Mannich-Type C-Nucleosidations with 7-Carba-purines and 4-Aminopyrimidines

Bo Han; Vivek Rajwanshi; Jyoti Nandy; Ramanarayanan Krishnamurthy; Albert Eschenmoser

doi:10.1055/s-2005-864789

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Synlett 2005(5): 0744-0750
DOI: 10.1055/s-2005-864789

LETTER

Mannich-Type C-Nucleosidations with 7-Carba-purines and 4-Aminopyrimidines [1]

Bo Han^a, Vivek Rajwanshi^b, Jyoti Nandy^b, Ramanarayanan Krishnamurthy*^b, Albert Eschenmoser*^a,b
^a Laboratory of Organic Chemistry, Swiss Federal Institute of Technology, Hönggerberg, HCI-H309, 8093 Zürich, Switzerland
^b The Skaggs Institute of Chemical Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA
Fax: +1(858)7849573; e-Mail: rkrishna@scripps.edu;

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Publication History

Received 3 November 2004
Publication Date:
09 March 2005 (online)

Abstract
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Abstract

Regioselective Mannich-type C-nucleosidations of pyrroline derivatives 3 and 8 with 7-carba-purines and 4-aminopyrimidines occur under mild conditions to afford C(8)- and C(5)-azanucleosides, respectively.

Key words

C-azanucleosides - Mannich reaction - electrophilic substitution - heterocycles - 7-carba-purine - pyrimidines - pyrrolines

1

Chemistry of α-aminonitriles. Part 43. For Part 42, see ref. 3.

References

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1

Chemistry of α-aminonitriles. Part 43. For Part 42, see ref. 3.

8

Attempts to obtain the isoguanine analog 2b ⁶ in this series, starting from 1b, following this protocol were not successful. Instead, a compound identified as 5-aza-3,7-dicarbaguanine⁹ was isolated in ca. 13% yield.

10

Bocylation also prevented the (unwanted) O→N migration of the 2′,3′-O-benzoyl groups.

11

A minor product (ca. 10%) was isolated and was tentatively identified as the expected C(5)-azanucleoside; unreacted starting materials were recovered up to ca. 60%. In a follow-up experiment the C(5)-azanucleoside product from the reaction 1a and 3 was debocylated (with sat. HCl in anhyd Et₂O) affording the NH-unprotected free C(5)-nucleoside; when this debocylated intermediate was subjected to the nucleosidation reaction conditions (condition a, Scheme [1] ), formation of the pyrimidine base 1a was observed (TLC, ¹H NMR and MS).

12

Reaction with carba-purine 2d was not attempted.

13

X-ray structure analysis of 11α was carried out by Dr. Bernd Schweizer, ETHZ. Crystallographic data for the structure has been deposited with the Cambridge Crystallographic Data Centre as deposition no. CCDC 249544. Copies of the data can be obtained, free of charge, on application to the CCDC, 12 union Road, Cambridge CB12 1EZ, UK [fax +44 (1233)3360333; e-mail: deposit@ccdc.cam.ac.uk].

14

Pyrroline 3 is more reactive than pyrroline 8; see footnote 13 of ref. 2b.

15

In this context it is of interest to note that no, or inefficient, formation of C-nucleosides were observed when Schiff bases from aldosugar derivatives of l-α-di-O-benzoyl-threose or 2,3-acetonide of d-ribofuranose were used in place of pyrrolines 3 or 8 (see also Scheme [4] in ref. 2b).

16

In a deuterium incorporation study (pH 5-6, CD₃CO₂D, DMSO-d ₆, D₂O, r.t.) of the four pyrimidines 1a-d, the H-C(5) proton was exchanged to D-C(5) most rapidly in 1a (87% in 5 min), followed by 1c (84% in 5 min), 1d (69% in 5 min) and 1b (2% in 5 min; 85% after 24 h).

