole, to the reaction. The weak acid protonates the nitrogen of the phosphoramidite forming a reactive intermediate. Nucleoside addition is complete within 30 s. Next, a capping step is performed which terminates any polynucleotide chains that did not undergo nucleoside addition. Capping is preferably done with acetic anhydride and 1-methylimidazole. The internucleotide linkage is then converted from the phosphite to the more stable phosphotriester by oxidation using iodine as the preferred oxidizing agent and water as the oxygen donor. After oxidation, the hydroxyl protecting group is removed with a protic add, e.g., trichloroacetic acid or dichloroacetic acid, and the cycle is repeated until chain elongation is complete. After synthesis, the polynucleotide chain is cleaved from the support using a base, e.g., ammonium hydroxide or t-butyl amine. The cleavage reaction also removes any phosphate protecting groups, e.g., cyanoethyl. Finally, the protecting groups on the exocyclic amines of the bases and the hydroxyl protecting groups on the dyes are removed by treating the polynucleotide solution in base at an elevated temperature, e.g., 55 °C. Any of the phosphoramidite nucleoside monomers may be dye-labeled phosphoramidites as described above. If the 5 '-terminal position of the nucleotide is labeled, a labeled non-nucleotidic phosphoramidite of the invention may be used during the final condensation step. If an internal position of the oligonucleotide is to be labeled, a labeled nucleotidic phosphoramidite of the invention may be used during any of the condensation steps. Subsequent to synthesis, the polynucleotide may be labded at a number of positions induding the 5'-terminus, e.g., Oligonucleotides and Analogs, Eckstein ed., Chapter 8, IRL Press (1991) and Orgd et al., Nucleic Acids Research 11(18): 6513 (1983); U.S. Patent No. 5,118,800, hereby incorporated by reference; the phosphodiester backbone, e.g., ibid., Chapter 9; or at the 3 '-terminus, e.g., Ndson, Nucleic Acids Research 20(23): 6253-6259, and U.S. Patent Nos. 5,401,837 and 5,141,813, both patents hereby incorporated by reference. For a review of oligonucleotide labeling procedures see R. Haugland in Excited States of Biopofymers, Sterner ed., Plenum Press, NY (1983). In one preferred post-synthesis chemical labeling method an oligonuleotide is labded as follows. A dye including a carboxy linking group is converted to the n-hydroxysuαanimide ester by reacting with approximately 1 equivalent of 1,3-dicyclohexyJcarbodiimide and approximately 3 equivalents of n-hydroxysucάriimide in dry ethyl acetate for 3 hours at room temperature. The reaction mixture is washed with 5 % HCl, dried over magnesium sulfate, filtered, and concentrated to a solid which is resuspended in DMSO. The DMSO dye stock is then added in excess (10-20 x) to an aminohexyl derivatized oligonucleotide in 0.25 M bicarbonate carbonate buffer at pH 9.4 and allowed to react for 6 hours, e.g., U.S. Patent No. 4,757,141. The dye labded oligonucleotide is separated from unreacted dye by passage through a size-exclusion chromatography column duting with buffer, e.g., 0.1 molar triethylamine acetate (TEAA). The fraction containing the crude labeled oligonucleotide is further purified by reverse phase HPLC employing gradient dution. IV. Methods I Itiliπng the Compounds and Reagents of the Invention The dyes and reagents of the present invention are well suited to any method utilizing fluorescent detection, particularly methods requiring the simultaneous detection of multiple spatially-overlapping analytes. Dyes and reagents of the invention are particularly well suited for identifying classes of polynudeotides that have been subjected to a biochemical separation procedure, such as dectrophoresis, where a series of bands or spots of target substances having similar physiochemical properties, e.g. size, conformation, charge, hydrophobidty, or the like, are present in a linear or planar arrangement. As used herein, the term "bands" includes any spatial grouping or aggregation of analytes on the basis of similar or identical physiochemical properties. Usually bands arise in the separation of dye-polynucleoode conjugates by dectrophoresis. Classes of polynudeotides can arise in a variety of contexts. In a preferred category of methods referred to herein as "fragment analysis" or "genetic analysis" methods, labded polynudeotide fragments are generated through template-directed enzymatic synthesis using labded primers or nudeotides, e.g., by ligation or polymerase-directed primer extension; the fragments are subjected to a size-dependent separation process, e.g., dectrophoresis or chromatography; and, the separated fragments are detected subsequent to the separation, e.g., by laser-induced fluorescence. In a particulariy preferred embodiment, multiple classes of polynucleotides are separated simultaneously and the different classes are distinguished by spectrally resolvable labels. One such fragment analysis method known as amplified fragment length polymoφhisim detection (AmpFLP) is based on amplified fragment length polymoφhisms, i.e., restriction fragment length polymoφhisms that are amplified by PCR. These amplified fragments of varying size serve as linked markers for following mutant genes through families. The closer the