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DOI: 10.1055/a-2322-3741
Evaluation of Transiently O-6-Protected Guanosine Morpholino Nucleosides in Phosphorodiamidate Morpholino Oligonucleotide Synthesis
S.S. thanks the Science and Engineering Research Board (SERB), New Delhi, Government of India (TTR/2021/000044) and the Department of Science and Technology (DST), New Delhi (DST/TDT/TC/RARE/2022/10c2) for grant support. M.Q. thanks the University Grants Commission (UGC), New Delhi and A.G. and A.D. thank the Council of Scientific and Industrial Research (CSIR) for their fellowships.
Abstract
A novel strategy is presented for the synthesis of morpholino guanosine monomers protected at O-6 with 1-(4-azidophenyl)ethan-1-ol, p-methoxybenzyl alcohol and trimethylsilylethyl groups. The introduction of these protecting groups increases the solubility of the morpholino nucleosides which is crucial during the synthesis of phosphorodiamidate morpholino oligonucleotides (PMOs). HPLC analysis shows that the trimethylsilylethyl-protected monomer gives better coupling efficiency in PMO synthesis compared to the regular monomer. Moreover the nonpolar nature of the O-6-protected monomer facilitates the preparation of guanosine-rich oligomer in solution.
Key words
antisense agents - bioorganic chemistry - oligonucleotides - protecting groups - solid-phase synthesisSupporting Information
- Supporting information for this article is available online at https://doi.org/10.1055/a-2322-3741.
- Supporting Information
Publication History
Received: 24 July 2023
Accepted: 08 May 2024
Accepted Manuscript online:
08 May 2024
Article published online:
27 May 2024
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- 21 To a stirred solution of 4a (202 mg, 0.3 mmol, 1 equiv.) in dry (1:1) CH3CN: DCM at 0 °C were added LiBr (1.12 mmol, 4 equiv.), tetramethylguanidine (1.12 mmol, 4 equiv.) and POCl2NMe 2 (0.84 mmol, 3 equiv.). Then the reaction mixture was left for 15 min at 0° C. TLC showed complete consumption of the starting material. After completion of the reaction (TLC analysis), the solvent was evaporated in vacuo and re-dissolved in EtOAc. The organic layer was washed with water and saturated aq. NH4Cl. The organic layer was then dried on anhydrous Na2SO4 and solvent was evaporated in vacuo. The crude mixture was purified by silica gel (60-120 mesh) column chromatography eluting with Acetone-DCM to obtain the compound 5a in 60% yield (143 mg) (Rf = 0.6 in 3.5% MeOH-DCM).1H NMR (300 MHz, CDCl3): δ 7.84 – 7.72 (m, 2H), 7.59 – 7.34 (m, 10H), 7.34 – 7.27 (m, 6H), 7.19 (q, J = 5.8 Hz, 3H), 7.01 – 6.89 (m, 2H), 6.42 (q, J = 6.6 Hz, 1H), 6.21 (dt, J = 9.7, 2.3 Hz, 1H), 4.54 – 4.41 (m, 1H), 4.11 (ddd, J = 8.9, 6.0, 3.4 Hz, 1H), 3.44 (d, J = 11.6 Hz, 1H), 3.26 – 