Abstract:
The invention is directed to a method of incorporating expanded porphyrins, and particularly of incorporating a sapphyrin or a texaphyrin, before, during, or after chemical synthesis of an oligomer to form an expanded porphyrin-oligonucleotide conjugate, and particularly a sapphyrin- or texaphyrin-oligonucleotide conjugate. This method includes reacting derivatized nucleotides and a sapphyrin or a texaphyrin in a desired order in an automated or manual DNA synthesizer having a solid support to form a sapphyrin- or a texaphyrin-oligonucleotide conjugate.

Description:
This application is a continuation-in-part application of U.S. Ser. No. 08/310,501, filed Sep. 21, 1994, which is a continuation-in-part application of U.S. Ser. No. 08/112,872 filed Aug. 25, 1993, now U.S. Pat. No. 5,491,576, and of International application No. PCT/US94/06284 designating the United States and filed Jun. 9, 1994. U.S. Ser. No. 08/112,872 is a divisional application of U.S. Ser. No. 07/822,964 filed Jan. 21, 1992, now U.S. Pat. No. 5,252,720. PCT/US94/06284 is a continuation-in-part application of U.S. Ser. No. 08/227,370 filed Apr. 14, 1994, which is a continuation-in-part application of U.S. Ser. No. 08/075,123 filed Jun. 9, 1993, now abandoned, which is a continuation-in-part of U.S. Ser. No. 07/822,964 filed Jan. 21, 1992, now U.S. Pat. No. 5,252,720. All of the above-named patents are incorporated by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to a method of step-wise synthesis of conjugates of expanded porphyrins and oligonucleotides. 
     BACKGROUND OF THE INVENTION 
     &#34;Expanded porphyrins&#34; are large, pyrrole-containing macrocyclic analogues of the porphyrins. Examples of these compounds are porphine, the smaragdyrins, sapphyrins, oxosapphyrins, platyrins, pentaphyrins, hexaphyrins, superphthalocyanines, rubyrins, and texaphyrins. Such molecules are of potential interest because suitably designed systems could act as versatile ligands capable of binding larger metal cations and/or stabilizing higher coordination geometries than those routinely accommodated within the normally tetradentate ca. 2.0 Å radius porphyrin core. The resulting complexes could have important application in the area of heavy metal chelation therapy, serve as contrast agents for magnetic resonance imaging (MRI) applications, act as vehicles for radioimmunological labeling work, or serve as useful photosensitizers for photodynamic therapeutic applications. 
     The texaphyrins have been found to be useful as MRI contrast agents, as radiation sensitizers and in photodynamic therapy (PDT), as well as having the ability to hydrolytically cleave phosphate esters, including RNA, and to photolytically cleave RNA and DNA. Texaphyrin is considered as being an aromatic benzannulene containing both 18π- and 22π-electron delocalization pathways. See, e.g., Sessler, J. L. et al., Accounts of Chemical Research, 1994, 27, 43. Texaphyrins and water-soluble texaphyrins and method of preparation have been described in U.S. Pat. Nos. 4,935,498; 5,252,720; 5,256,399; 5,272,142; and 5,292,414; and in International publn.s WO 94/29316 and WO 95/01996; all of which are incorporated herein by reference. 
     Sapphyrins and water-soluble sapphyrins and methods of preparation having been described in U.S. Pat. Nos. 5,041,078; 5,120,411; 5,159,065; and 5,302,715; and in International publn. WO 94/09994; all of which are incorporated herein by reference. Rubyrins are described in U.S. Pat. No. 5,410,045, incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a method of incorporating expanded porphyrins, and particularly of incorporating a sapphyrin or a texaphyrin before, during, or after chemical synthesis of an oligomer to form a sapphyrin- or texaphyrin-oligonucleotide conjugate. This method comprises the steps of obtaining an automated or manual DNA synthesizer having a solid support. Further steps include reacting derivatized oligonucleotides and an expanded porphyrin, particularly a sapphyrin or a texaphyrin, in a desired order to form a sapphyrin- or a texaphyrin-oligonucleotide conjugate. For example, an oligonucleotide may be formed by repeated steps of reacting nucleotides on the solid support. Sapphyrin or texaphyrin may be coupled in the final step to form a conjugate with a 5&#39; linkage. Alternatively, a sapphyrin or texaphyrin may be coupled to the solid support followed by the addition of nucleotides to form a conjugate with a 3&#39; linkage. A third possibility is the coupling of nucleotides followed by a macrocycle, such as texaphyrin or sapphyrin, then followed by nucleotides to form a conjugate where an internal residue is a macrocycle. 