19

C-Nucleosidation of (3 S ,4 S )-3,4-Dibenzoyloxypyrroline (Scheme 1). Representative Procedure.2,4-Diamino-5-[ N -( tert -butyloxycarbonyl)-(2′ S ,3′ S )-2′,3′-dibenzoyloxy-(1′ S )-pyrrolidinyl]-6-oxopyrimidine (4α). The amount of 927 mg (1.0 mmol) of pyrroline-trimer 3 and 190 mg (1.0 mmol) p-TsOH·H₂O was dissolved in 10 mL of DMF, to which 126 mg (1.0 mmol) of pyrimidine 1c was added in one portion and stirred at r.t. for 2 h. TLC, (CH₂Cl₂-MeOH-25% aq NH₃) indicated that pyrimidine (R _f =0.25) totally disappeared, and a new UV active spot (R _f = 0.76) was formed. Then, 404 mg (4.0 mmol) of Et₃N and 250 mg (1.1 mmol) of Boc₂O was added to the above reaction solution and stirred at r.t. for 30 min. TLC (CH₂Cl₂-MeOH-25% aq NH₃) showed that the R _f = 0.76 spot was converted to another spot (R _f = 0.81). Evaporation of solvent under reduced pressure at 55 °C gave a light brown oil, which was purified by CC (silica gel, CH₂Cl₂-MeOH 100:8). Fractions 15-28 (10 mL each) were combined and evaporated under reduced pressure at 40 °C to give 492 mg (92%) of 4α as amorphous light yellow solid; mp (EtOAc): >190 °C. TLC: R _f = 0.31 CH₂Cl₂-MeOH (10:1). ¹H NMR (300 MHz, DMSO-d ₆, 100 °C): δ = 1.34 (s, 9 H, Me), 3.75 [dd, ² J _H-H = 10.6 Hz, ³ J _H-H = 8.1 Hz, 1 H, H-C(4′)], 4.16 [dd, ² J _H-H = 10.6 Hz, ³ J _H-H = 7.6 Hz, 1 H, H-C(4′)], 4.86 [d, J = 5.6 Hz, 1 H, H-C(1′)], 5.47 [ddd, J _trans-H4 _′ _-H3 _′ = J _cis-H4 _′ _-H3 _′ = 7.9 Hz, J _H2 _′ _-H3 _′ = 6.2 Hz, 1 H, H-C(3′)], 5.62 (br s, NH₂, 2 H, exchanges with D₂O), 5.89 (br s, 2 H, NH₂, exchanges with D₂O), 6.15 [dd, J _H1 _′ _-H2 = J _H3 _′ _-H2 _′ = 5.8 Hz, 1 H, H-C(2′)], 7.47-8.01 (m, 10 H, C₆H₅), 9.65 (s, 1 H, NH, exchanges with D₂O). ¹³C NMR [75.45 MHz, DMSO-d ₆): δ = 28.14 (q), 48.49 (t), 56.00 (d), 74.40 (d), 78.47 (d), 85.69 (s), 128.44 (d), 128.58 (d), 128.95 (s), 129.12 (d), 129.37 (d), 133.29 (d), 133.41 (d), 152.92 (s), 153.00 (s), 161.32 (s), 162.46 (s), 164.98 (s), 165.09 (s). MALDI-MS: m/z (%) = 558.1(51) [M + Na]⁺, 536.2 (34) [M + H]⁺), 458.1(33) [M - Boc + Na]⁺, 436.1(100) [M - Boc + H]⁺). HR-MALDI: m/z calcd for C₂₇H₂₉N₅O₇Na [M + Na⁺]: 558.1959; found: 558.1965. UV (c = 5·10^-5 M in MeOH): λ_max = 273 nm (ε = 1.40·10⁴), 230 (2.98·10⁴), 215 (3.23·10⁴); λ_min = 253 nm(6500), 224 (2.84·10⁴), 206 (2.67·10⁴). Anal. Calcd for C₂₇H₂₉N₅O₇: C, 60.55; H, 5.46; N, 13.08; Found C, 60.45; H, 5.57; N, 12.82.
4-Amino-5-[ N -( tert -butyloxycarbonyl)-(2′S ,3′S )-2′,3′-dibenzoyloxy-(1′S )-pyrrolidinyl]-2,6-dioxopyrimidine (5α).
Mp >200 °C(decomp). TLC: R _f = 0.33 (CH₂Cl₂-MeOH, 10:1). ¹H NMR (300 MHz, DMSO-d ₆, 100 °C): 1.39 (s, 9 H, Me), 3.72 [dd, ² J _H-H = 10.6 Hz, ³ J _H-H = 8.4 Hz, 1 H, H-C(4′)], 4.14 [dd, ² J _H-H = 10.6 Hz, ³ J _H-H = 8.1 Hz,, 1 H, H-C(4′)], 4.83 [d, J = 6.0 Hz, 1 H, H-C(1′)], 5.45 [‘q’, J _H2 _′ _-H3 _′ = J _cis-H4 _′ _-H3 _′ = J _trans-H4 _′ _-H3 _′ = 8.7 Hz, 1 H, H-C(3′)], 6.01 (br s, 2 H, NH₂, exchanges with D₂O), 6.09 [dd, J_H1 _′ _-H2 = J _H3 _′ _-H2 _′ = 6.3 Hz, 1 H, H-C(2′)], 7.49-7.80 (m, 10 H, C₆H₅), 9.97 (s, 1 H, NH, exchanges with D₂O), 10.36 (s, 1 H, NH, exchange with D₂O). ¹³C NMR (75.45 MHz, DMSO-d ₆): 28.1 (q), 48.4 (t), 56.0 (d), 74.5 (d), 78.5 (d), 85.8 (s), 128.6 (d), 128.8 (d), 129.1 (s), 129.3 (d), 129.6 (d), 133.5 (d), 133.6 (d), 153.1 (s), 153.7 (s), 161.6 (s), 162.7 (s), 165.2 (s), 165.3 (s). MALDI-MS: m/z (%) = 559.2(60) [M + Na]⁺, 459.1(68) [M - C₆H₅]⁺, 437.1(100) [M - Boc + H⁺]. HR-MALDI: m/z calcd for C₂₇H₂₈N₄O₈Na [M + Na⁺]: 559.1719; found: 559.1811. UV (c = 5·10^-5 M in MeOH): λ_max = 266 nm (ε = 1.83·10⁴), 230 (3.26·10⁴), λ_min = 249 (9500), 210 (1.18·10⁴). Anal. Calcd for C₂₇H₃₀N₄O₈·H₂O: C, 58.48; H, 5.45; N, 10.10. Found: C, 58.71; H, 5.60; N, 10.14.