3.08 (m, 2H), 2.62 (dd, J = 13.9, 4.9 Hz, 6H), 1.74 – 1.69 (m, 3H), 1.55 (dd, J = 10.7, 3.2 Hz, 1H), 1.35 (d, J = 6.9 Hz, 3H), 1.31 – 1.24 (m, 7H) ppm. 13C NMR (75 MHz, CDCl3): δ 178.0, 176.1, 160.3, 152.3, 152.0, 147.4, 139.5, 139.0, 138.9, 138.7, 136.5, 135.6, 135.6, 129.9, 129.2, 128.1, 128.0, 127.9, 127.8, 127.0, 126.8, 126.6, 119.1, 119.1, 118.0, 80.6, 80.5, 77.6, 77.4, 77.2, 77.0, 76.7, 74.7, 74.6, 69.6, 67.2, 64.6, 53.9, 53.1, 49.1, 49.0, 36.7, 35.5, 31.8, 29.8, 29.4, 26.8, 22.8, 19.6, 19.5, 19.4, 19.3, 19.1, 19.0, 14.2 ppm. 31P NMR (121 MHz, CDCl3): δ 18.5, 18.2 ppm. IR (CHCl3, cm-1): 2980, 2929, 2102, 1716, 1601, 1508, 1249, 1050, 712.HRMS(ESI)[M+H]+: Mass calculated for C43H47ClN10O5P was 849.3152, found 849.3159.Synthesis of compound 5b: Compound 5b was synthesized from 4b (265 mg, 0.38 mmol, 1 equiv.) following the procedure of 5a in 60% yield (188mg). Rf: 0.5 (3.5% MeOH-DCM).1H NMR (300 MHz, CDCl3): δ 7.80 (s, 1H), 7.75 (d, J = 3.0 Hz, 1H), 7.53 – 7.38 (m, 7H), 7.36 – 7.26 (m, 7H), 7.19 (t, J = 7.3 Hz, 3H), 6.94 – 6.81 (m, 3H), 6.39 – 6.06 (m, 1H), 5.61 – 5.47 (m, 2H), 4.54 – 4.41 (m, 1H), 4.10 (tt, J = 7.9, 3.8 Hz, 2H), 3.79 (s, 3H), 3.46 (d, J = 11.4 Hz, 1H), 3.22 (d, J = 11.9 Hz, 2H), 2.61 (dd, J = 13.9, 5.8 Hz, 6H), 1.35 (t, J = 6.5 Hz, 6H) ppm. 13C NMR (75 MHz, CDCl3): δ 160.5, 159.3, 151.9, 151.7, 138.6, 138.5, 132.8, 129.9, 128.8, 128.3, 127.7, 127.6, 126.4, 117.5, 113.7, 113.5, 80.0, 77.1, 76.9, 76.7, 76.3, 74.3, 74.2, 68.3, 66.8, 64.8, 55.0, 52.6, 48.6, 36.3, 36.3, 35.2, 29.4, 19.1, -0.32 ppm. 31P NMR (121 MHz, CDCl3): δ 18.5, 18.2 ppm. IR (CHCl3, cm-1): 2931, 1709, 1607, 1513, 1242, 1027, 747. HRMS. (ESI) [M + Na]+: Mass calculated for C43H47ClN7NaO6P was 846.2906, found 846.2910.
- 22 Synthesis of compound 11: Compound 11 was synthesized from compound 10 (484 mg, 0.7 mmol, 1 equiv.) following the procedure of 5a in 66% yield (369mg). Rf: 0.6 (3.5% MeOH-DCM). 1H NMR (300 MHz, CDCl3): δ 7.87 (s, 1H), 7.75 (d, J = 3.1 Hz, 1H), 7.47 (d, J = 7.6 Hz, 6H), 7.29 (t, J = 7.6 Hz, 6H), 7.18 (t, J = 7.3 Hz, 3H), 6.25 (dt, J = 9.7, 2.2 Hz, 1H), 4.69 – 4.53 (m, 2H), 4.53 – 4.42 (m, 1H), 4.18 – 4.03 (m, 2H), 3.52 – 3.41 (m, 1H), 3.37 (s, 1H), 3.23 (dd, J = 11.6, 2.4 Hz, 1H), 2.60 (dd, J = 13.9, 5.7 Hz, 6H), 1.77 (ddd, J = 11.3, 9.9, 3.0 Hz, 1H), 1.66 – 1.51 (m, 1H), 1.34 (t, J = 6.8 Hz, 6H), 1.26 – 1.16 (m, 3H), 0.08 (s, 9H) ppm. 13C NMR (75 MHz, CDCl3): δ 176.8, 161.1, 152.2, 152.1, 138.8, 138.8, 129.2, 128.0, 126.7, 117.8, 80.3, 77.6, 77.4, 77.2, 77.0, 76.7, 74.7, 74.6, 67.2, 67.2, 65.9, 53.0, 49.0, 36.7, 36.6, 35.1, 19.5, 19.4, 17.5, -1.3, -1.7 ppm. 31P NMR (121MHz, CDCl3): δ 18.5, 18.1 ppm. IR (CHCl3, cm-1): 2953, 1688, 1603, 1250, 1030, 712. HRMS (ESI) [M + H]+: Mass calculated for C40H52N7O5SiP was 804.3220 , found 804.3224.