Structurally Modified Flavins
acetic acid (3 mL) was stirred at room temp. for 6 h. Water
(100 mL) was added, the resulting mixture was adjusted to pH 7
with aqueous NH3 and then extracted with ethyl acetate
(2ϫ50 mL). The aqueous phase was evaporated under vacuum,
absolute ethanol was added to form the ethyl ester of boric acid,
and the mixture was evaporated. The last step was repeated five
times until the white crystals stopped appearing. Gel filtration of
the residue and HPLC (A:B, 90:10, retention time 9 min) furnished
tic acid (0.75 mL) in the dark. The mixture was stirred at room
temp. for 3 h, and then 0.5 mL of water was added. The suspension
was quenched for an additional 3 h before the solvents were re-
moved under reduced pressure. The crude orange solid was washed
with water (2ϫ0.5 mL), and dried. FC on silica gel, eluting with
DCM/MeOH (97:3) furnished 24 (50 mg, 80%). 1H NMR
(400 MHz, CD3OD): δ = 8.17 (s, 1 H, 6-CH), 7.72 (s, 1 H, 9-CH),
5.69 (m, 1 H, 2Ј-CH), 5.53 (t, J = 6 Hz, 1 H, 3Ј-CH), 5.40 (m, 1
H, 4Ј-CH), 5.18 (m, 2 H, 5Ј-CH2), 4.45 (dd, J = 12, 3 Hz, 1 H, 1Ј-
CHH), 4.26 (dd, J = 12, 6 Hz, 1 H, 1Ј-CHH), 3.35 (m, 1 H, iPr-
1
6 (135 mg, 73%). H NMR (400 MHz, [D6]DMSO): δ = 11.41 (m,
1 H, 3-NH), 8.11 (d, J = 8 Hz, 1 H, C-6), 8.07 (d, J = 8 Hz, 1 H,
C-9), 7.90 (t, J = 8 Hz, 1 H, C-8), 7.63 (t, J = 8 Hz, 1 H, C-7), 5.09 CH), 2.50 (s, 3 H, CH3), 2.18, 2.16, 2.00, 1.70 (4s, 12 H, 4ϫCH3-
(d, J = 6 Hz, 1 H, OH), 4.89 (m, 1 H, 2Ј-CH), 4.83 (d, J = 6 Hz, Ac), 1.38, 1.36 (2s, 6 H, 2ϫCH3-iPr) ppm. 13C NMR (100 MHz,
1 H, OH), 4.79 (d, J = 6 Hz, 1 H, OH), 4.68 (d, J = 14 Hz, 1 H, CD3OD): δ = 172.3, 171.8, 171.5, 171.3 (4ϫCO-Ac), 158.8 (C-4),
3Ј-CH), 4.45 (t, J = 6 Hz, 1 H, OH), 4.24 (m, 1 H, 4Ј-CH), 3.75
157.1 (C-2), 155.0 (C-10a), 137.3 (C-8), 134.6 (C-7), 134.2 (C-4a),
(m, 4 H, 5Ј-CH2, 1Ј-CH2) ppm. 13C NMR (100 MHz, [D6]DMSO): 126.0 (C-5a), 122.5 (C-6), 114.8 (C-9), 71.4 (C-3Ј), 70.8 (C-4Ј), 70.6
δ = 159.8 (C-4), 155.6 (C-2), 151.2 (C-10a), 138.2 (C-9a), 135.1 (C-
4a), 134.6 (C-8), 133.9 (C-5a), 131.5 (C-6), 126.0 (C-7), 117.8 (C-
(C-2Ј), 63.0 (C-5Ј), 45.4 (C-1Ј), 31.7 (iPr-CH), 23.33, 23.30 (2ϫiPr-
CH3), 21.0, 20.8, 20.60, 20.57 (4ϫCH3-Ac), 19.2 (CH3) ppm. EI
9), 73.7 (C-3Ј), 72.7 (C-4Ј), 68.8 (C-2Ј), 63.4 (C-5Ј), 47.6 (C-1Ј) MS: m/z = 588 [M], 545 [M – Ac], 529 [M – OAc], 286 [M – ribityl],
ppm. ESI MS: m/z = 371 [M + Na]+, 349 [M + H]+, 348 [M].
270 [M – ribityl – O]. HRMS: calcd. for C27H32N4O11Na
HRMS: calcd. for C15H16N4O6Na 371.096206 [M + Na]+; found 611.195981 [M + Na]; found 611.196507.
371.096420.