amplified fragment is to the mutant gene on the chromosome, the higher the linkage correlation. Because genes for many genetic disorders have not been identified, these linkage markers serve to help evaluate disease risk or paternity. In the AmpFLPs technique, the polynudeotides may be labeled by using a labeled polynucleotide PCR primer, or by utilizing labded nucleotide triphosphates in the PCR. In another such fragment analysis method known as nick translation, a reaction is used to replace unlabded nucleoside triphosphates in a double-stranded DNA molecule with labded ones. Free 3'-hydroxyl groups are created within the unlabded DNA by "nicks" caused by deoxyribonuclease I (DNAase I) treatment. DNA polymerase I then catalyzes the addition of a labded nucleotide to the 3 -hydroxyl terminus of the nick. At the same time, the 5' to 3'- exonuclease activity of this enzyme eliminates the nucleotide unit from the 5'-phosphoryi terminus of the nick. A new nudeotide with a free 3 '-OH group is incorporated at the position of the original exdsed nudeotide, and the nick is shifted along by one nudeotide unit in the 3' direction. This 3' shift will result in the sequential addition of new labded nucleotides to the DNA with the removal of existing unlabded nucleotides. The nick-translated polynucleotide is then analyzed using a separation process, e.g., dectrophoresis. Another exemplary fragment analysis method is based on variable number of tandem repeats, or VNTRs. VNTRs are regions of double-stranded DNA that contain adjacent multiple copies of a particular sequence, with the number of repeating units being variable. Examples of VNTR lod are pYNZ22, pMCTl 18, and Apo B. A subset of VNTR methods are those methods based on the detection of microsatellite repeats, or short tandem repeats (STRs), i.e., tandem repeats of DNA characterized by a short (2-4 bases) repeated sequence. One of the most abundant interspersed repetitive DNA families in humans is the (dC-dA)n-(dG-dT)n dinucleotide repeat family (also called the (CA)n dinucleotide repeat family). There are thought to be as many as 50,000 to 100,000 (CA)n repeat regions in the human genome, typically with 15-30 repeats per block. Many of these repeat regions are polymoφhic in length and can therefore serve as useful genetic markers. Preferably, in VNTR or STR methods, label is introduced into the polynucleotide fragments by using a dye-labded PCR primer. In a particularly preferred fragment analysis method, classes identified in accordance with the invention are defined in terms of terminal nucleotides so that a correspondence is established between the four possible terminal bases and the members of a set of spectrally resolvable dyes. Such sets are readily assembled from the dyes of the invention by measuring emission and absoφtion bandwidths with commercially available spectrophotometers. More preferably, the classes arise in the context of the chemical or chain termination methods of DNA sequencing, and most preferably the classes arise in the context of the chain termination method, i.e., dideoxy DNA sequencing, or Sanger sequencing. This method involves the synthesis of a DNA strand by a DNA polymerase in vitro using a single-stranded or double-stranded DNA template whose sequence is to be determined. Synthesis is initiated at only the one site where an oligonucleotide primer anneals to the template. The synthesis reaction is terminated by incorporation of a nudeotide analog that will not support continued DNA elongation. The chain-terTninating nudeotide analogs are the 2',3'-dideoxynucleoside 5'- triphosphates (ddNTPs) which lack the 3'-OH group necessary for 3 * to 5' DNA chain dongation. When proper proportions of dNTPs (2'-deoχynucleoside 5'-triphosphates) and one of the four ddNTPs are used, enzyme-catalyzed polymerization will be terminated in a fraction of the population of chains at each site where the ddNTP can be incorporated. If labded primers or labeled ddNTPs are used for each reaction, the sequence information can be detected by fluorescence after separation by high-resolution dectrophoresis. In the chain termination method, dyes of the invention can be attached to either sequencing primers or dideoxynucleotides. Dyes can be linked to a complementary functionality on the 5' end of the primer, e.g. following the teaching in Fung et al, U.S. Pat. No. 4,757,141 which is incorporated herein by reference; on the base of a primer, or on the base of a dideoxynudeotide, e.g. via the alkynylamino linking groups disclosed by Hobbs et al, European patent application number 87305844.0 which is discussed above and incorporated herein by reference. In each of the above fragment analysis methods labded polynudeotides are preferably separated by dectrophoretic procedures, e.g. Gould and Matthews, dted above; Rickwood and Hames, Eds., Gel Electrophoresis of Nucleic Acids: A Practical Approach, (IRL Press Limited, London, 1981); or Osterman, Methods of Protein and Nucleic Acid Research, Vol. 1 Springer- Verlag, Berlin, 1984). Preferably the type of dectrophoretic matrix is crosslinked or uncrosslinked polyacrylamide having a concentration (wdght to volume) of between about 2-20 wdght percent. More preferably, the polyacrylamide concentration is between about 4-8 percent. Preferably in the context