     The oligonucleotide may be linked to the sapphyrin or texaphyrin in a 3&#39; linkage, a 5&#39; linkage, or a linkage internal to the oligonucleotide. The texaphyrin or sapphyrin may be coupled as a phosphoramidite, H-phosphonate, or phosphate triester derivative and may be coupled to the growing end of the oligonucleotide in the synthesizer during or in the final step of synthesis. 
     Following long-standing patent law convention, the terms &#34;a&#34; and &#34;an&#34; mean &#34;one or more&#34; when used in this application, including the claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein. 
     FIGS. 1A, 1B, 1C, 1D, 1E, 1F and FIG. 1G show stepwise synthesis schemes for preparing texaphyrin metal complex-oligonucleotide conjugates and sapphyrin oligonucleotide conjugates. FIG. 1A shows the synthesis of a texaphyrin metal complex 3&#39;-linked-oligonucleotide conjugate. FIG. 1B and FIG. 1C show an approach that results in a 5&#39;-linked oligonucleotide conjugate. FIG. 1D shows the synthesis of a 5&#39;-linked sapphyrin-oligonucleotide conjugate. FIG. 1E shows the synthesis of a precursor sapphyrin that may be linked to two oligonucleotides. FIG. 1F and FIG. 1G show the synthesis of a sapphyrin oligonucleotide conjugate via the H-phosphonate method. Example 1 provides the details of these stepwise synthesis schemes. In FIGS. 1A-1C, M is H, a divalent metal cation or a trivalent metal cation; and N +  will typically be an integer less than or equal to 5. In the context of the basic macrocycle with a divalent or trivalent metal cation, N +  is 1 or 2; however, the complexes may have one or more additional ligands providing charge neutralization and/or coordinative saturation to the metal ion. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention provides synthetic procedures in which an expanded porphyrin, and in particular a texaphyrin or a sapphyrin, is inserted directly into a nucleic acid synthesis scheme, preferably on a solid support. Texaphyrin and sapphyrin macrocycles were not known to be stable under the basic conditions employed in the synthesis of oligonucleotides. For example, until the results presented herein were obtained, it was thought that texaphyrin, being a Schiff base, may be unstable to the basic conditions employed during oligonucleotide synthesis, specifically during the ammonia and ethanol cleavage and deprotection steps. It was also possible that the meso positions of sapphyrin would be unstable to the same basic conditions. Therefore, the stepwise synthesis of texaphyrin- and sapphyrin-oligonucleotide conjugates presented herein was a surprising and unexpected result. The synthesis of sapphyrin-nucleobase conjugates is described in U.S. Ser. No. 07/964,607, and U.S. Pat. No. 5,457,195, and International publn. WO 94/09003, incorporated by reference herein. 
     It is contemplated that the stepwise synthesis provided herein may be performed manually or may be automated, and may be in a solution-phase or on a solid support. Solid support synthesis may be accomplished using an automated or a manual nucleic acid synthesizer. Common solid supports are CPG (control pore glass) and CPS (control pore silica). Other possible solid supports include polystyrene, polyamide/Kieselguhr, and cellulose paper. A preferred embodiment of this method is automated synthesis on a solid support. 
     Attachment of a texaphyrin or sapphyrin to an oligonucleotide during stepwise synthesis obviates the need for a postmodification protocol and a second purification of the product. This results in an improved yield and greatly facilitates scale-up. The texaphyrin may be a free base texaphyrin or may be a texaphyrin metal complex. 
     Oligomeric DNA, up to ca 100 residues in length, can be prepared on a commercial synthesizer, such as for example Applied Biosystems Inc. model 392. Most commercial synthesizers employ phosphoramidite chemistry. In brief, DNA is synthesized from the 3&#39; to the 5&#39; direction through the sequential addition of highly reactive phosphorus(III) reagents called phosphoramidites. The initial 3&#39; residue is covalently attached to a controlled porosity silica solid support, which greatly facilitates manipulation of the polymer. After each residue is coupled to the growing polymer chain, the phosphorus(III) is oxidized to the more stable phosphorus(V) state by a short treatment with iodine solution. Unreacted residues are capped with acetic anhydride, the 5&#39;-protective groups is removed with weak acid, and the cycle may be repeated to add another residue. The full-length polymer is released from the solid support, with concommitant removal of remaining protective groups, by exposure to base: A common protocol uses saturated ethanolic ammonia. 