Data for C-nucleoside product isolated from reaction 1a with 3: ¹H NMR (600 MHz, DMSO-d ₆, 70 °C): 1.30 (s, 9 H, Me), 3.76 [dd, 1 H, J = 6.8, 12.0, H-C(4′)], 4.14 [dd, 1 H, J = 7.9, 12.0 Hz, H-C(4′)], 5.14 [d, 1 H, J = 7.4 Hz, H-C(1′)], 5.30 (br s, 2 H, -NH₂), 5.49 [m, 5 H, H-C(3′), 2 NH₂], 5.82 [d, 1 H, J = 6.7 Hz, 1 H, H-C(2′)], 7.37-8.02 (m, 10 H, arom. H). EI-MS (pos., MeOH): m/z (%) = 557 (100) [M + Na]⁺), 535 (40) [M + H]⁺), 435 (20) [M - BOC]⁺). EI-MS (neg., MeOH): m/z (%) = 569 (80) [M + Cl]^-.
8-[ N -( tert -Butyloxycarbonyl)-(2′S ,3′S )-2′,3′-(dibenzoyloxy)pyrrolidinyl]-7-carba-guanine (6α/β). Representative Procedure.
A mixture of 432.6 mg (0.47 mmol) of pyrroline-trimer 3 and 89.0 mg (0.47 mmol) of p-TsOH·H₂O was dissolved in 4.7 mL of dry DMF (molecular sieves), to which 70.6 mg (0.47 mmol) of purine 2c was added in one portion and stirred at 50 °C for 5 h [after 5 h, TLC (CH₂Cl₂-MeOH-aq NH₃, 9:1:0.1) showed the disappearance of 2c and presence of two spots (R _f = 0.22, 0.19)]. To this reaction mixture was added 0.27 mL (1.88 mmol) of Et₃N followed by 102.6 mg (0.47 mmol) of Boc₂O and stirred at 50 °C for next 2 h (after 2 h, spots at R _f = 0.22 and 0.19 disappeared and two new UV active spots at R _f = 0.3 and 0.27 were observed on TLC). Evaporation of the solvents (45 °C) under reduced pressure (rotavap.) followed by drying under high vacuum (0.3 mbar, 12 h) gave crude residue as yellow sticky solid, which was redissolved in CH₂Cl₂ and purified by CC (silica gel, CH₂Cl₂-MeOH 98:2 to 93:7). Fractions (33-70, 10 mL each) eluted with 3% MeOH in CH₂Cl₂ were combined and concentrated in vacuo to afford 89.4 mg (34%) of 6α as off white solid. Fractions (71-103) eluted with 3-5% MeOH in CH₂Cl₂ were combined and concentrated in vacuo to give 139.2 mg (53%) of a mixture of epimers of 6, which was re-purified by CC (silica gel, CH₂Cl₂-MeOH 98:2 to 94:6). Fractions (45-67) eluted with 2.5% MeOH in CH₂Cl₂ were combined and concentrated in vacuo to give 17.0 mg (6.5%) of 6α [identical (¹H NMR) with the epimer of 6 isolated before] as an off-white solid. Fractions (72-115) eluted with 2.5-3.5% MeOH in CH₂Cl₂ were combined and concentrated in vacuo to afford 66.6 mg (25.4%) of the other β-epimer of 6. Thus, overall isolated yields after two CCs are 40.5% for 6α and 25.4% for 6β. Purity was greater than 95% by ¹H NMR.
Analytical data of 6α: TLC: R _f = 0.22 (MeOH-aq NH₃, 9:1:0.1). ¹H NMR (600 MHz, DMSO-d ₆, 70 °C): δ = 1.38 (s, 9 H, 3 Me), 3.79 [dd, J = 2.7, 12.9 Hz, 1 H, H-C(4′)], 4.16 [dd, J = 6.2, 12.7 Hz, 1 H, H-C(4′)], 5.11 [br s, 1 H, H-C(2′)], 5.57 (dd, J = 3.2, 6.1 Hz, 1 H, H-C(3′)], 5.62 [br s, 1 H, H-C(1′)], 5.92 (s, 2 H, -NH₂), 6.14 [s, 1 H, H-C(7)], 7.37-8.02 (m, 10 H, arom. H), 10.19 (br s, 1, -NH-), 10.87 (br s, 1 H, -NH-). ¹³C NMR (150.9 MHz, DMSO-d ₆, 70 °C): δ = 28.89 (q, Me), 51.40 [d, C(4′)], 60.93 [d, C(2′)], 75.71 [d, C(3′)], 80.35 (s, CMe₃), 81.29 [d, C(1′)], 100.04 [d, C(7)], 101.01, 128.89, 129.27, 129.61, 129.92, 130.06, 130.26, 134.29, 134.53, 152.39, 153.22, 154.5 (arom. C), 159.41, 165.55 (2 s, C=O). ESI-MS (pos., MeOH): m/z (%) = 598 (25) [M + K]⁺, 582 (100) [M + Na]⁺. ESI-MS (neg., MeOH): m/z (%) = 594 (35) [M + Cl]^-, 558 (100) [M - H]^-.
Data for 6β: TLC: R _f = 0.19 (MeOH-aq. NH₃, 9:1:0.1). ¹H NMR (600 MHz, DMSO-d ₆, 70 °C): δ = 1.31 (s, 9 H, 3Me), 3.71 [dd, J = 3.2, 8.9 Hz, 1 H, H-C(4′)], 4.18 [dd, J = 5.8, 9.4 Hz, 1 H, H-C(4′)], 5.31 [d, J = 4.3 Hz, 1 H, H-C(2′)], 5.63 [m, 1 H, H-C(3′)], 5.77 [br m, 1 H, H-C(1′)], 5.79 (br s, 2 H, NH₂), 6.06 [s, 1 H, H-C(7)], 7.35-8.06 (m, 10 H, arom. H), 9.94 (br s, 1 H, -NH-), 10.84 (br s, 1 H, -NH-). ¹³C NMR (150.9 MHz, DMSO-d ₆, 70 °C): δ = 28.83 (q, Me), 49.82 [d, C(4′)], 57.39 [d, C(2′)], 75.29 [d, C(3′)], 76.75 [d, C(1′)], 80.17 (s, CMe₃), 100.84, 101.05 [d, C(7)], 127.41, 129.3, 129.60, 130.0, 130.09, 130.13, 130.17, 134.22, 134.5, 149.3, 152.18, 152.93, 154.61 (arom. C), 159.3, 165.4, 165.84 [s, C=O). ESI-MS (pos., MeOH): m/z (%) = 582 (10) [M + Na]⁺), 560 (30) [M + H]⁺). ESI-MS (neg., MeOH): m/z (%) = 558 (40) [M - H]^-.