of DNA sequencing in particular, the electrophoresis matrix includes a strand separating, or denaturing, agent, e.g., urea, formamide, and the like. Detailed procedures for constructing such matrices are given by Maniatis et al., "Fractionation of Low Molecular Wdght DNA and RNA in Polyacrylamide Gels Cor-taining 98% Formamide or 7 M Urea," vn Methods in Enzymology, 65: 299-305 (1980); Maniatis et al., "Chain Length Determination of Small Double- and Single-Stranded DNA Molecules by Poryacrylamide Gd Electrophoresis," Biochemistry, 14: 3787-3794 (1975); Maniatis et al., Molecular Cloning: A Laboratory Manual (Cold Spring Harbor Laboratory, New York, 1982), pgs. 179-185; and ABI PRISM 7 " 377 DNA Sequencer User's Manual, Rev. A, January 1995, Chapter 2 (p n 903433, The Perkin-Elmer Corporation, Foster City, CA). Accordingly these references are incorporated by reference. The optimal polymer concentration, pH, temperature, concentration of denaturing agent, etc. employed in a particular separation depends on many factors, including the size range of the nucldc adds to be separated, their base compositions, whether they are single stranded or double stranded, and the nature of the classes for which information is sought by dectrophoresis. Accordingly application of the invention may require standard preliminary testing to optimize conditions for particular separations. By way of example, oligonucleotides having sizes in the range of between about 20-300 bases have been separated and detected in accordance with the invention in the following matrix: 6 percent polyacrylamide made from 19 parts to 1 part acrylamide to bis-acrylamide, formed in a Tris-borate EDTA buffer at pH 8.3. Subsequent to electrophoretic separation, the dye-polynudeotide conjugates are detected by measuring the fluorescence emission from the dye labded polynucleotides. To perform such detection, the labded polynudeotides are illuminated by standard means, e.g. high intensity mercury vapor lamps, lasers, or the like. Preferably the illumination means is a laser having an illumination beam at a wavdength between 488 and 550 nm. More preferably, the dye-polynucleotides are illuminated by laser light generated by an argon ion laser, particulariy the 488 and 514 nm emission lines of an argon ion laser, or an the 532 emission line of a neodymium solid-state YAG laser. Several argon ion lasers are available commercially which lase simultaneously at these lines, e.g. Cyonics, Ltd. (Sunnyvale, Calif.) Model 2001, or the like. The fluorescence is then detected by a light-sensitive detector, e.g., a photomultiplier tube, a charged coupled device, or the like. IV. Examples The invention will be further clarified by a consideration of the following examples, which are intended to be purely exemplary of the invention and not to in any way limit its scope. Unless otherwise indicated, all chemicals were obtained from Aldrich Chemical Company (Milwaukee, WI) and used as purchased. 3-Fluororesordnol (lla) was synthesized from 2,4-dimethoxyaniline according to the literature procedure (Perkin, J. Chem Soc. 110: 1658-1666 (1980)). 2-Chloro-4-methoxyresorcinol (lie) was synthesized from 3-hydroxy-4- methoxy-benzaldehyde according to U.S. Patent No. 4,318,846. 3,6-Dichlorotrimellitic add was synthesized according to U.S. Patent No. 4,318,846, and converted to the anhydride 10a by refluxing in neat acetic anhydride for 4 hours and predpitation of the cooled mixture with diethyl ether. Ethyl hydrogen fluoromalonate was synthesized from diethyl fluoromalonate according to the literature (Org. Syn. Coll. 4: 417-419 (1963)). Ethyl tributylptospoπium-fluoroacetate (19) was synthesized according to the literature {Jet Lett. 30: 6113 (1980)). 2-Fluoro-l,3- dihydroxynapthalene (9a) was synthesized as described in the present disclosure. Dry dichloromethane (CH 2 C1 2 ) was distilled from caldum hydride and tetrahydrofuran (THF) from lithium aluminum hydride (LAH) prior to use. Absolute ethanol was used as purchased or dried by distillation from sodium and stored over activated molecular sieves. Dry ethyl acetate (EtOAc) was distilled from P 2 O 5 after pre-drying with MgSO . Dry dimethyfformamide (DMF) was distilled after pre-drying with magnesium sulfate and stored over activated molecular sieves. All reactions were run under anhydrous conditions under dry argon. Reactions were monitored by thin layer chromatography (TLC) (Silica gd 60, A IM ). Flash chromatography was performed on silica gd 60 (200-400 mesh, Baxter). Final purification of the asymmetric benzoxanthene dyes to give the pure isomers, designated "l" and "2", employed preparative TLC on silica gel 60 PTLC plates (EM Sdence) eluting with CH∑Cfe : MeOH : AcOH (7 : 3 : 0.1). Pure dye isomers were identified by giving a single spot on TLC employing CH 2 C1 2 : MeOH : AcOH (7 : 3 : 0.1) and visualizing with short and long-wavelength UV irradiation. Isomer 2 runs slower on both normal and reverse-phase media. Intermediate products were identified by 'HNMR spectra on a Varian 300 MHz NMR. Absorption spectra of the purified dyes were recorded on a Hewlett Packard 8451 A diode array spectrophotometer, and fluorescence emission spectra were recorded on a PerkLn Elmer LS 50-B luminescence spectrophotometer. HPLC purification of dye labded oligonucleotides