     The finding that lanthanide(III) metal complexes of texaphyrins, notably DyT2B2 (cpd. 1 A , M=Dy) and EuT2B1 (cpd. 1 B , M=Eu), are stable to treatment with ethanolic ammonia for 24 h at ambient temperature suggests that it is possible to derivatize oligomers with lanthanide(III) texaphyrin complexes during stepwise synthesis to produce texaphyrin-oligonucleotide conjugates, such as for example cpd. 1 c . ##STR1## 
     A texaphyrin or metal complex thereof or a sapphyrin molecule may be inserted into the synthesis scheme of an oligonucleotide in a variety of ways. Possible linkages include amide, phosphate, thioether, amino, and ether linkages. An amide linkage represents the reaction of an activated carboxylic acid derivative of a macrocycle (such as cpd. 1 B ) and an amino linker attached to an oligonucleotide. Activation may be achieved in solution phase or on a solid support using DCC and NHS, EDC, or activated esters of NHS, nitrophenyl, pentachlorophenyl, acid anhydride, or sulfonyl chloride. In addition, for the solid support reaction, activation may be in the form of an acid chloride. A phosphate linkage represents the reaction of an activated phosphate derivative of a macrocycle and the 5&#39; hydroxyl group on an oligonucleotide. The activated phosphate may be a phosphoramidite, an H-phosphonate, a triester, or a diester. 
     The terms &#34;expanded porphyrin-oligonucleotide conjugate&#34;, &#34;sapphyrin-oligonucleotide conjugate&#34; and &#34;texaphyrin-oligonucleotide conjugate&#34; mean that a nucleotide or an oligonucleotide is attached to the expanded porphyrin, sapphyrin or texaphyrin, respectively, in a 5&#39; or a 3&#39; linkage, or in both types of linkages to allow the macrocycle to be an internal residue in the conjugate. It can also refer to an expanded porphyrin, a sapphyrin or a texaphyrin, respectively, that is linked to an internal base of the nucleotide or oligonucleotide. The nucleotide or oligonucleotide may be attached either directly to the expanded porphyrin, sapphyrin or texaphyrin or to the macrocycle via a linker or a couple of variable length. 
     It is understood that the terms &#34;nucleotide&#34;, &#34;polynucleotide&#34; and &#34;oligonucleotide&#34;, as used herein and in the appended claims, refer to both naturally-occurring and synthetic nucleotides, poly- and oligonucleotides and to analogs and derivatives thereof such as methylphosphonates, phosphotriesters, phosphorothioates and phosphoramidates and the like. Deoxyribonucleotides, deoxyribonucleotide analogs and ribonucleotide analogs are contemplated as being useful in the present invention. 
     The nucleotides or oligonucleotides may be derivatized at the bases, the sugars, the ends of the chains, or at the phosphate groups of the backbone to promote in vivo stability. Modifications of the phosphate groups are preferred in one embodiment since phosphate linkages are sensitive to nuclease activity. Presently preferred oligonucleotide derivatives are the methylphosphonates, phosphotriesters, phosphorothioates, and phosphoramidates. Additionally, the phosphate linkages may be completely substituted with non-phosphate linkages such as amide linkages. Appendages to the ends of the oligonucleotide chains also provide exonuclease resistance. Sugar modifications may include groups, such as halo, algol, alkenyl or alkoxy groups, attached to an oxygen of a ribose moiety in a ribonucleotide. In a preferred embodiment, the group will be attached to the 2&#39; oxygen of the ribose. In particular, halogen moieties such as fluoro may be used. The alkoxy group may be methoxy, ethoxy or propoxy. The alkenyl group is preferably allyl. The alkyl group is preferably a methyl group and the methyl group is attached to the 2&#39; oxygen of the ribose. Other alkyl groups may be ethyl or propyl. 