8-[ N -( tert -Butyloxycarbonyl)-(2′S ,3′S )-2′,3′-(dibenzoyloxy)pyrrolidinyl]-7-carba-xanthine (7α/β).
Overall isolated yield of the two epimers, after purification by CC, is 67.5% (the ratio of the α- and β-epimers in the crude residue is 2:1).
Data for 7α: TLC: R _f = 0.34 (CH₂Cl₂-MeOH, 19:1). ¹H NMR (600 MHz, DMSO-d ₆, 70 °C): δ = 1.40 (s, 9 H, Me), 3.75 [dd, J = 2.3, 12.7 Hz, 1 H, H-C(4′)], 4.15 [dd, J = 5.9, 12.7 Hz, 1 H, H-C(4′)], 5.11 [s, 1 H, H-C(1′)], 5.59 [m, 1 H, H-C(3′)], 5.62 [s, 1 H, H-C(2′)], 6.19 [s, 1 H, H-C(7)], 7.39-8.03, (m, 10 H, arom. H), 10.13 (br s, NH, 0.6 H), 10.90 (br s, NH, 1 H). ¹³C NMR (150.9 MHz, DMSO-d ₆, 70 °C): δ = 28.86 (q, Me), 51.47 [t, C(4′)], 60.54 [d, C(1′)], 75.62 [d, (C3′)], 80.49 [d, C(2′)], 80.73 (s, CMe₃), 99.14 [s, C(5)], 101.21 [d, C(7)], 128.45 [s, C(8)], 128.45, 129.13, 129.46, 129.64, 129.76, 129.97, 130.09, 134.20, 134.45 (arom. C), 139.79 [s, C(4)], 151.47 [s, C(2)], 154.34 (arom. C), 160.12 [s, H(C6)], 165.19 (s, C=O), 165.27 (C=O), 173.0 (s, C=O). ESI-MS (pos., MeOH): m/z (%) = 599 (10) [M + K]⁺), 583 (100) [M + Na]⁺, 561 (25) [M + H]⁺), 461 (20) [M - Boc + H]⁺). ESI-MS (neg., MeOH): m/z (%) = 595 (10) [M + Cl]^-, 559 (80) [M - H]^-.
Data for 7β: TLC: R _f = 0.29 (CH₂Cl₂-MeOH, 19:1). ¹H NMR (600 M Hz, DMSO-d ₆, 70 °C): δ = 1.32 (s, 9 H, Me), 3.75 [dd, J = 3.54, 12.15 Hz, 1 H, H-C(4′)], 4.13 [dd, J = 5.52, 12.05 Hz, 1 H, H-C(4′)], 5.34 [m, 1 H, H-C(1′)], 5.58 [m, 1 H, H-C(3′)], 5.78 [m, 1 H, H-C(2′)], 6.09 [s, 1 H, H-C(7)], 7.43-8.00, [m, 10 H, arom. H), 10.02 (br s, 0.7 H), 10.98 (br s, 1 H). ESI-MS (pos., MeOH): m/z (%) = 583 (100) [M + Na]⁺, 561 (25) [M + H]⁺), 461(25) [M - Boc + H]⁺). ESI-MS (neg., MeOH): m/z (%) = 595 (5) [M + Cl]^-, 559 (100) [M - H]^-).
C-Nucleosidation of (3 R ,4 S )-3,4-Di( tert -butyloxy-carbonylamino)pyrroline (Scheme 2). Representative Procedure. 2,4-Diamino-5-[ N -( tert -butyloxycarbonyl)-(2′ R ,3′S)-2′,3′-di( tert -butyloxycabonylamino)-(1′ S )-pyrrolidinyl]-6-oxopyrimidine (9α/β).
A mixture of 360 mg (1.2 mmol) of compound 8 and 190 mg (1.0 mmol) of p-TsOH·H₂O was dissolved in 10 mL of DMF, to which 126 mg (1.0 mmol) of pyrimidine 1c was added all in one portion and the mixture was stirred at r.t. for 2 h. TLC (CH₂Cl₂-MeOH-25% aq NH₃, 4:1:0.2) showed the total consumption of 1c (R_f = 0.21) and the formation of a new main spot (R_f = 0.32). Then, 404 mg (4.0 mmol) of Et₃N and 250 mg (1.1 mmol) of Boc₂O were added and the reaction mixture was stirred at r.t. for 30 min. TLC (CH₂Cl₂-MeOH-25% aq NH₃, 4:1:0.2) showed that the spot (R_f = 0.24) was converted to another spot (R_f = 0.88). After evaporation of the solvent under reduced pressure (at 55 °C), 250 mL of EtOAc was added, the organic layer washed with H₂O (3 × 50 mL) and dried (Na₂SO₄). Removal of solvent gave a light brown solid, which was purified by CC (silica gel, CH₂Cl₂-MeOH. 100:10). Fractions 16-35 (5 mL each) were combined and evaporated under reduced pressure at 40 °C to give 413 mg (78%, α/β = 9:1, by ¹H NMR) of 9α/β as light yellow solid. Crystallization of 400 mg of epimeric mixture from EtOAc-hexane gave 203 mg (51%) of pure 9α. Mp >202 °C (decomp.). TLC: R_f = 0.09 (CH₂Cl₂-MeOH, 100:10). ¹H NMR (300 MHz, DMSO-d ₆, 100 °C): δ = 1.31 (s, 9 H, 3 CH₃), 1.38 (s, 9 H, 3 CH₃), 1.39 (s, 9 H, 3 CH₃), 3.24 [dd, ² J _H-H = 10.0 Hz, ³ J _H-H = 8.8 Hz, 1 H, trans-H-C(4′)], 3.78 [m, 2 H, cis-H-C(4′) and H-C(3′)], 4.05 [m, 1 H, H-C(2′)], 4.42 (d, J = 5.6 Hz, 1 H, H-1′), 5.63 (br s, 2 H, NH₂), 5.85 (br s, 2 H, NH₂), 6.68 (br s, 1 H, NHBoc), 6.75 (br s, 1 H, NHBoc), 9.67 (br s, 1 H, NH). ¹³C NMR (75 MHz, DMSO-d ₆, 100 °C): δ = 28.19 [q, (CH₃)₃C], 50.34 [t, C(4′)], 54.21 (d), 57.73 (d), 59.95 (d), 78.88 (s, Me₃C), 78.29 (s, Me₃C), 87.52 (s, C-6), 153.18 (s), 153.35 (s), 154.87 (s), 155.62 (s), 161.41 (s), 162.38 (s). UV (c = 5·10^-5 M in MeOH): λ_max = 213 nm (ε = 2.32·10⁵), 274 (1.18·10⁵). MALDI-MS: m/z (%) = 548.3(100) [M + Na]⁺), 448.2(46), [M - Boc + Na]⁺), 348.2(10) [M - 2 Boc + Na]⁺).
