A new and improved N-3 alkylation of 10-substituted isoalloxazines using 1,8-diazabicyclo[5.4.0]undec-7-ene in benzene

Article abstract of DOI:10.1081/SCC-120015816

1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) has been identified as a remarkable base for the alkylation at N-3 position of 10-substituted isoalloxazines with alkyl halides in dry benzene.

Full text of DOI:10.1081/SCC-120015816

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A New and Improved N -3 Alkylation of 10-Substituted
Isoalloxazines Using 1,8-Diazabicyclo[5.4.0]undec-7-
ene in Benzene
Geetanjali a , Ram Singh a & S. M. S. Chauhan a
a Department of Chemistry , University of Delhi , Delhi, India
Published online: 16 Aug 2006.
To cite this article: Geetanjali , Ram Singh & S. M. S. Chauhan (2003) A New and Improved N -3 Alkylation of 10-Substituted
Isoalloxazines Using 1,8-Diazabicyclo[5.4.0]undec-7-ene in Benzene, Synthetic Communications: An International Journal for
Rapid Communication of Synthetic Organic Chemistry, 33:4, 613-620, DOI: 10.1081/SCC-120015816
To link to this article: http://dx.doi.org/10.1081/SCC-120015816
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SYNTHETIC COMMUNICATIONSÕ
Vol. 33, No. 4, pp. 613–620, 2003
A New and Improved N-3 Alkylation of
10-Substituted Isoalloxazines Using
1,8-Diazabicyclo[5.4.0]undec-7-ene in Benzene
*
Geetanjali,Ram Singh,and S. M. S. Chauhan
Department of Chemistry, University of Delhi,
Delhi, India
ABSTRACT
1,8-Diazabicyclo[5.4.0]undec-7-ene (DBU) has been identified as a
remarkable base for the alkylation at N-3 position of 10-substituted
isoalloxazines with alkyl halides in dry benzene.
The flavin (isoalloxazine) cofactors FAD (flavin adenine dinucleo-
tide) and FMN (flavin mononucleotide) are involved in a huge variety
of biological transformations and electron transfer processes.[1–3]
The diverse and vital process mediated by flavin cofactors has made
structural analogs the focus of coenzyme inhibitor design and synthesis.[4]
*Correspondence: S. M. S. Chauhan, Department of Chemistry, University of
Delhi, Delhi 7, India; E-mail: smschauhan@chemistry.du.ac.in.
613
DOI: 10.1081/SCC-120015816
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614
Geetanjali,Singh,and Chauhan
The isoalloxazine derivatives have been widely used in our research[5,6]
and others[7,8] as synthetic models for flavoenzyme processes.
A wide variety of N-3 alkylisoalloxazines have been synthesized via a
number of routes.[9–11] Some of these methods are restricted to methyl
substitution,[9] slow reaction rate,[10] low yields[11] and use of excess alky-
lating agents. In this article, we report an alternative simple procedure for
the N-3 alkylation of 10-substituted isoalloxazines using DBU as a base.
Bicyclic amidine, DBU is a non-nucleophilic base and has been used in a
variety of organic reactions including esterification, condensation, cycli-
zation, alkylation of active methylene compounds, etc.[12] The application
of DBU in the alkylation of cyclic amide nitrogens as present at N-3
position of isoalloxazines is not reported so far.
RESULTS AND DISCUSSION
The reaction of 10-methylisoalloxazine with methyl iodide and DBU
in dry benzene at room temperature for 1 h afforded 3,10-dimethyliso-
alloxazine in 97% yield (Table 1, Entry 1, Sch. 1). After the reaction, the
DBU–hydroiodide (DBU–HI) complex was washed out with water from
the reaction mixture. The product was purified by recrystallization
(petroleumether–benzene). The product was characterized by various
spectroscopic data including UV–visible, IR, 1H NMR, mass spectroscopy
and elemental analysis. Similarly, the other isoalloxazines were also alky-
lated at N-3 position and characterized. The results of our synthetic study
(Table 1) show that the reaction conditions afford high yields (87–97%) of
the desired products. The required 10-substituted isoalloxazines were
prepared according to the known literature procedure.[6,13]
N-3 Alkylation of isoalloxazines had been done by various
methods[9–11] but the present procedure has some advantages over the
conventional methods. First, a wide variety of N-3 alkylated isoalloxa-
zines can be prepared under mild conditions. Secondly, the procedure is
simple and easily scaled up. Thirdly, the reaction proceeds in non-polar
solvent, making the work up very simple, products can be obtained in
most of the cases in sufficiently pure form only by removal of DBU–HX.
The process also avoids the use of excess alkyl halides.
The reaction of isoalloxazines with alkyl halides in the presence of
usual base i.e., anhydrous K2CO3 is too slow to be used for the
alkylation.[10] For example, the reaction of 10-butylisoalloxazine with
hexadecylbromide and DBU in dry benzene at room temperature for
2.5 h afforded 3-hexadecyl-10-butylisoalloxazine in 90% yield (Entry 3),