Tetra-O-acetyl-8-isopropylriboflavin: Na2S2O4 (27 mg, 1.5 equiv.) in
3-Isopropyl-4-methylriboaniline (22): Riboaniline 22 was prepared
from 2-isopropyl-3-methylaniline 21 with 79% yield as described
for 19. Reaction time: 72 h. 1H NMR (400 MHz, CD3OD), δ =
6.87 (d, J = 8 Hz, 1 H, 5-CH), 6.63 (d, J = 4 Hz, 1 H, 2-CH), 6.45
(dd, J = 8, 2 Hz, 1 H, 6-CH), 3.91 (m, 1 H, 2Ј-CH), 3.76 (m, 2 H,
3Ј-CH, 4Ј-CH), 3.63 (m, 2 H, 5Ј-CH2), 3.44 (dd, J = 12, 3 Hz, 1
H, 1Ј-CHH), 3.30 (m, 4 OH), 3.08 (m, 2 H, iPr-CH, 1Ј-CHH), 2.18
(s, 3 H, CH3), 1.19, 1.17 (2s, 2ϫiPr-CH3) ppm. 13C NMR
(100 MHz, CD3OD), δ = 148.5, 148.4 131.7, 125.2, 112.2, 112.1
(6ϫC-Ar), 74.9 (C-3Ј), 74.3 (C-4Ј), 72.1 (C-2Ј), 64.6 (C-5Ј), 48.1
(C-1Ј), 30.5 (iPr-CH), 23.6 (2ϫiPr-CH3), 18.5 (CH3) ppm. EI MS:
m/z = 283 [M], 162 [M – (CHOH)3CH2OH].
water (3 mL) was added to a solution of 24 (50 mg, 0.085 mmol)
in EtOH (3 mL) under argon. After stirring at room temp. for 4 h,
the solvents were evaporated, and the crude yellow solid was
washed with water (2ϫ2 mL) and dried under vacuum. FC on sil-
ica gel eluting with DCM/MeOH (98:2) yielded the acetylated iso-
1
propylriboflavin (49 mg, 100%). H NMR (400 MHz, CD3OD), δ
(ppm): 7.95 (s, 1 H, 6-CH), 7.75 (s, 1 H, 9-CH), 5.71 (q, J = 4 Hz,
1 H, 2Ј-CH), 5.54 (dd, J = 6, 4 Hz, 1 H, 3Ј-CH), 5.41 (m, 1 H, 4Ј-
CH), 5.11 (m, 2 H, 5Ј-CH2), 4.46 (dd, J = 12, 3 Hz, 1 H, 1Ј-CHH),
4.24 (dd, J = 12, 6 Hz, 1 H, 1Ј-CHH), 3.41 (q, J = 7 Hz, 1 H, iPr-
CH), 2.52 (CH3), 2.18, 2.17, 2.01, 1.64 (4s, 12 H, 4ϫCH3-Ac), 1.39
(m, 6 H, 2ϫCH3-iPr) ppm. 13C NMR (100 MHz, CD3OD): δ =
172.3, 171.9, 171.37, 171.27 (4ϫCO-Ac), 162.1 (C-4), 159.0 (C-2),
152.4 (C-10a), 137.9 (C-8), 137.2 (C-7), 135.6 (C-4a), 133.6 (2 C,
C-5a, C-6), 113.6 (C-9), 71.4 (C-3Ј), 70.8 (C-4Ј), 70.3 (C-2Ј), 63.0
(C-5Ј), 45.4 (C-1Ј), 31.9 (iPr-CH), 23.5, 23.4 (2ϫiPr-CH3), 21.0,
20.7, 20.6, 20.4 (4ϫCH3-Ac), 18.9 (CH3) ppm. EI MS: m/z = 572
[M], 529 [M – Ac], 513 [M – OAc], 284 [M – (CHOAc)3CH2OAc],
270 [M – ribityl]. HRMS: calcd. for C27H32N4O10Na 595.201063
[M + Na]; found 595.201277.