4-Amino-5-[ N -( tert -butyloxycarbonyl)-(2′ R ,3′ S )-2′,3′-di( tert -butyloxycabonylamino)-(1′ S )-pyrrolidinyl]-2,6-dioxopyrimidine (10α/β). TLC: R _f = 0.29 (CH₂Cl₂-MeOH, 100:10). Mp 205 °C (decomp.). ¹H NMR (300 MHz, DMSO-d ₆, 100 °C): δ = 1.32-1.39 (s, 27 H, 9 × CH₃), 3.21 [dd, J = 9.7, 8.1 Hz, 1 H, H-C(4′)], 3.78 [m, 2 H, H-C(4′) and H-C(3′)], 4.19 [pseudo q, J _H-2 _′ _-H-1 _′ = J _H-2 _′ _-H-3 _′ = J _H-2 _′ _-NH = 8.0 Hz, 1 H, H-C(2′)], 4.36 [d, J = 7.1 Hz, 1 H, H-C(1′)], 5.75 (br s, 2 H, NH₂), 6.45 (br s, 1 H, 2 × NHBoc), 9.74, 9.83 (br s, 2 H, NH-1 and NH-3). ¹³C NMR (75 MHz, DMSO-d ₆, 100 °C): δ = 28.16 [q, (CH₃)₃C], 28.20 [q, (CH₃)₃C], 48.53 (t, C-4′), 49.88 (q, CH₃OH), 53.82 (d), 56.28 (d), 58.94 (d), 77.99 (s), 78.07(s), 78.23 (s), 84.73 (s), 149.65 (s), 152.17 (s), 153.07(s), 154.99 (s), 155.44 (s), 162.72 (s). UV (c = 5·10^-5 M in MeOH): λ_max = 268 (ε = 1.48·10⁵), 224 (ε = 5.01·10⁴). ESI-MS: m/z (%) = 549.3(96) [M + Na]⁺, 449.2(100) [M - Boc + Na]⁺, 349.2(38) [M - 2 Boc + Na]⁺). HR-MALDI: m/z calcd for C₂₃H₃₈N₆O₈Na: 549.2643; found: 549.2653. Anal. Calcd for C₂₃H₃₈N₆O₈·MeOH: C, 51.60; H, 7.57; N, 15.04. Found C, 51.50; H, 7.28; N, 14.86.
7-Carba-8-[ N -( tert -butyloxycarbonyl)-(2′ R ,3′ S )-2′,3′-di( tert -butyloxycabonylamino)-(1′ S )-pyrrolidi-nyl]guanine (11α/β).
Compound 11α: mp 225 °C (decomp.). ¹H NMR (300 MHz, DMSO-d ₆, 100 °C): δ = 1.30 (s, 9 H, 3 × CH₃), 1.35 (s, 9 H, 3 × CH₃), 1.40 (s, 9 H, 3 × CH₃), 3.21 [dd, J = 10.3, 8.0 Hz, 1 H, H-C(4′)], 3.80 [dd, J = 10.3, 7.6 Hz, 1 H, H-C(4′)], 3.93 [m, 1 H, H-C(3′)], 4.05 [pseudo q, J _H-1 _′ _-H-2 _′ = J _H-3 _′ _-H-2 _′ = J _H-2 _′ _-NH = 8.0 Hz, 1 H, H-C(2′)], 4.51 (d, J = 7.5, 1H, H-C(1′)], 5.77 (br s, 2 H, NH₂), 6.05 [d, J _H-7-NH-9 = 2.2 Hz, 1 H, H-C(7)], 8.35 (br d, J = 7.5 Hz, 1 H, NHBoc), 6.76 (br s, 1 H, NHBoc), 9.93 (br s, 1 H, NH-3), 10.41 (br s, 1 H, NH-9). ¹³C NMR (75 MHz, DMSO-d ₆, 100 °C): δ = 28.06 [q, (CH₃)₃C], 28.16 [q, (CH₃)₃C], 28.20 [q, (CH₃)₃C], 48.98 [t, C(4′)], 53.48 [d, C(3′)], 58.43 [d, C(1′)], 61.23 [d, C(2′)], 78.14 [s, (CH₃)₃C], 78.21 [s, (CH₃)₃C], 78.83 [s, (CH₃)₃C], 99.23 [d, C(7)], 99.86 [s, C(5)], 130.31 [s, C(8)], 150.97 [s, C(4)], 151.94 [s, C(2)], 153.43 (s, C=O of N-Boc), 154.93 (s, C=O of NHBoc-3′), 155.10 (s, C=O of NHBoc-2′), 158.29 [s, C(6)]. UV (c = 5·10^-5 M in MeOH): λ_max = 262 nm (ε = 1.55·10⁴), λ_min = 233 nm (ε = 3200), 216 (ε = 2.05·10⁴). MALDI-MS: m/z (%) = 572.3(100) [M + Na]⁺, 472.2(48), 432.2(60), 372.2(10), 227.1 (88), 151.1 (46). HR-MALDI: m/z calcd for C₂₅H₃₉N₇O₇Na: 572.2803; found: 572.2804. Anal. Calcd for C₂₅H₃₉N₇O₇: C, 54.63; H, 7.15; N, 17.84. Found: C, 54.58; H, 7.01; N, 17.87.
Preparation of Free C-Azanucleosides (Scheme 3). Representative Procedure for Step a: 2,4-Diamino-5-[ N -( tert -butyloxycarbonyl)-(2′ S ,3′ S )-2′,3′-dihydroxy-(1′ S )-pyrrolidinyl]-6-oxopyrimidine (12α).