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N-3 Alkylation of 10-Substituted Isoalloxazines
Table 1. 3,10-Disubstituted isoalloxazines prepared.
615
Reaction Yield M.p. (lit. m.p.)Ref
time (h) (%)
(ꢁC)
Entry
R
R0X
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
CH3
CH3I
CH3I
CH3(CH2)14CH2Br
CH3I
CH3(CH2)2CH2Br
CH3(CH2)4CH2Br
CH3(CH2)10CH2Br
CH2¼CH2CH2Br
C6H5CH2Br
CH3I
1.0
1.0
2.5
1.0
1.5
1.5
2.0
2.0
2.0
1.0
1.0
1.0
1.5
1.5
2.0
2.5
1.0
1.0
1.5
1.0
1.0
1.0
1.0
1.0
97 304–305 (302–304)[14]
(CH2)3CH3
(CH2)3CH3
(CH2)5CH3
(CH2)5CH3
(CH2)5CH3
(CH2)5CH3
(CH2)5CH3
(CH2)5CH3
(CH2)9CH3
(CH2)11CH3
(CH2)15CH3
(CH2)15CH3
(CH2)15CH3
(CH2)15CH3
(CH2)15CH3
(CH2)17CH3
C6H5
95
90
96
94
90
89
89
87
92
94
96
93
93
89
88
91
93
90
90
89
91
93
89
307–308 (308)[15]
77–78 (77–80)[10]
180 (180)[16]
153
106
98–99
121
182
156 (155)[16]
177 (177–179)[16]
140 (140)[16]
130
CH3I
CH3I
CH3(CH2)2CH2Br
CH3(CH2)4CH2Br
CH3(CH2)10CH2Br
CH3(CH2)14CH2Br
CH3I
111
104
95
157 (156–157)[16]
>300 (>300)[9]
>300
CH3I
CH3CH2Br
C6H5
20-CH3C6H4 CH3I
20,60-CH3C6H3 CH3I
>330 (>360)[17]
295 (297–299)[14]
>300 (>300)[9]
>330 (353–355)[17]
282 (284)[9]
40-ClC6H4
CH3I
40-OCH3C6H4 CH3I
C6H5CH2 CH3I
Scheme 1.
whereas the same reaction in the presence of anhydrous potassium car-
bonate under similar condition gave no product. The above reaction in
anhydrous K2CO3/DMF gave 61% yield after two days.[10] High tem-
perature (ꢀ100ꢁC) and the long reaction time are usually required for the

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616
Geetanjali,Singh,and Chauhan
synthesis of N-3 alkylisoalloxazines by means of alkyl halides and anhy-
drous K2CO3. Special care has to taken with methyl iodide i.e., moderate
temperature with continuous circulation of cold water as methyl iodide is
low boiling, whereas these conditions can be avoided using DBU as base.
In conclusion, our conditions for the N-3 alkylation of isoalloxazines
are among the mildest available. DBU can be used as a base for alkyla-
tion of various N-10 alkyl/aryl-isoalloxazines and the reaction proceeds
smoothly in a non-polar solvent at room temperature. Hence, the above
procedure for the N-3 alkylation of isoalloxazines is superior to those
methods as mentioned earlier.
EXPERIMENTAL
DBU and alkyl halides were obtained fromFluka, Switzerland and
were used as such. All melting points were determined on Thomas
Hoover Unimelt Capillary Apparatus and are uncorrected. IR spectra
were recorded on Shimadzu TR-435 spectrometer (ꢀmax in cmÀ1).
Absorption spectra were recoreded on Shimadzu UV-260 spectrophotom-
eter and absorption maxima were expressed in nm. 1H NMR was
recorded on Bruker Avance-300 spectrometer using TMS as an internal
reference (chemical shift in ppm).
General Procedure for the N-3 Alkylation of
10-Substituted Isoalloxazines
DBU (0.5 mmol) was added to a solution of alkyl halide (0.6 mmol)
and isoalloxazine (0.5 mmol) in dry benzene (50 mL). The reaction mix-
ture was stirred at roomtemperature for the period given in Table 1 and
washed with water. The organic layer was dried over anhydrous sodium
sulphate and the solvent was removed under reduced pressure. The resi-
due was further washed with petroleumether to remove the alkylating
agent, if present and recrystallized frompetroleumether–benzene. In a
few cases where starting materials was present, the residue was chroma-
tographed over silica gel (60–120 mesh) using chloroform as an eluent.
3-Butyl-10-hexylisoalloxazine (5): UV–visible (CHCl3), ꢁmax ("max
,
mM): 273 (29.27), 333 (6.92), 417 (6.32), 443 (7.56), 465 (5.17);
1H NMR (CDCl3): 8.27 (dd, 1H, 6-H, J ¼ 1.8 and 8.2 Hz), 7.91 (t, 1H,
7-H), 7.59 (t, 1H, 8-H), 6.90 (d, 1H, 9-H, J ¼ 8.1 Hz), 4.41 (t, 2H,
N10–CH2), 3.55 (t, 2H, N3–CH2), 1.60–1.23 (m, 12H, 6 Â CH2), 0.90 (t,

