Date of Degree
Mahesh K. Lakshman
Stephen P. Fearnley
Nucleic Acids, Nucleotides, and Nucleosides | Organic Chemicals | Polycyclic Compounds
Nucleoside Modification, Deuterated Triazoles, Hippadine
The C4 amide carbonyl of O-t-butyldimethylsilyl-protected thymidine, 2’-deoxyuridine, and 3’-azidothymidine (AZT) was activated by reaction with (benzotriazol-1-yloxy)tris(dimethylamino) phosphonium hexafluorophosphate (BOP) and 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in THF as solvent. This led to the formation of corresponding O4-(benzotriazol-1-yl) derivatives, which are reactive intermediates. Substitution at the C4 position was then carried out by reactions with alkyl and aryl amines, and thiols. Typically, reactions were conducted as a two-step, one-pot transformation, and also as a one-step conversion. After examining the reactions, the formation of 1-(4-pyrimidinyl)-1H-benzotriazole-3-oxide derivatives from the pyrimidine nucleosides was identified. However, these too underwent conversion to the desired products. C4 modified pyrimidine nucleosides were desilylated using standard conditions. Desilylated 3’-azido derivatives obtained from AZT were also converted to the 3’-amino derivatives by catalytic reduction. All products were evaluated for their abilities to inhibit cancer cell proliferation and for antiviral activities. Some compounds displayed moderate inhibitory activity against proliferation of murine leukemia (L1210), human cervix carcinoma (HeLa), and human T-lymphocytic (CEM) cell lines. Many were seen to be active against HIV-1 and HIV-2, and one was active against herpes simplex virus-1 (HSV-1). Evaluations of the structures and activities indicated that the methyl group at the C5 position is important for biological activity.
Chemoselective N-arylation of 8-vinyladenine nucleosides can be carried out with the Pd(OAc)2/Xantphos/Cs2CO3 combination. All the other ligands such as DPEPhos, DPPF, and BIPHEP in combination with Pd(OAc)2, and the complex Pd-118 resulted in Heck arylation, exclusively. Both aryl iodides and bromides can be used under these conditions. Generally, all reactions resulted in N-arylated products in good yields, along with small amounts of Heck-like products and C,N-diarylated products. However, the Heck-like products were observed mostly in the reactions of aryl iodides. The results from the Pd-catalyzed N-arylation reactions of deoxy and ribonucleosides were very similar, but a higher catalyst loading and temperature for reactions of the ribonucleoside was required. A modular, one-pot approach was utilized for the synthesis of diaryl products via sequential C–C reaction and C–N arylation. The generality of chemoselective arylation of simple substrates was tested by exposing p-aminostyrene under N-arylation and Heck-arylation conditions. The results indicated that in this case as well, the Pd/Xantphos/Cs2CO3 combination was effective for chemoselective N-arylation and the Pd/DPEPhos/Cs2CO3 combination was effective for chemoselective Heck-arylation.
In order to synthesize nucleosides adducts produced by a cis ring-opening of benzo[a]pyrene diol epoxide 1, diastereoselective synthesis of (±)-10β-amino-7β,8α,9β-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene was carried out in nine steps from (±)-7β,8α-dibenzoyloxy-7,8,9,10-tetrahydrobenzo[a]pyrene. The (±)-7β,8α-dibenzoyloxy-7,8-dihydrobenzo[a]pyrene was converted to the diol epoxide and then reacted with lithium chloride and acetic anhydride to give a peracyl trans chloro triol with a chloride at the benzylic position. Displacement of chloride by azide, followed by deacylation, and reduction of the azide afforded the requisite amino triol. B[a]P-deoxyadenosine adducts were synthesized by the reaction of this amino triol with a 6-fluoropurine 2’-deoxyriboside derivative. The two adducts obtained from this reaction were separated by preparative TLC and the chirality in each was assigned by comparing their circular dichroism data with the literature. The 2-fluoro-2’-deoxyinosine derivative required for the synthesis of B[a]P-deoxyguanosine adducts, was synthesized by a modified approach utilizing a C6 modification protocol for guanosine nucleosides via the amide activation by BOP. However, the reaction of 2-fluoro-2’-deoxyinosine derivative with the amino triol was unsuccessful. Hence, the hydrochloride salt of amino triol was prepared and then reacted with 2-fluoro-2’-deoxyinosine derivative. This reaction yielded two B[a]P-deoxyguanosine adducts, which were separated by preparative TLC and the chirality in each was assigned by comparing their circular dichroism data with literature. However, careful NMR analysis of B[a]P-dA and dG adducts indicated that the products were not the anticipated cis ring-opened nucleoside adducts as previously reported, but the data were more consistent with trans ring-opened B[a]P DE1-nucleoside adducts. This information suggested that the amino triol synthesized had the undesired trans stereochemistry at the C9 and C10 positions. This was further confirmed by careful evaluation of chemical shift and coupling constant data of synthesized azido triol with known data of trans and cis ring-opened azido triols.
By utilizing PPh3/I2 mediated amidation reaction as a key step, a simple approach was developed for the synthesis of hippadine via anhydrolycorinone. N-(Piperonoyl)indoline was synthesized by reacting piperonylic acid and indoline in the presence of PPh3/I2 andiPr2NEt. The combination of polymer-supported PPh3/I2 in place of PPh3/I2 was also very effective under these conditions, and both combinations gave comparable yields of N-(piperonoyl)indoline. However, in CDCl3, the 1H NMR data of the amide obtained was missing one aromatic resonance. The structure of amide obtained via these amidation reactions was further confirmed by obtaining 1H NMR in C6D6 at 70 °C and COSY data. The amide was then cyclized using PhI(OTFA)2 and BF3 to give anhydrolycorinone that was finally oxidized by DDQ to give hippadine in an overall yield of 13%, over three steps.
Deuteration at the C-5 position of the 1,2,3-triazole structure was carried out efficiently during the triazole-forming step by using a copper-catalyzed azide−alkyne cycloaddition (CuAAC) reaction. Reactions of alkynes and azides were conducted in a biphasic medium of CH2Cl2/ D2O, using the CuSO4 and Na ascorbate. The mild reaction conditions allow the applicability of this method to relatively high complex substrates, such as nucleosides. Generally, good yields and high levels of deuterium incorporation were observed in all cases. Using appropriately deuterated precursors, partially to fully deuterated triazoles were also assembled under the same conditions. The competition of deuteration vs protonation in the CuAAC reaction was evaluated by conducting a reaction of phenyl azide with 4-ethynyltoluene with equimolar H2O and D2O. Higher hydrogen atom incorporation in the triazole products was observed as compared to deuterium (protonated vs deuterated triazoles were obtained in a 2.7:1 ratio).
Akula, Hari K., "Catalyzed and Uncatalyzed Modifications of Nucleosides, Synthesis of Hippadine, and Deuterated 1,2,3-Triazoles" (2018). CUNY Academic Works.