     Representatives of texaphyrins which may be activated and attached to nucleotides following the present invention are included within the following structure I: ##STR2## wherein, M is H, a divalent metal cation or a trivalent metal cation; R 1  -R 4 , R 7  and R 8  are independently hydrogen, halide, hydroxyl, alkyl, aryl, haloalkyl, nitro, formyl, acyl, hydroxyalkyl, oxyalkyl, oxyhydroxyalkyl, saccharide, carboxy, carboxyalkyl, carboxyamide, carboxyamidealkyl, aminoalkyl, sulfonatoalkyl, amidealkyl, or aryl; R 6  and R 9  are independently selected from the groups of R 1  -R 4 , R 7  and R 8 , with the proviso that the halide is other than iodide and the haloalkyl is other than iodoalkyl; R 5  and R 10  -R 12  are independently hydrogen, alkyl, aryl, hydroxyalkyl, oxyalkyl, oxyhydroxyalkyl, carboxyalkyl, or carboxyamidealkyl; and Z will typically be an integer less than or equal to 5. 
     Representatives of sapphyrins which may be activated and attached to nucleotides following the present invention are disclosed in International publn. WO 94/09003, the disclosure of which is incorporated herein by reference. 
     The following example discusses four representative synthetic schemes. 
     EXAMPLE 1 
     Stepwise Synthesis of Texaphyrin- and Sapphyrin-Oligonucleotide Conjugates 
     In the approach depicted in FIG. 1A, a metal-texaphyrin (&#34;txp&#34;) complex 7A 2  is attached to a solid support 7A 1  via a six-carbon amine linker. This amide-forming coupling reaction is currently employed to attach the complex post-synthetically. It is important to note that texaphyrin hydroxyl groups are protected as an ester on 7A 3  for stepwise synthesis. These protecting groups are labile to the ethanolic ammonia treatment. Such a metal-txp-derivatized support may be used for stepwise synthesis, and upon cleavage and deprotection, results in a 3&#39;-linked metal-txp-DNA conjugate 7A 4 . The amide-forming reaction may also occur at the conclusion of DNA synthesis before deprotection and cleavage from the solid support. 
     As depicted in FIG. 1B, a phosphoramidite derivative of a metal texaphyrin complex 7B 2  is prepared by reaction of the monoalcohol 7B 1  with phosphitylating agent and diisopropylethylamine. The hydroxyl groups are again protected as the ester for this synthesis. The resulting phosphoramidite is coupled on the synthesizer as the final residue to form 7B 3 . In this approach, deprotection results in a 5&#39;-linked txp-metal complex-DNA conjugate 7C 2 . This txp-conjugate has no amide bonds in the linker. 
     A txp-DNA conjugate having the texaphyrin in an internal linkage to the oligonucleotide may be synthesized using this stepwise approach. A dihydroxytexaphyrin is treated with dimethoxytrityl chloride in the presence of dimethylaminopyridine and pyridine. The resulting monoprotected texaphyrin is treated with phosphitylating agent and diisopropylethylamine to produce a monoprotected phosphoramidite. This product is coupled to a growing oligonucleotide during synthesis in place of a nucleotide residue to insert a texaphyrin in an internal linkage. The monoconjugate may then be further coupled to nucleotides to produce a txp-DNA conjugate having the texaphyrin in an internal linkage to the oligonucleotide. Additionally, phosphonate or phosphodiester derivatives of texaphyrin may be utilized to form similar internal, 3&#39;, or 5&#39; linkages by the phosphonate or triester methods, respectively. 
     Oligonucleotide analog conjugates may be coupled to texaphyrins in a similar manner as herein described. In particular, phosphorothioates, 2&#39;-O-methylated ribonucleotides, or other nucleic acid analogs such as methyl phosphonate derivatives are preferred due to the enhanced stability the derivatization provides towards nucleases in vivo. 
     Other macrocycles may be coupled to oligomers to form Z0 macrocycle-nucleic acid conjugates in a similar manner. For example, sapphyrin-oligonucleotide conjugates have been made using a direct coupling amide linkage method or by incorporation during oligonucleotide synthesis forming a 5&#39; linkage via the H-phosphonate method as follows. 