was performed on a Perkin-Elmer 200 series pump, connected to a PE LC 240 fluorescence detector, and a PE LC 295 UV/VIS detector, connected to a 2 channd PE 1022 integrator. Buffers employed for dye labded oligonudeotide purification and identification include tris(hydroxymethyl) aminomethane / borate / EDTA (TBE), tris ydroxyrnethyl) aminomethane / EDTA (TE), triethylammonium acetate (TEAA). Buffers are stored as 10 x solutions at 0 °C and diluted fresh before use. HPLC purification employed a reverse-phase RP-18 column. EXAMPLE 1 Synthesis of Asymmetric Benzoxanthenes Compounds 1-7 in FIGS. 2A and 2B were synthesized by reacting a 1,3 dihydroxynapthalene derivative, such as 1,3-dihydroxynapthalene 9b or 2-fluoro-l,3- dihydroxynapthalene 9a (0.2 mole), with 1.1 equivalent of the phthallic anhydride derivative 3,6- dichlorotrimelletic add anhydride 10a, and one equivalent of a resorcinol derivative 11 (0.2 mole), lla, lib, lie, or lid depending on the final product desired, and heated for 16 hours in neat MeSOaH (3 ml) at 110 °C under Argon. The crude dye (a mixture of regioisomers in reactions employing 10a) was predpitated by addition to an ice / water mixture and isolated by filtration. The crude dye was purified into 2 isomers 1 and 2 by preparative thin layer chromatography duting with a mixture of CH2CI2 : MeOH : Acetic Add (70 : 30 : 1). The inset in FIG. 2B shows that R 2 and/or R3 unsubstituted (Rr= R 3 = H) derivatives of the asymmetric benzoxanthene dyes, shown for isomer 2 of dye 5, react further with halogenating reagents (NaOCl, NaOH / Br∑, NaOH / I 2 ) at 0 °C for 3 hours to produce quantitatively the halogenated derivatives such as 8 (R2= R3= CI, Br, L F) after extractive workup with 10 % HCl / EtOAc, drying with Na 2 SO , filtering, and concentrating in vacuo. EXAMPLE 2 Synthesis of Dye-labeled Oligonucleotides The synthesis of dye labded oligonudeotides of the invention will be described with reference to FIG. 3. Cl-FLAN, dye 2, was converted to the n-hydroxysuccinimide ester 12 by reacting with 1.2 equivalents of 1,3-dicyclohexylcarbodiirnide and 3 equivalents of n- rrydroxy-uccinimide in dry ethyl acetate for 3 hours at room temperature. The reaction mixture was washed with 5 % HCl, dried over magnesium sulfate, filtered, and concentrated to a solid which was resuspended in DMSO ( 10 mg dye / 50 uL DMSO). The DMSO dye stock (5-10 μL) was added in excess (10-20 x) to an aminohexyl derivatized -21M13 oligonudeotide primer (lxlO '3 M) in 0.25 M bicarbonate carbonate buffer at pH 9.4 and allowed to react for 6 hours. The aminohexyl derivatized primer was prepared by automated solid-phase DNA synthesis using Aminolink-2 in the last cycle (PE p/n 400808). The dye labded oligonudeotide was separated from unreacted dye by passage through a Sephadex G-25 column duting with 0.1 molar triethylamine acetate (TEAA). The fraction containing the crude labded oligonucleotide was purified by reverse phase HPLC employing gradient elution from 8% AcCN in 0.1 M TEAA to 25% over 25 minutes using an RP-18 chromatography column. The pure dye labded oligonucleotide 13 was lyophilized to a solid and resuspended in 1 x TE buffer pH 8.4. The concentration of the dye labded oligonudeotide was determined by UV absoφtion at 260 nm assuming additive extinction coefficient values of 6,650 for T, 7,350 for C, 11,750 for G, and 14,900 for A, and the relative contribution of the dye absoφtion at 260 nm determined from spectra of the free dye measured in the same buffer. EXAMPLE 3 Comparison of the Excitation Spectra of TAMRA (22) and Cl-FLAN (2) Labeled Oligonucleotides from Example 2 Exdtation spectra were recorded for each dye in 1 x TBE buffer at pH 8.4. Dyes where present at an equimolar concentration (ca. 1 x IO "6 M). The emission intensity was recorded at λ nn xEm for each dye. FIG. 4 shows that for exdtation at 488 nm the relative exdtation efficiency of Cl-FLAN is approximately 2.5 times that of the TAMRA dye, while for exdtation at 514 nm, the relative exdtation effidency of Cl-FLAN is approximately 1.5 times that of the TAMRA dye. EXAMPLE 4 Comparison of the Quantum Yield of TAMRA (22) and Cl-FLAN (2) Labeled Oligonucleotides from Example 2 FIG. 5 shows emission spectra the fluorescense emission intensity of a TAMRA (22) labded -21M13 oligonudeotide and a CI-FLAN(2) labded -21M13 oligonucleotide exdted at the absoφtion maxima ofeach dye. The oligonucleotides were prepared as in Example 2. The data demonstrate a 60% greater quantum yield for the Cl-FLAN (2) labded oligonucleotide as compared to the TAMRA (22) labded oligonucleotide. Spectra were recorded in 1 x TE buffer at pH 8.4 at a concentration resulting in an equal λ«„Abs of 0.05 for each labded oligonudeotide. Emission spectra were recorded for each dye with irradiation at X^Abs for each dye. EXAMPLE 5 Comparison of the Molar Emission Intensity of Cl-FLAN (2) and TAMRA (22) Labeled Oligonucleotides Emission spectra of equimolar concentrations (ca. IxlO^M) of a TAMRA (22) labded oligonudeotide and a Cl-FLAN (2) labded oligonucleotide dissolved in 1 x TE buffer at pH 8.4 were measured by irradiating each oligonudeotide at 488 nm and 514 nm, and adding the spectra to approximate the radiation of a multiline argon laser. FIG. 6 shows that the fluorescence intensity of the Cl-FLAN (2) labded