The amount of 333 mg (0.62 mmol) of 4α was dissolved in 50 mL of sat. NH₃ in MeOH and stirred at r.t. for 24 h. TLC (CH₂Cl₂-MeOH, 8:1) showed the consumption of starting material 4α (R _f = 0.50) and the formation of a new UV active spot (R _f = 0.05). Evaporation of the solvent afforded a yellow oil residue that was purified by CC (silica gel, CH₂Cl₂-MeOH, 8:1). Fractions 29-41 (5 mL each) were combined and evaporated under reduced pressure at 30 °C to give 198 mg (98%) of 12α as white solid. TLC: R _f = 0.21 (CH₂Cl₂-MeOH, 4:1). ¹H NMR (300 MHz, DMSO-d ₆, 100 °C): δ = 1.30 (s, 9 H, 3 Me), 3.29 [dd, J = 11.2, 3.8 Hz, 1 H, H-C(4′)], 3.59 [dd, J = 10.8, 6.9 Hz, 1 H, H-C(4′)], 3.76, 3.93 [br s, 2 H, H-C(2′), H-C(3′)], 4.32 (d, J = 2.8 Hz, 1 H, H-1′), 4.81 (br s, 1 H, OH, exchanges with D₂O), 5.67 (br s, 2 H, NH₂, exchanges with D₂O), 5.91 (br s, 2 H, NH₂, exchanges with D₂O), 6.19 (br d, J = 7.5 Hz, 1 H, OH, exchanges with D₂O), 9.75 (br s, 1 H, OH). ¹³C NMR (75 MHz, DMSO-d ₆, 100 °C): δ = 28.08 (q), 52.96 (br t), 61.07 (d), 73.62 (d), 77.45 (s), 82.06 (br d), 87.41 (s), 153.08 (s), 153.37 (s), 162.61 (s), 162.53 (s). ESI-MS: m/z (%) = 676.9 (32) [2 M + Na]⁺, 366.0(20) [M + K]⁺), 350.0(100) [M + Na]⁺. UV (c = 5·10^-5 M in MeOH): λ_max = 274 nm (ε = 1.16·10⁴), 213 (ε = 2.24·10⁴), λ_min = 251 nm (ε = 3500).
4-Amino-5-[ N -( tert -butyloxycarbonyl)-(2′ S ,3′ S )-2′,3′-dihydroxy-(1′ S )-pyrrolidinyl]-2,6-dioxopyrimidine (14α).
TLC: R _f = 0.42 (CH₂Cl₂-MeOH, 4:1]. ¹H NMR (300 MHz, DMSO-d ₆, 100 °C): δ = 1.32 (s, 9 H, 3 Me), 3.29 [dd, J = 10.8, 5.1 Hz, 1 H, H-C(4′)], 3.57 [dd, J = 10.8, 6.3 Hz, 1 H, H-C(4′)], 3.80 (br s, 1 H, H-C(3′)], 4.01 [br s, 1 H, H-C(2′)], 4.32 [d, J = 3.9 Hz, 1 H,), 4.83 [br s, 1 H, HO-C(2′)], 5.46 [br s, 2 H, HO-C(3′)], 5.89 (br s, 2 H, NH₂, exchanges with D₂O), 9.85 (br s, 2 H, 2 NH). ¹³C NMR (75 MHz, DMSO-d ₆): δ = 28.11 (q), 51.66 [br t, C-(4′)], 58.91 [d, C-(1′)], 73.55 [d, C-(3′)], 77.74 (s, Me₃C), 80.11 [br d, C-(2′)], 84.97 [s, C-(5)], 150.05 (s), 152.48 (s), 153.53 (s), 163.42 (s). ESI-MS: m/z (%) = 679.0(8) [2 M + Na]⁺), 366.9(12) [M + K]⁺, 351.0(100) [M + Na]⁺). HR-MALDI: m/z calcd for C₁₃H₂₀N₄O₆Na [M + Na⁺]: 351.1275; found: 351.1272. UV (c = 5·10^-5 M in MeOH): λ_max = 269 nm (ε = 1.62·10⁴), 222 (ε = 5300), λ_min = 242 (ε = 3200), 215 (ε = 5220).
8-[ N -( tert -Butyloxycarbonyl)-(2′ S ,3′ S )-2′,3′-dihydroxy-(1′ S )-pyrrolidinyl]-7-carba-guanine (16α).
¹H NMR (600 MHz, DMSO-d ₆, 70 °C): δ = 1.31 (s, 9 H, 3 Me), 3.35 [dd, J = 3.2, 11.4 Hz, 1 H, H-C(4′)], 3.66 [dd, J = 5.5, 11.4 Hz, 1 H, H-C(4′)], 3.99 [br s, 1 H, H-C(2′), exchanges with D₂O), 4.00 (br s, 1 H, H-C(3′), exchanges with D₂O), 4.47 [br s, 1 H, H-C(1′)], 5.22 [d, J = 3.3 Hz, 1 H, HO-C(2′)], 5.39 [br s, 1 H, OH-C(3′)], 5.85 (br s, 2 H, NH₂), 6.05 [d, J = 1.8 Hz, 1 H, H-C(7)], 10.02 (br s, 1 H, NH), 10.22 (br s, 1 H, NH). ¹³C NMR (150.9 MHz, DMSO-d ₆, 70 °C): δ = 28.96 (q, Me), 53.47 [d, C(4′)], 63.50 [d, C(1′)], 75.13 [d, C(3′)], 79.37 (s, CMe₃), 81.58 [d, C(2′)], 100.71 [s, C(7)], 118.14, 13.05, 151.77 [s, C(4)], 153.07 [s, C(2)], 154.94 (s, C=O), 159.49 [s, C(6)]. ESI-MS (pos., MeOH): m/z (%) = 374 (10) [M + Na]⁺, 352 (40) [M + H]⁺. ESI-MS (neg., MeOH): m/z (%) = 386 (30) [M + Cl]^-), 350 (100) [M - H]^-.
8-[ N -( tert -Butyloxycarbonyl)-(2′ S ,3′ S )-2′,3′-dihydroxy-(1′ R )-pyrrolidinyl]-7-carba-guanine (16β).
TLC: R _f = 0.14 (CH₂Cl₂-MeOH, 8.5:1.5). ¹H NMR (600 MHz, DMSO-d ₆, 343 °K): δ = 1.26 (s, 9 H, Me), 3.22 [dd, J = 3.7, 11.0 Hz, 1 H, H-C(4′)], 3.67 [dd, J = 5.4, 11.0 Hz, 1 H, H-C(4′)], 3.93 [t, J = 5.1 Hz, 1 H, H-C(2′)], 4.00 [dd, J = 4.5 Hz, 1 H, 9.2, H-C(3′)], 4.75 [d, J = 5.9 Hz, 1 H, H-C(1′)], 5.77 (br s, 2 H, NH₂), 5.93 [s, 1 H, H-C(7)]. ¹³C NMR (150.9 MHz, DMSO-d ₆, measured at 343 K): δ = 28.92 (q, Me), 52.39 [t, C(4′)], 58.93 [d, C(1′)], 73.91 [d, C(3′)], 77.82 [d, C(2′)], 79.06 (s, CMe₃), 100.22 [d, C(7)], 100.86, 129.44, 151.78, 152.94, 155.03, 159.76. ESI-MS (pos., MeOH): m/z (%) = 374 (100) [M + Na]⁺), 352 (30) [M + H])⁺. ESI-MS (neg., MeOH): 386 (20) [M + Cl]^-, 350(100) [M - H]^-).