     Direct coupling method (amide linkage): Sapphyrin-oligonucleotide conjugates with an amide linkage were formed on a solid support (FIG. 1D). Specifically, sapphyrin monoacid 7D 1  (6.8 mg, 0.011 mmol, 50 eq) was dissolved in 2 mL of methylene chloride in a 4 mL glass vial with a small stirbar followed by cooling to 0° C. with an ice batch. Dicyclohexylcarbodiimide (4.5 mg, 0.022 mmol, 100 eq), dimethylaminopyridine (0.001 mg, catalytic amount), and N-hydroxysuccinimide (2.5 mg, 0.022 eq, 100 eq) were added to the solution which was then stirred for 30 min. Protected amino-derivatized oligonucleotide attached to CPG solid support (7D 2  2.5 mg, 0.108 μMol, 1 eq) was added to the solution which was stirred overnight at room temperature. The solution was filtered, and the conjugate attached to the CPG (7D 3 ) was washed once with methylene chloride and twice with methanol. The green solids were then suspended in conc. ammonium hydroxide for 4 h at room temperature after which the green solution was filtered and evaporated to afford the crude sapphyrin-oligonucleotide conjugate 7D 4 . The conjugate 7D 4  could be purified by fplc on a C 18  column using acetonitrile/100 mM triethylammonium acetate, pH 7.0. 
     This method is similar to that described to form texaphyrin-oligonucleotide conjugates. The coupling step in this case was done on a solid support although it may be done in solution. This procedure attaches sapphyrin to the 5&#39; end of the oligonucleotide and could be modified to link macrocycles to the 3&#39; end, or internal to an oligonucleotide. 
     Incorporation during oligonucleotide synthesis (phosphate linkage): The monoprotected sapphyrin H-phosphonate 7F 2  (7E 3 ) was synthesized for incorporation during oligonucleotide synthesis (FIG. 1E). A sapphyrin-conjugate 7G 1  was synthesized in a solid-phase manual oligonucleotide synthesizer via the H-phosphonate method (FIG. 1F and FIG. 1G). The oligonucleotide was assembled on a solid support such as controlled pore glass (CPG) by a cycle of steps. The 5&#39; end of the growing oligonucleotide was deprotected, the reaction phase was neutralized, and the activated monoprotected nucleotide H-phosphonate was coupled at the 5&#39; end of the oligonucleotide. Derivatized sapphyrin 7F 2  (7E 3 ) was incorporated at the 5&#39; end of the oligonucleotide 7F 1  during the last step of the synthesis in place of a nucleotide (FIG. 1F). 
     Specifically, the desired oligonucleotide was synthesized on a CPG solid support on a 0.2 μM scale. The derivatized sapphyrin 7F 2  (7E 3 ) was attached to the oligonucleotide 7F 1  on a manual oligonucleotide synthesizer (Cruachem PS 150 DNA Synthesizer, Sterling, Va.). The synthesis was run under argon (5 psi). Syringes were oven-dried and kept in a desiccator until use. The following sequence was used for coupling: 
     1. Wash--acetonitrile--2 min. 
     2. Deblock--3% dichloroacetic acid in methylene chloride--3 min. 
     3. Wash--acetonitrile--2 min. 
     4. Wash--acetonitrile/pyridine (1:1)--2 min. 
     5. Couple--4 mM derivatized sapphyrin 7F 2  (7E 3 ) (1 eq) in methylene chloride and 65 mM pivaloyl chloride in acetonitrile/methylene chloride (1:1)--30 μL solution alternating for 1.5 min. 
     6. Wait--15 min. 
     7. Wash--acetonitrile, acetonitrile/pyridine (1:1), acetonitrile--2 min, 1 min, 2 min. 
     8. Deprotect--3% dichloroacetic acid in methylene chloride--3 min. 
     9. Wash--acetonitrile, acetonitrile/pyridine (1:1)--2 min, 2 min. 
     10. Oxidize--0.1M iodine in water/pyridine/N-methylimidazole/THF (5/4/1/90), 0.1M iodine in water/triethylamine/THF (5/5/90)--2 min, 2 min. 
     11. Wash--acetonitrile/pyridine (1:1), acetonitrile, methanol--2 min, 1 min, 2 min. 
     The conjugate 7F 3  attached to CPG was added to 2 mL conc. ammonium hydroxide for 4 h. The solution was filtered and the filtrate was evaporated to afford crude sapphyrin-oligonucleotide conjugate 7G 1  which could be purified by fplc on a C 18  column using acetonitrile/100 mM triethylammonium acetate pH 7.0. 