oligonudeotide is over 2 times greater than that of the TAMRA (22) labeled oligonucleotide. EXAMPLE 6 Multiplex Dye-labeled Oligonucleotide Set Long-wavdength fluorescence emission of a Cl-FLAN (2) labded oligonudeotide -21M13 sequencing primer was compared with the emission from -21M13 sequencing primers labded with 6-FAM, TET, and, HEX 23 dyes, where 6-FAM refers to 6-carboxyfluorescein, "TET' refers to ό-carboxy^ ^' '-tetrachlorofluorescein, and "HEX" refers to 6- carboxy-4,7,2',4',5',7'-hexachlorofluorescein. Primers were labeled as described above in Example 2. The exdtation wavdength was 490 nm. Emission spectra were run in 1 x TE buffer at pH 8.4 and normalized to equal intensity (ca. 1*10 " * M). FIG. 7 shows that the 573 nm emission maxima and the narrow width of the emission spectrum of the Cl-FLAN (2) labded oligonucleotide makes the Cl-FLAN (2) labded oligonudeotide spectrally resolved from the emission spectra of the other 3 dyes in the set. Such spectral resolution indicates the suitability of a dye set induding, FAM TET, and HEX labded oligonucleotides with the Cl-FLAN (2) asymmetric benzoxanthene dye. EXAMPLE Synthesis of a 2-Fluoro-l,3-Dihydroxynapthalene Intermediate See FIG. 8. Commercially available homopthallic anhydride (14) (100 gm) was reacted with ethanol (300 mL) under add catalysis (0.5 mL TFA) to produce a 95 % yidd of the intermediate ethyl ester 15 after refluxing for 3 hours, concentration to a solid, and recrystalization from toluene. Intermediate 15 (10 gm) was then reacted with 1.1 equivalents of oxalyl chloride in CH 2 CI 2 (200 mL) for 4 hours at room temperature to produce an 80% yidd of add chloride 16 as a crude solid after concentration at room temperature under high vacuum Crude 16 was suspended in THF and reacted by dther of the following two methods with fluoro acetate equivalents to produce compound 20. Method A: The potassium salt (17) of ethyl fluoroacetate (3 equivalents), formed by reaction of ethyl fluoroacetate and potassium t-butoxide at 0 °C in THF, or the magnesium salt of ethyl hydrogen fluoromalonate (18) (1.5 equivalents), formed by reaction of isopropyl magnesium bromide (2 equivalents) and ethyl hydrogen fluoromalonate at -60 °C, were added slowly to the THF suspension of 16 and allowed to react for 6 hours at 0 °C. The reaction was quenched by adding 5 % HCl, extracted (3 times) with EtOAc, the organic layer was dried, concentrated, and the resulting crude mixture purified by flash chromatography employing gradient dution from 6:4 hexanes/CH 2 Cl 2 to 100 % CH 2 C1 2 giving 35 to 50 % yidd of 5 compound 20. Method B: The phosphorous yiid 19 was slowly added to the THF suspension of 16 at - 70 °C, then allowed to warm to room temperature and react for 16 hours. The reaction was quenched by addition of 5 % NaHCOa and stirred for 6 hours. The reaction was extracted with 10 THF / water (3 times) and the product was isolated as for Method A to produce intermediate 20 in >50 % yidd. Purified 20 intra-molecularty cyclized under base catalysis (2 equivalents NaOEt) to a cyclic intermediate 21 which decarboxylated in situ to give the 2-fluoro-l,3- dihydroxynapthalene (9a) in 50% yidd. Alternatively, the cyclic intermediate 21 can be isolated in >80 % yidd when employing potassium t-butoxide in THF and decarboxylkated to 2-fluoro- 15 l,3-dihydroxynapthalene (9a). EXAMPLE S DNA Sequendng Employing Asymmetric Benzoxanthene Compound 2 20 Automated cycle sequencing was performed using a Perkin-Elmer Catalyst 800 Molecular Biology Labstation (The Perkin-Elmer Corporation, Foster City, CA (PE)). Four separate Sanger sequencing reactions were run employing the same -21 Ml 3 primer labded with 6-FAM (C terminator), TET (A terminator), HEX (G terminator), or Cl-FLAN 2 (T terminator) as described below. A mixture of the four reactions was loaded and data was 25 generated on a Perkin-Elmer ABI Prism™ 377 DNA sequencer and associated data analysis software. Cycle sequencing reactions were performed on the Catalyst 800 Molecular Biology Labstation using the 3.02 platform software. The Catalyst was programmed to deliver 0.6 μL of pGEM 3Z+ template DNA at a concentration of 100 ng/μL, and 1.9 μL of premix 30. defined below. Sequencing data was generated on an ABI Prism 1 * 4 377 DNA Sequencer using a 5% Long Ranger gel (FMC coφoration, Rockland, Maine). Each of the four sequencing premixes is defined below in Table I: TABLE I A Premix 60mM Tris pH 9.0; 2.5 mMMgC12; 4 mM Kcl; 0.04 mM DTT; 4 μMEDTA 0.1 μM TET labeled primer; 0.66U/μL Amplitaq FS; 1.66 U/μL rTth Pyrophosphatase; 0.5 μM ddATP; 125 μM dATP; 125 μM dCTP; 150 μM c7dGTP; 125 μM dTTP. C Premix 60mM Tris pH 9.0; 2.5 mM MgC12; 4 mM KCl; 0.04 mM DTT; 4 μM EDTA; 0.1 μM 6-FAM labeled primer; 0.66 U/μL Amplitaq FS; 1.66 U / μL rTth Pyrophosphatase; 0.5 μM ddCTP; 125 μM dATP; 125 μM dCTP; 150 μM c7dGTP; 125 μM dTTP. G Premix 60mM Tris pH 9.0; 2.5 mM MgCl 2 , 4 mM Kcl; 0.04 mM DTT; 4 μM EDTA 0.1 μM HEX labeled primer; 0.66U/μL Amplitaq FS; 1.66 U/μL rTth Pyrophosphatase; 0.375 μM ddGTP; 125 μM dATP; 125 μM dCTP; 150 μM c7dGTP; 125 μM dTTP. T Premix 60mM Tris pH 9.0; 2.5 mM MgC12; 4 mM Kcl; 0.04 mM DTT; 4 μM EDTA; 0.1 μM FLAN labeled primer; 0.66U/μL Amplitaq FS; 1.66 U/μL rTth Pyrophosphatase; 0.875 μM ddTTP; 125 μM dATP; 125 μM dCTP; 150μM c7dGTP; 125 μM dTTP. Cycle sequencing was performed on the above mixtures of template and premixes. The cycling conditions on the Catalyst were as follows: one cyde of 96 °C for 20 seconds; 15 cydes of 94 °C for 20 seconds, 55 °C for 40 seconds, and 68 °C for 60 seconds; and 15 cydes of 94 °C for 20 seconds and 68 °C for 60 seconds. Following thermal cycling, the four separate reactions were combined into the concentration buffer ( 83% DMSO/25mM EDTA/ 8mg/ml Blue Dextran ) and concentrated using standard Express Load methods (v 2.02 Catalyst Manual, PE). 