8-[ N -( tert -Butyloxycarbonyl)-(2′ S ,3′ S )-2′,3′-dihydroxy-(1′S)-pyrrolidinyl]-7-carba-xanthine (18α).
TLC: R _f = 0.47 (CH₂Cl₂-MeOH, 4:1). ¹H NMR (600 MHz, DMSO-d ₆, 70 °C): δ = 1.33 (s, 9 H, Me), 3.35 [d, J = 11.5 Hz, 1 H, H-C(4′)], 3.62 [dd, J = 4.8, 11.5 Hz, 1 H, H-C(4′)], 3.99 (s, 1 H), 4.03 (m, 1 H), 4.50 (s, 1 H), 5.29 (br s, 1 H, OH), 6.10 [s, 1 H, H-C(7)], 10.07 (br s, 1 H, NH). ¹³C NMR (150.9 MHz, DMSO-d ₆, 70 °C): d = 28.94 (q, Me), 53.83 [t, C(4′)], 63.50 [d, C(1′)], 79.64 [d, (C3′)], 98.81 [s, C(5)], 102.34 [d, C(7)], 130.42 [s, C(8)], 139.76 [s, C(4)], 151.47 [s, C(2)], 160.56 [s, H(C6)]. ESI-MS (positive, MeOH): m/z (%) = 727 (10) [2 M + Na]⁺), 705(2) [2 M + H]⁺), 398 (100) [M + 2 Na]⁺, 375 (40) [M + Na]⁺, 353 (40) [M + H]⁺). ESI-MS (neg., MeOH): m/z (%) = 387 (5) [M + Cl]^-, 351 (100) [M - H]^-.
8-[ N -( tert -Butyloxycarbonyl)-(2′ S ,3′)-2′,3′-dihydroxy-(1′ R )-pyrrolidinyl]-7-carba-xanthine (18β).
TLC: R _f = 0.39 (CH₂Cl₂-MeOH, 4:1). ¹H NMR (600 MHz, DMSO-d ₆, 70 °C): 1.27 (s, 9 H, Me), 3.26 [dd, J = 11.2 Hz, 1 H, 2.98, H-C(4′)], 3.61 [dd, J = 5.1, 11.2 Hz, 1 H, H-C(4′)], 3.94 (m, 1 H), 3.97 (s, 1 H), 4.75 (d, J = 5.4 Hz, 1 H), 5.02 (br s, 1 H, OH), 6.00 [s, 1 H, H-C(7)], 10.06 (br s, 1 H, NH), 10.35 (br s, OH, 0.5 H). ESI-MS (positive, MeOH): m/z (%) = 375 (10) [M + Na]⁺), 353 (5) [M + H]⁺). ESI-MS (neg., MeOH): m/z (%) = 387(50) [M + Cl]^-, 351 (100) [M - H]^-.
Representative Procedure for Step b: 2,4-Diamino-5-[(2′ S ,3′ S )-2′,3′-dihydroxy-(1′ S )-pyrrolidinyl]-6-oxo-pyrimidine Hydrochloride (13α) . The amount of 151 mg (0.46 mmol) of 12α was suspended in 50 mL of sat. HCl in Et₂O and stirred at r.t. for 2 h. The off white solid in the reaction mixture was filtered, washed with 20 mL Et₂O and dried to give 113 mg (83%, calcd according to 2HCl salt) of 13α as white solid. ¹H NMR (300 MHz, CD₃OD): δ = 3.35 [dd, J = 4.5, 12.2 Hz, 1 H, H-C(4′)], 3.53 [dd, J = 5.6, 12.2 Hz, 1 H, H-C(4′)], 4.25 [ddd, J _cis-H-4 _′ _-H-3 _′ = 5.6 Hz, J _trans-H-4 _′ _-H-3 _′ = J _H-2 _′ _-H-3 _′ = 4.2 Hz, 1 H, H-C(3′)], 4.44 [dd, J = 3.5, 7.5 Hz, 1 H, H-C(2′)], 4.55 [d, J = 7.5 Hz, 1 H, H-C(1′)]. ¹³C NMR (75 MHz, DMSO-d ₆): δ = 48.30 (t), 57.95 (d), 74.01(d), 76.49 (d), 80.38 (s), 151.88 (s), 155.47 (s), 160.75 (s). ESI-MS: m/z (%) = 228.0(100) [M + H]⁺). HR-MALDI: m/z calcd for C₈H₁₄N₅O₃ [M + H]⁺: 228.1091; found: 228.1089.
4-Amino-5-[(2′ S ,3′ S )-2′,3′-dihydroxy-(1′ S )-pyrrolidinyl]-2,6-dioxopyrimidine Hydrochloride (15α).
¹H NMR (300 MHz, DMSO-d ₆): δ = 3.08 [d, J = 5.1 Hz, 1 H, H-C(4′)], 3.24 [dd, J = 6.3, 11.7 Hz, 1 H, H-C(4′)], 3.98 [d, J = 4.8 Hz, 1 H, H-C(1′)], 4.28 (m, 2 H, H-2′ and H-3′), 5.69 (br s, 2 H, NH₂), 7.01 (br s, 2 H, NH₂), 8.45 (br s, 1 H, OH), 9.56 (br s, 1 H, OH), 10.71, 10.72 (s, 2 H, NH). ¹³C NMR (75 MHz, DMSO-d ₆): δ = 48.16 (t), 58.16 (d), 73.99 (d), 76.48 (d), 77.44 (s), 149.34 (s), 154.42 (s), 164.00 (s). ESI-MS: 229.0(100) [M + H]⁺). HR-MALDI: m/z calcd for C₈H₁₄N₅O₃ [M + H]⁺: 229.0937; found: 229.0927.
8-[(2′ S ,3′)-2′,3′-Dihydroxy-(1′ S )-pyrrolidinyl]-7-carba-guanine Hydrochloride (17α).
TLC: R _f = 0.08 (CH₂Cl₂-MeOH, 8:2). ¹H NMR (600 MHz, DMSO-d ₆): δ = 3.15-3.17 [br m, 1 H, H-C(4′)], 3.40 [m, 1 H, H-C(4′)], 4.14 (dd, J = 3.5, 7.3 Hz, 1 H, H-C(3′)], 4.24 [t, J = 4.0 Hz, 1 H, H-C(2′)], 4.36 [dd, J = 6.0, 11.5 Hz, 1 H, H-C(1′)], 6.49 [s, 1 H, H-C(7)], 9.15 (br s, 1 H, -NH), 10.02 (br s, 1 H, -NH), 10.73 (br s, 1 H, -NH), 11.21 (br s, 1 H, -NH). ¹³C NMR (150.9 MHz, DMSO-d ₆): δ = 41.35 [d, C(4′)], 61.64 [d, C(1′)], 74.96 [d, C(3′)], 79.84 [d, C(2′)], 101.01 [s, C(5)], 104.81 [d, C(7)], 125.0 [s, C(8)], 152.91 [s, C(2)], 158.21 [s, C(6)] (one carbon signal is not observable). ESI-MS (pos., MeOH): m/z (%) = 503 (20) [2 M + H]⁺), 252 (100) [M + H]⁺). ESI-MS (neg., MeOH): m/z (%) = 537 (10) [2 M + Cl]^-, 286 (50) [M + Cl]^-), 250 (100) [M - H]^-.