     This method may be used to synthesize any type or length of oligonucleotide with macrocycle modifications at the 5&#39; end or in the interior of the oligonucleotide. Additionally, the oligonucleotide could be modified with multiple macrocycles. 
     A further method for the synthesis of macrocycle-oligonucleotide conjugates is to incorporate nucleotides enzymatically. A variety of DNA and RNA polymerases may be used; however, the Klenow fragment of DNA polymerase I from E. coli and terminal deoxynucleotidyl transferase are preferred. Goodchild, J. (1990) provides a general discussion of the enzymatic synthesis of oligonucleotides and is incorporated by reference herein. 
     EXAMPLE 2 
     Preparation of a Texaphyrin Phosphoramidite 
     A texaphyrin phosphoramidite compound for use in coupling to a nucleotide according to the method of the present invention was prepared as follows. 
     1,2-Dinitro-4-hydroxy-5-methoxybenzene. Dinitroveratrole (5 g, 0.0219 mol) was dissolved in glacial acetic acid (50 mL), and concentrated HBr (48% w/w in water, 165 mL) was added all at once at room temperature (RT). The reaction temperature was elevated to 110° C., and the system was stirred for 6 h. After cooling to RT, ice-water (150 mL) was added and a mixture of starting material and target was extracted from the aqueous phase using chloroform (2×400 mL). Target material was extracted from the chloroform layer using 2N sodium hydroxide solution (600 mL). The basic aqueous phase was washed with chloroform (2×200 mL) to remove remaining traces of starting material. The organic layers from the basic extractions were combined and dried over anhydrous magnesium sulfate. Removal of solvents under reduced pressure resulted in recovered starting material as a bright crystalline solid (2.35 g). The basic aqueous extract was acidified to pH &lt;1 using conc. HCl (37 mL) and extracted with ethyl acetate (2×250 mL). The organic extracts were combined and dried over anhydrous magnesium sulfate. Solvents were removed under reduced pressure to yield the title compound as a yellow, powdery solid (1.82 g). 
     1,2-Dinitro-4-(1-hydroxyhexyl)oxy-5-methoxybenzene. To a solution of the methoxybenzene prepared above (270 mg, 1.259 mmol) in acetonitrile (40 mL) was added 6-bromo-1-hexanol (330 μL, 2.519 mmol), followed by sodium iodide (190 mg, 1.259 mmol) and potassium carbonate (697 mg, 5.045 mmol). The reaction was heated at 70° C. under a nitrogen atmosphere. After 5 days, the reaction mixture was cooled to 0° C. and filtered through a fine sintered glass funnel. Solvents were removed under reduced pressure and the resulting solid was dissolved in isopropyl alcohol (2 mL). The target product was precipitated by the addition of hexane (20 mL) to the rapidly stirred solution. The solid was filtered, washed with hexane and dried under reduced pressure to yield the crude target as a bright yellow solid (344 mg). Purification by short-bed silica gel chromatography using methylene chloride as the mobile phase resulted in the isolation of the product as a pale yellow crystalline solid (274 mg, 69%). 
     4-(1-Hydroxyhexyl)oxy-5-methoxy-1,2-phenylenediamine. 1,2-Dinitro-4-(1-hydroxyhexyl)oxy-5-methoxybenzene (300 mg, 0.9546 mmol) was dissolved in methanol (30 mL). Conc. HCl (1 mL) was added, followed by palladium catalyst (10% on activated carbon, 90 mg). The reaction was shaken under a hydrogen atmosphere at 45 psi. After 5 h, when the uptake of hydrogen was complete, the catalyst was removed by filtration over celite. Solvent was removed under reduced pressure to yield the target compound as the dihydrochloride salt (305 mg, 98%). 
     4, 5, 9, 24-Tetraethyl-16 (1-hydroxyhexyl)oxy-17-methoxy-pentaazapentacyclo[20.2.1.1 3 ,6.1 8 ,11.0 14 ,19 ]heptacosa-1,3,5,7,9,11(27),12,14,16,18,20,22(25),23-tridecaene. To a solution of the above phenylenediamine.2HCl (485 mg, 1.4821 mmol) in methanol (240 mL) was added solid 2,5-bis[5-formyl-3-ethyl-4-methylpyrrol-2-yl)methyl]-3,4-diethylpyrrole in one go, under a nitrogen atmosphere. After heating at 75° C. for 2 h, the reaction was allowed to cool to RT. charcoal (330 mg) was added to the solution and the system was stirred for 15 min. The charcoal was removed by filtration over celite, and the solvent was removed under reduced pressure. The target compound was isolated as the dihydrochloride salt in the form of an orange glass (900 mg, 85%). 