Intermediate 23: Ribitylated aniline 22 (200 mg, 0.70 mmol) and 6-
chlorouracil (125 mg, 1.2 equiv.), pre-dried together with powdered
malonitrile (40 mg), were suspended in dry methanol (5 mL) and
stirred under reflux for 3 d. The solvent was removed under re-
duced pressure, and the resulting solid was dissolved in a mixture
of pyridine (4 mL) and acetic anhydride (0.4 mL). The resulting
mixture was allowed to stir at room temp. for 6 h. The solvent was
removed under reduced pressure with toluene, and the resulting
residue was dissolved in DCM (50 mL) and washed with water
(3ϫ20 mL) and brine (20 mL). The organic extracts were dried
with MgSO4, filtered, and the solvent was removed under reduced
pressure. FC on silica gel, eluting with DCM/MeOH (95:5), af-
8-Isopropylriboflavin (7): Tetra-O-acetyl-8-isopropylriboflavin
(50 mg, 0.09 mmol) was dissolved in methanol saturated with NH3
(2.5 mL), and the resulting mixture was stirred at room temp. for
5 h. The solvent was removed under reduced pressure, and the
crude solid was washed with a mixture of DCM/MeOH (4:1,
0.5 mL) to remove acetylated byproducts. The resulting solid was
then dissolved in 5% aqueous NH4OH (5 mL), filtered, and lyophi-
lized. Pure 7 (28 mg) was obtained in 80% yield. 1H NMR
(400 MHz, [D6]DMSO): δ = 11.33 (br. s, 1 H, 3-NH), 7.91 (s, 1 H,
6-CH), 7.89 (s, 1 H, 9-CH), 5.15 (m, 1 H, OH), 5.03 (m, 1 H, 2Ј-
CH), 4.78 (m, 2 H, 2 OH), 4.63 (d, J = 12 Hz, 1 H, 3Ј-CH), 4.46
(t, J = 6 Hz, 1 H, OH), 4.21 (m, 1 H, 4Ј-CH), 3.63 (m, 4 H, 5Ј-
CH2, 1Ј-CH2), 3.20 (m, partially obscured by the solvent signal, 1
H, iPr-CH), 2.47 (s, 3 H, CH3), 1.28 (m, 6 H, 2ϫCH3-iPr) ppm.
13C NMR (100 MHz, [D6]DMSO): δ = 160.0 (C-4), 155.8 (C-2),
155.6 (C-10a), 151.1 (C-9a), 137.1 (C-8), 134.2 (C-7), 133.7 (C-4a),
132.3 (C-5a), 131.5 (C-6), 113.6 (C-9), 73.5 (C-3Ј), 72.7 (C-4Ј), 69.0
(C-2Ј), 63.2 (C-5Ј), 47.1 (C-1Ј), 30.0 (iPr-CH), 23.0, 22.7 (2ϫiPr-
CH3), 18.4 (CH3) ppm. EI MS: m/z = 404 [M], 388 [M – O], 284
[M – (CHOH)3CH2OH], 270 [M – ribityl]. HRMS: calcd. for
C19H25N4O6 405.176856 [M + H]; found 405.176635.
1
forded the desired product, 23 (297 mg, 75% after two steps). H
NMR (400 MHz, CDCl3), δ = 7.18 (m, 1 H, 5α-CH), 7.01 (m, 1
H, 6-CH), 6.89 (m, 1 H, 9-CH), 5.30 (m, 1 H, OH), 5.21 (m, 1 H,
OH), 5.08 (m, 1 H, OH), 4.92 (m, 1 H, OH), 4.22 (m, 2 H, 2Ј-CH,
3Ј-CH), 4.02 (m, 1 H, 4Ј-CH), 3.88 (m, 1 H, 5Ј-CHH), 3.66 (m, 1
H, 5Ј-CHH), 3.41 (m, 2 H, 1Ј-CH2), 3.09 (q, J = 7 Hz, 1 H, iPr-
CH), 2.32 (s, 3 H, CH3), 2.06, 2.00, 1.97, 1.83 (4s, 12 H, 4ϫAc-
CH3), 1.18 (m, 6 H, 2ϫiPr-CH3) ppm. 13C NMR (100 MHz,
CDCl3), signals which could be interpreted: δ = 170.5, 170.0, 169.6,
169.5 (4ϫCO-Ac), 164.9 (C-4), 153.8 (C-2), 150.4 (C-10a), 150.3
(C-8), 148.7 (C-9a), 142.1 (C-7), 137.2 (C-5a), 137.0 (C-6), 132.5
(C-9), 74.6 (C-4a), 72.8 (C-3Ј), 71.1 (C-4Ј), 70.1 (C-2Ј), 66.2 (C-5Ј),
51.9 (C-1Ј), 29.6 (iPr-CH), 23.0, 22.9 (2ϫCH3-iPr), 20.9, 20.7,
20.6, 20.5 (4ϫCH3-Ac), 18.9 (CH3) ppm. EI MS: m/z = 561 [M],
502 [M – OAc], 442 [M – 2OAc], 259 [M – ribityl].
Tetra-O-acetyl-8-isopropyl-5-nitrosoriboflavin (24): NaNO2 (58 mg,
0.5 mmol) was added to a solution of 23 (58 mg, 0.1 mmol) in ace-
Eur. J. Org. Chem. 2008, 5401–5406
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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