8-[(2′ S ,3′ S )-2′,3′-Dihydroxy-(1′ R )-pyrrolidinyl]-7-carba-guanine Hydrochloride (17β).
TLC: R _f = 0.08 (CH₂Cl₂-MeOH, 8:2). ¹H NMR (600 MHz, DMSO-d ₆): δ = 3.01-3.04 (br m, 1 H, H-4′), 3.53-3.57 [m, 1 H, H-C(4′)], 4.08 [br s, H-C(2′)], 4.24 [d, J = 4.3 Hz, 1 H, H-C(3′)], 4.70 [dd, J = 2.5, 8.7 Hz, 1 H, H-C(1′)], 6.59 (d, J = 1.9 Hz, 1 H, H-C(7)], 9.24 (br s, 1 H, NH), 10.38 (br s, 1 H, NH), 11.48 (br s, 1 H, NH), 11.56 (br s, 1 H, -NH). ¹³C NMR (150.9 MHz, DMSO-d ₆): δ = 51.32 [d, C(4′)], 58.46 [d, C(1′)], 74.92 [d, C(2′)], 76.79 [d, C(3′)], 100.98 [d, C(5)], 105.35 [d, C(7)], 122.56 [d, C(8)], 152.64 [s, C(2)], 157.97 [d, C(6)] (one carbon-signal not observable). ESI-MS (pos., MeOH): δ = 503(10) [2 M + H]⁺, 252 (100) [M + H]⁺). EI-MS (neg., MeOH): δ = 537 (10) [2 M + Cl]^-, 286 (40) [M + Cl]^-, 250 (100) [M - H]^-.
8-[(2′ S ,3′ S )-2′,3′-Dihydroxy-(1′ S )-pyrrolidinyl]-7-carba-xanthine Hydrochloride (19α).
TLC: R _f = 0.56 (CH₂Cl₂-MeOH-aq NH₃, 5:5:0.5). ¹H NMR (600 MHz, DMSO-d ₆): δ = 3.43 [dd, J = 11.95, 5.06 Hz, 1 H, H-C(4′)], 4.19 [m, 1 H, H-C(3′)], 4.23 [m, 1 H, H-C(2′)], 4.45 [d, J = 4.32 Hz, 1 H, H-C(1′)], 6.48 [s, 1 H, H-C(7)], 9.11 (br s, 0.5 H, NH), 9.94 (br s, 0.5 H, NH), 10.27 (br s, 1 H, OH,), 10.86 (br s, 1 H, OH), 11.30 (br s, 0.6 H, NH). ¹³C NMR (150.9 MHz, DMSO-d ₆): δ = 50.93, 62.43, 75.26, 79.93, 99.54, 105.78, 123.71, 140.91, 151.52, 160.39. ESI-MS (pos., MeOH): m/z (%) = 275 (10) [M + Na]⁺), 253 (100) [M + H]⁺). ESI-MS (neg., MeOH): m/z (%) = 287 (5) [M + Cl]^-, 251 (10) [M - H]^-.
Preparation of Free C-Azanucleosides (Scheme 4). Representative Procedure. 2,4-Diamino-5-[(2′ R ,3′)-2′,3′-diamino-(1′ S )-pyrrolidinyl]-6-oxopyrimidine Hydrochloride (20α). The amount of 132 mg (0.25 mmol) of 9α was suspended in 20 mL of sat. HCl in Et₂O and stirred at r.t. for 2 h. The off white solid in the reaction mixture was filtered, washed with 20 mL Et₂O and dried to give 85 mg of 20α (91%, calcd according to 4HCl salt) as white solid. ¹H NMR (300 MHz, CD₃COOD-D₂O, 5:2): δ = 4.01 [dd, J = 4.7, 13.7 Hz, 1 H, H-C(4′)], 4.23 [dd, J = 8.1, 13.7 Hz, 1 H, H-C(4′)], 4.67 [ddd, J = 8.0, 5.0, 5.0 Hz, 1 H, H-C(3′)], 4.90 (dd, J = 5.6, 7.5 Hz, 1 H, H-2′), 5.20 [d, J = 7.8 Hz, 1 H, H-C(1′)]. ¹³C NMR (75 MHz, DMSO-d ₆): 44.54, 50.11, 51.98, 55.07, 76.86, 156.56, 157.12, 161.06. ESI-MS (MeOH): m/e (%) = 226.1 (100) [M + H⁺], 450.9 (13) [2 M + H⁺].
4-Amino-5-[(2′ R ,3′)-2′,3′-diamino-(1′ S )-pyrrolidinyl]-2,6-dioxopyrimidine Hydrochloride (21α).
¹H NMR (300 MHz, CD₃COOD-D₂O, 2:1; contaminated with 6% of the corresponding β-epimer): δ = 4.02 [dd, J = 4.6, 13.4 Hz, 1 H, H-C(4′)], 4.24 [dd, J = 8.1, 13.4 Hz, 1 H, H-C(4′)], 4.67 (ddd, J = 8.1, 5.2, 5.2 Hz, 1 H, H-3′), 4.89 [dd, J = 5.6, 8.1 Hz, 1 H, H-C(2′)], 5.14 (d, J = 7.8 Hz, 1 H, H-1′). ¹³C NMR (75 MHz, DMSO-d ₆-D₂O): 47.67, 53.19, 55.68, 58.87, 77.07, 152.46, 156.82, 166.30. ESI-MS (MeOH): m/e (%) = 227.1 (100) [M + H⁺], 453.0 (32) [2 M + H⁺].
7-Carba-8-[(2′ R ,3′ S )-2′,3′-diamino-(1′ S )-pyrrolidi-nyl]guanine Hydrochloride (22α).
¹H NMR (400 MHz, D₂O): δ = 3.60 [dd, J = 7.3, 13.4 Hz, 1 H, H-C(4′)], 3.97 [dd, J = 9.1, 13.4 Hz, 1 H, H-C(4′)], 4.35 [ddd, J _trans-H-4 _′-H-3 _′ = 7.3 Hz, J _cic _-H-4 _′-H-3 _′ = 9.1 Hz, J _H-2 _′-H-3 _′ = 8.3 Hz, 1 H, H-C(3′)], 4.50 [dd, J = 8.3, 10.4 Hz, 1 H, H-C(2′)], 5.03 (d, J = 10.5 Hz, 1 H, H-1′), 5.03 [d, J = 0.5 Hz, 1 H, H-C(7)]. ¹³C NMR (100 MHz, D₂O): δ = 45.29 [t, C(4′)], 50.49 [d, C(3′)], 54.95 [d, C(2′)], 56.82 [d, C(1′)], 101.00 [s, C(5)], 106.65 [d, C(7)], 119.59 [s, C(8)], 145.08 (s), 151.99 (s), 160.01 (s). ESI-MS (MeOH): m/e (%) = 250.2 (20) [M + H⁺], 499.3 (37) [2 M + H⁺], 537.3 (100) [2 M + K⁺].