2 mL of concentrated sample was loaded onto a well of the 377 sequencer, run, and analyzed using version 1.1 Software. The sequence between base 233 and 263 is shown in FIG. 9. EXAMPLE 9 Microsatellite Fragments Labeled using Cl-FLAN (2), HEX and TET Labeled Primers Separated Simultaneously with ROX Labeled Internal Size Standards. PCR reactions of four loci of a human CEPH family DNA using dye labded primers was performed as described bdow. The PCR products were pooled and electrophoretically separated on a Perkin-Elmer ABI Prism 377™ DNA sequencer (PE). The unique fluorescent signal of each dye labeled fragment peak was analyzed using GeneScan™ Analysis Software v 2.0.2 (PE). Referring to FIG. 10, the red peaks (labded R) correspond to ROX (26) labeled internal standard fragments, the blue peaks (labeled B) correspond to TET labeled fragments, the green peaks (labeled G) correspond to HEX labeled fragments, and the black peaks (labeled K) correspond to Cl-FLAN (2) labeled fragments. The PCR reactions were run on a Perkin-Elmer 9600 thermocycler (PE). A separate reaction was performed for each dye labeled primer employing the following cocktail: Reaction Comoonents Volume fuL) Dye labeled Primer Mix (5μM) 1.0 DNA (50 ng μL) 1.2 1 OX PE PCR Buffer π 1.5 dNTP mix (2.5 mM) 1.5 AmpliTaq* (5 units/μL) 0.12 2.0 mM MgCl 2 1.2 Sterile D.I. Water 8.48 Total Mix 15.0 The mixtures were amplified using the following cycling conditions: 1 cycle at 95 °C for 5 minutes; 10 cydes at 94 °C for 15 seconds, 55 °C for 15 seconds, and 72 °C for 30 seconds; 20 cycles at 89 °C for 15 seconds, 55 °C for 15 seconds, and 72 °C for 30 seconds; and 1 cycle at 72 °C for 10 minutes. The amplified PCR Products were pooled by mixing the Cl-FLAN (2) and TET - labeled PCR products (0.5 μL) with 1.0 μL ofeach HEX labeled PCR product to give an overall ratio of mixed dye labeled fragments consisting of 1:2:1 (Cl-FLAN : HEX : TET). The pooled PCR fragments were mixed with a loading cocktail consisting of 2.5 μL formamide, 0.5 μL Blue Dextran (50 mM EDTA, 50 mg/mL Blue Dextran), and 0.5 μL Size Standard (GS-350 ROX, PE p/n 401735). The pooled mixture was denatured at 95 °C for five minutes and then loaded onto one gel lane of a PE ABI Prism™ 377 DNA sequencer. The fragments were electrophoretically separated and detected using an acrylamide gel having the following characteristics: 0.20 mm thickness, 4.25% (wt) acrylamide, 19:1 acrylamide/bisacrylamide (wt/wt), 34-well square tooth comb, 10X TBE Buffer (89 mM Tris, 89 mM Boric Acid, 2 mM EDTA) pH of 8.3. The instrument was run using Filter Wheel A and the GS 36D-2400 Module which has the following run parameters: EP Voltage of 3000 V, EP Current of 60.0 mA, EP Power of 200 W, Gel Temperature of 51 °C and a laser power of 40 mW. EXAMPLE 10 Comparison of the Spectral Properties, Photostability, and Chemical Stability of Rhodamine Dyes, Xanthene Dyes and the Asymmetric Xanthene Dyes of the Invention Table I below summarizes and compares various spectral and chemical properties of the asymmetric benzoxanthene dyes of the invention and other spectrally similar xanthene and rhodamine-based dyes. TABLE π See FIGS. 1 and 2 for the structures of the dyes referred to in the table. All data are reported for pure dye isomer 2. All emission spectra were recorded in 1 x TBE buffer at pH 8.4 in dye solutions having an absorbance of 0.05 at λ„ « Abs (ca. 1 x IO "6 M) at room temperature. Photodecomposition rate was determined for equal volumes of the dyes at initially 1 absoφtion unit at λ π ^Abs and run in pairs at equal volumes under equal high intensity white light irradiation at 35 °C in 1 x TBE buffer pH 8.4. Absoφtion spectra of aliquots were taken at 1 hour intervals and the intensities at X^Em were fitted with first order exponential curves to determine the n rate for loss of dye. Relative brightness at aixEm was determined using 514 nm exdtation of dyes at approximately equal concentrations. (λ««Abs= 0.05). For the NFUOH stability measurements the dyes were diluted in concentrated ammonia hydroxide at approximately equal concentrations (λ- n „Abs = 1) and incubated at 60 °C for 20 hours in sealed vials. Absoφtion spectra of aliquots were taken at 1 hour intervals and the intensities at λmxEm were fitted with first order exponential curves to determine the Un for dye decomposition. All publications and patent applications are herein incoφorated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incoφorated by reference. Those having ordinary skill in the chemical and biochemical arts will clearly understand that many modifications are possible in the preferred embodiment without departing from the teachings thereof. All such modifications are intended to be encompassed within the following claims.