     Dysprosium complex of 4,5,9,24-tetraethyl-16(1-hydroxyhexyl)oxy-17-methoxy-pentaazapentacyclo[20.2.1.1 3 ,6.1 8 ,11.0 14 ,19 ]heptacosa-1,3,5,7,9,11(27),12,14,16,18,20,22(25), 23-tridecaene, cpd. 2 A . To a solution of the tridecaene prepared above (130 mg, 0.1824 mmol) in methanol (30 mL) was added dysprosium nitrate pentahydrate (120 mg, 0.2736 mmol), followed by triethylamine (260 μL, 1.834 mmol). The reaction was heated under gentle reflux open to the air. After 2.5 h, the reaction was allowed to cool to RT and was filtered through a pad of celite. Solvent was removed under reduced pressure and the resulting crude complex was triturated in acetone (30 mL) for 10 min. The solid was isolated by suction filtration and dried under reduced pressure. To remove unbound dysprosium metal ion, the complex was dissolved in a mixture off methanol/water (9:1, 15 mL) and gently agitated with zeolite (SAY-54, 600 mg), which had been previously rinsed with dilute HCl and deionized water. After 1.5 h, the zeolite was removed by filtration and the process was repeated using fresh zeolite. After removal of the zeolite, n-butyl alcohol (10 mL) was added to the system to prevent bumping during solvent removal. Solvents were removed under reduced pressure to yield the target compound 2 A  as the dinitrate salt in the form of a deep green solid (97 mg, 58%). MS (FABLR) M-HNO 3  -NO 3  796. 
     Dysprosium complex of 2-cyanoethyl-N,N-diisopropyl-6-(4,5,9,24-tetraethyl-17-methoxy-pentaazapentacyclo[20.2.1.1 3 ,6.1 8 ,11.0 14 ,19 ]-heptacosa-1,3,5,7,9,11(27), 12,14,16,18,20,22(25), 23-tridecaene-16(1-oxy)hexylphosphoramidite, cpd. 2 B . To the solid Dy complex prepared above (104 mg, 0.1129 mmol) under a strict nitrogen atmosphere was added anhydrous dichloromethane (4 mL) followed by N,N-diisopropylethylamine (79 μL, 0.4515 mmol). The system was cooled to 0° C. and 2-cyanoethyl-N,N-diisopropylchlorophosphoramidite (76 μL, 0.3386 mmol) was added via syringe. After 3.5 h, the reaction was quenched using anhydrous methanol (416 μL), and diluted using methylene chloride (8 mL). The solution was washed with saturated sodium bicarbonate (12 mL), followed by saturated sodium chloride (10 mL). The organic layer was concentrated to a volume of approximately 2 mL and added dropwise to vigorously stirring diethyl ether (46 mL). The resulting solid was isolated by centrifugation (2000 rpm, 5 min.) and washed with diethyl ether (3×46 mL), isolating the solid after each wash by centrifugation. Solvents were removed under reduced pressure to yield the title compound 2 B  as a deep green solid (80 mg). ##STR3## 
     EXAMPLE 3 
     Preparation of a Dual Texaphyrin Phosphoramidite 
     Following the procedures of Example 2, a dual texaphyrin phosphoramidite 3 B  may be prepared from the DyTx complex 3 A  (2 eq. ). ##STR4## 
     Such a dual texaphyrin phosphoramidite is useful in preparing a texaphyrin-oligonucleotide conjugate having two texaphyrin macrocycles at the terminus of the oligonucleotide, which conjugate would be expected to have greater hydrolytic or photolytic cleavage activity of an RNA or DNA, for example. 
     All of the compositions and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the composition, methods, and in the steps or in the sequence of steps of the method described herein without departing from the concept, spirit, and scope of the invention. More specifically, it will be apparent that certain agents which are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope, and concept of the invention as defined by the appended claims.