Claims: WE CLAIM: 1. An asymmetric benzoxanthene dye compound having the formula: 5 wherein: Yi and Y 2 taken separatdy are selected from the group consisting of hydroxyl, oxygen, imminium, and amine; Ri-Rβ taken separatdy are selected from the group consisting of hydrogen, fluorine, chlorine, lower alkyl, lower alkene, lower alkyne, sulfonate, sulfone, amino, imminium, amido, 10 nitrile, lower alkoxy, linking group, and combinations thereof; and R is sdected from the group consisting of acetylene, lower alkyl, lower alkene, cyano, phenyl, substituted phenyl, heterocyclic aromatic, and combinations thereof, the substituted phenyl having the structure: 15 wherein: X1-X5 taken separately are hydrogen, chlorine, fluorine, lower alkyl, carboxyiic add, sulfonic add, -CH^H, or linking group. 2. The compound of claim 1 wherein one of Yi and Y 2 is oxygen and the other is 20. hydroxyl. 3. The compound of claim 1 wherein: Xi is selected from the group consisting of carboxyiic add, sulfonic add, and -CH 2 OH X 2 and Xj taken separatdy are sdected from the group consisting of hydrogen, chlorine, fluorine, and lower alkyl; and X 3 and X taken separately are selected from the group consisting of hydrogen, chlorine, fluorine, lower alkyl, carboxyiic add, sulfonic add, and linking group. 4. The compound of claim 1 wherein X 2 and Xs are chlorine. 5. The compound of claim 1 wherein Xi is carboxyiic add. 6. The compound of claim 1 wherein one of X 3 or t is linking group, the other being hydrogen. 7. The compound of claim 1 wherein one of Xi or Xs is sdected from the group consisting of carboxyiic add, sulfonic add, and -CH 2 OH. 8. The compound of claim 1 wherein one of Rι-R 3 is fluorine. 9. The compound of daim 8 wherein R 3 is fluorine. 10. The compound of claim 1 wherein: one of Yi and Y 2 is oxygen and the other is hydroxyl; Ri is a chlorine; j is a fluorine; R 2 and R*-Rg are hydrogen; and Rβ is substituted phenyl wherein Xi is carboxyl, X 2 and X 5 are chlorine, and one of X 3 and XA is carboxyl and the other is hydrogen. 11. The compound of claim 1 wherein: one of Yi and Y 2 is oxygen and the other is hydroxyl; Ri and R are fluorine; R 2 , and R -Rβ are hydrogen; and Rβ is substituted phenyl wherein Xi is carboxyl, X 2 and Xs are chlorine, and one of X 3 and X 4 is carboxyl and the other is hydrogen. 12. The compound of claim 1 wherein: one of Yi and Y 2 is oxygen and the other is hydroxyl; Ri is methoxy, R 2 is chlorine, Rs is fluorine; Ri-Rg are hydrogen; and Rp is substituted phenyl wherein Xi is carboxyl, X 2 and X are chlorine, and one of X 3 and X» is carboxyl and the other is hydrogen. 13. The compound of claim 1 wherein: one of Yi and Y 2 is oxygen and the other is hydroxyl; Rj is fluorine; Ri, R., and R«-R» are hydrogen; and R is substituted phenyl wherein Xi is carboxyl, X 2 and X 5 are chlorine, and one of X 3 and X4 is carboxyl and the other is hydrogen. 14. The compound of claim 1 wherein: one of Yi and Y 2 is oxygen and the other is hydroxyl; Ri-Rβ are hydrogen; and Rβ is substituted phenyl wherein Xi is carboxyl, X 2 and X 5 are chlorine, and one of X 3 and 4 is carboxyl and the other is hydrogen. 15. The compound of claim 1 wherein: one of Yi and Y 2 is oxygen and the other is hydroxyl; Ri is chlorine; R ∑ -Rβ are hydrogen; and Rβ is substituted phenyl wherein Xi is carboxyl, X 2 and X } are chlorine, and one of X 3 and X4 is carboxyl and the other is hydrogen. 16. The compound of claim 1 wherein: one of Yi and Y 2 is oxygen and the other is hydroxyl; Ri is methoxy; R 2 is chlorine; Rj-Rβ are hydrogen; and R is substituted phenyl wherein Xi is carboxyl, X 2 and Xs are chlorine, and one of X 3 and X is carboxyl and the other is hydrogen. 17. A phosphoramidite compound having the formula: wherein: X is a spacer arm; Y is a linkage; Bj is a phosphite ester protecting group; B 2 , and B 3 taken separately are sdected from the group consisting of lower alkyl, lower alkene, aryl, and cycloalkyl containing up to 10 carbon atoms; and D is the dye compound of Claim 1 ; wherein Y and D are linked through a linkage attached to dye D at one of positions Ri- R* . 18. The compound of claim 17 wherein B 2 and B 3 taken together form an alkene chain containing up to 5 carbon atoms in the prindple chain and a total of up to 10 carbon atoms with both terminal valence bonds of said chains being attached to the nitrogen atom; or B 2 and B 3 taken together with the nitrogen atom form a saturated nitrogen heterocycle which contains one or more heteroatoms sdected from the group consisting of nitrogen, oxygen, and sulfur. 19. The compound of claim 18 wherein: Bi is sdected from the group consisting of methyl, β-cyanoethyl, or 4-nitrophenylethyl; B 2 and B 3 taken separately are sdected from the group consisting of isopropyl, t-butyl, isobutyl, and sec-butyl; and B 2 and B 3 taken together is moφholino. 20. The compound of claim 17 wherein X and Y taken together is wherein n ranges from 2 to 10. 21. The compound of claim 17 wherein X and Y taken together is O II (CH 2 CH 2 O)n— CH 2 CH 2 -NH— C — wherein n ranges from 2 to 10. 22. A phosphoramidite compound having the formula: wherein: Bi is a phosphite ester protecting group; B 2 , and B 3 taken separatdy are sdected from the group consisting of lower alkyl, lower alkene, aryl, and cydoalkyl containing up to 10 carbon atoms; Bs is an add-cleavable hydroxyl protecting group; B is a nudeotide base; and D is the dye compound of Claim 1 ; wherein when B is purine or 7-deazapurine, the sugar moiety is attached at the Im¬ position of the purine or 7-deazapurine, and when B is pyrimidine, the sugar moiety is attached at the N'-position of the pyrimidine; wherein B and D are linked through a linkage attached to D at one of positions R 1 -R 9 ; and wherein if B is a purine, the linkage is attached to the 8-position of the purine, if B is 7- deazapurine, the linkage is attached to the 7-position of the 7-deazapurine, and if B is pyrimidine, the linkage is attached to the 5-position of the pyrimidine. 23. The compound of claim 22 wherein the linkage is O II 2 -NH-C — 24. The compound of claim 22 wherein the linkage is O O II II :≡C— CH 2 -NH— C— (CH 2 ) 5 -NH— C- 25. The compound of claim 22 wherein the linkage is O O II II -NH— (CH 2 ) 5 -NH— C- 26. The compound of claim 22 wherein B is sdected from the group consisting of uracil, cytosine, deazaadenine, and deazaguanosine. 27. A compound having the formula: wherein: R3-R7 taken separately are sdected from the group consisting of hydrogen, fluorine, chlorine, lower alkyl, lower alkene, lower alkyne, sulfonate, ammo, amido, nitrile, lower alkoxy, and linking group; and Y 2 is sleeted from the group consisting of hydroxyl and amine. 28. The compound of daim 27 wherein R 3 is fluorine. 29. The compound of claim 27 wherein Y 2 is hydroxyl. 30. A labeled nucleotide having the formula: wherein: B is a 7-deazapurine, purine, or pyrimidine nucleotide base; Wi and W 2 taken separately are selected from the group consisting of H and OH; W 3 is seleαed from the group consisting of OH, O O O O O O II II II II II II — O— P— O — O— P— O— P— O — O— P— O— P— O— P— O O O O O O O and D is the dye compound of Claim 1; wherein when B is purine or 7-deazapurine, the sugar moiety is attached at the Im¬ position of the purine or deazapurine, and when B is pyrimidine, the sugar moiety is attached at the N'-posrtion of the pyrimidine; wherein the linkage linking B and D is attached to D at one of positions R 1 -R 9 ; and wherein if B is a purine, the linkage is attached to the 8-position of the purine, if B is 7- deazapurine, the linkage is attached to the 7-position of the 7-deazapurine, and if B is pyrimidine, the linkage is attached to the 5-position of the pyrimidine. 31. The labded nucleotide of claim 30 wherein B is sdected from the group consisting of uracil, cytosine, deazaadenine, and deazaguanosine. 32. The labeled nudeotide of claim 30 wherein the linkage is O II — CssC— CH 2 -NH— C — 33. The labded nucleotide ofclaim 30 wherein both Wi and W 2 are H; and W 3 is 34. The labded nudeotide of claim 30 wherein W ( is H; W 2 is OH; and W 3 is 35. A labded polynucleotide containing a nudeotide having the formula: wherein: B is a 7-deazapurine, purine, or pyrimidine nucleotide base; Zi is selected from the group consisting of H and OH; Z 2 is selected from the group consisting of H, OH, HPO , and Nuc, wherein Nuc and the nucleoside are linked by a phosphodiester linkage, the linkage being attached to the 5 '-position of Nuc; Z 3 is selected from the group consisting of H, HPO 3 , phosphate analogs, and Nuc, wherein Nuc and the nucleoside are linked by a phosphodiester linkage, the linkage being attached to the 3 '-position of Nuc; and, D is a dye compound of Claim 1 ; wherein when B is purine or 7-deazapurine, the sugar moiety is attached at the Im¬ position of the purine or deazapurine, and when B is pyrimidine, the sugar moiety is attached at the N'-position of the pyrimidine; wherein the linkage linking B and D is attached to D at one of positions Ri-Rβ ; and wherein if B is a purine, the linkage is attached to the 8-posmon of the purine, if B is 7- deazapurine, the linkage is attached to the 7-position of the 7-deazapurine, and if B is pyrimidine, the linkage is attached to the 5-position of the pyrimidine. 36. The labeled polynucleotide of claim 35 wherein B is sdected from the group consisting of uracil, cytosine, deazaadenine, and deazaguanosine. 37. The labded polynucleotide of claim 35 wherein the linkage is O _ ll__ 38. A method of polynucleotide sequencing comprising the steps of: forming a mixture of a first, a second, a third, and a forth class of porynucleotides such that: each polynudeotide in the first class indudes a 3 '-terminal dideoxyadenosine and is labeled with a first dye; each polynucleotide in the second dass includes a 3 '-terminal dideoxycytidine and is labeled with a second dye; each polynucleotide in the third class includes a 3 '-terminal dideoxyguanosine and is labeled with a third dye; and each polynudeotide in the forth class indudes a 3 '-terminal dideoxythymidine and is labded with a forth dye; wherein one of the first, second, third, or forth dyes is the asymmetric benzoxanthene dye of Claim 1; the other of the dyes being spectrally resolvable from the asymmetric benzoxanthene dye and from each other, electrophoretically separating the polynudeotides thereby forming bands of similariy sized polynucleotides; illuminating the bands with an illumination beam capable of causing the dyes to fluoresce; and identifying the classes of the polynudeotides in the bands by the fluorescence spectrum of the dyes. 39. The method of claim 38 wherein the other of the dyes are sdected from the group consisting of 6-carboxyfluorescein, 6-carboxy-4,7,2\7'-tetrachlorofluorescein, and 6-carboxy- 4,7,2',4\5\7'-hexachlorofluorescein. 40. A method of fragment analysis comprising: forming a labeled polynucleotide fragment, the fragment being labded with the dye compound of Claim 1; subjecting the labded polynudeotide fragment to a size-dependent separation process; and detecting the labeled polynucleotide fragment subsequent to the separation process. 41. The method of claim 40 wherein the size-dependent separation process is dectrophoresis and the detecting is by fluorescence.

Inventors: BENSON SCOTT C, FURNISS VERGINE C, HAUSER JOAN, HENNESSEY KEVIN M, MENCHEN STEVEN M, THEISEN PETER D, BENSON, SCOTT, C., FURNISS, VERGINE, C., HAUSER, JOAN, HENNESSEY, KEVIN, M., MENCHEN, STEVEN, M., THEISEN, PETER, D.
Applicants: PERKIN ELMER CORP, THE PERKIN-ELMER CORPORATION
Application year: 1997
Main classification: C09B11
IPC codes: C07C39, C07D311, C07F9, C07H19, C07H21, C09B11, C09K11, C12N15, C12Q1, G01N33