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N-3 Alkylation of 10-Substituted Isoalloxazines
617
6H, 2 Â CH3); IR (KBr): 2925, 2856, 2362, 1708, 1658, 1612, 1587, 1552,
1515, 1461, 1363, 1278, 1185, 806, 767, 720; MS m/z (% base): 354 (Mþ,
97), 324 (10), 298 (16), 283 (85), 269 (49), 227 (72), 214 (100), 197 (20),
171 (37), 170 (71), 143 (30), 55 (29) and 43 (94); Anal. calcd.
for C20H26N4O2: C, 67.77; H, 7.39; N, 15.81. Found: C, 67.72; H, 7.35;
N, 15.78.
3,10-Dihexylisoalloxazine (6): UV–visible (CHCl3), ꢁmax ("max, m M):
266 (12.31), 333 (4.27), 422 (2.81), 443 (4.42), 472 (3.33); 1H NMR
(CDCl3): 8.32 (dd, 1H, 6-H, J ¼ 1.6 and 8.6 Hz), 7.90 (t, 1H, 7-H),
7.64–7.59 (m, 2H, 8-H and 9-H), 4.68 (t, 2H, N10–CH2), 3.50 (t, 2H,
N3–CH2), 1.36–1.25 (m, 16H, 8 Â CH2), 0.93–0.86 (m, 6H, 2 Â CH3);
IR (KBr): 2927, 2858, 2362, 1707, 1650, 1604, 1590, 1502, 1459, 1350,
1283, 1101, 1021, 970, 841, 775; MS m/z (% base): 382 (Mþ, 29), 381 (69),
311 (57), 227 (60), 214 (100), 197 (17), 170 (58), 145 (27) and 43 (100);
Anal calcd. for C22H30N4O2: C, 69.08; H, 7.90; N, 14.65. Found:
C, 69.10; H, 7.88; N, 14.69.
3-Dodecyl-10-hexylisoalloxazine (7): UV–visible (CHCl3), ꢁmax ("max
,
mM): 273 (42.05), 333 (10.14), 422 (7.67), 443 (10.72), 469 (6.90);
1H NMR (CDCl3): 8.17 (d, 1H, 6-H, J ¼ 8.13 Hz), 7.99–7.96 (m, 2H,
7-H, 9-H), 7.66 (t, 1H, 8-H, J ¼ 7.73 Hz), 4.60 (t, 2H, N10–CH2), 3.88
(t, 2H, N3–CH2), 1.74–1.24 (m, 28H, 14 Â CH2), 0.85 (t, 6H, 2 Â CH3);
IR (KBr): 2921, 2851, 2362, 1712, 1654, 1558, 1519, 1462, 1347, 1281,
1183, 767; MS m/z (% base): 466 (Mþ, 97), 423 (7), 396 (43), 339 (16),
299 (8), 227 (85), 214 (100), 170 (39), 143 (8) and 43 (100); Anal calcd.
for C28H42N4O2: C, 72.07; H, 9.07; N, 12.01. Found: C, 72.12; H, 9.06;
N, 12.03.
3-Allyl-10-hexylisoalloxazine (8): UV–visible (CHCl3), ꢁmax ("max
mM): 268 (94.25), 272 (94.25), 333 (20.84), 420 (21.73), 442 (26.82), 470
,
1
(18.10); H NMR (CDCl3): 8.32 (dd, 1H, 6-H, J ¼ 1.7 and 8.6 Hz), 7.90
(t, 1H, 7-H, J ¼ 8.4 Hz), 7.42 (t, 1H, 8-H, J ¼ 8.4 Hz), 7.18 (dd, 1H, 9-H,
J ¼ 1.2 and 8.4 Hz), 5.39–5.13 (m, 3H, CH¼CH2), 4.74–4.72 (m, 2H,
N10–CH2), 3.68 (d, 2H, N3–CH2), 1.34–1.25 (m, 8H, 4 Â CH2), 0.91 (t,
3H, CH3); IR (KBr): 2926, 2855, 1718, 1648, 1611, 1588, 1558, 1513,
1459, 1339, 1281, 1197, 920, 769; MS m/z (% base): 338 (Mþ, 15),
337 (70), 267 (78), 253 (92), 224 (17), 170 (64), 145, (81), 143 (29), 126 (68),
77 (18), 43 (78) and 41 (100); Anal calcd. for C19H22N4O2: C, 67.44;
H, 6.55; N, 16.56. Found: C, 67.41; H, 6.48; N, 16.59.
3-Benzyl-10-hexylisoalloxazine (9): UV–visible (CHCl3), ꢁmax ("max
,
mM): 273 (34.58), 334 (8.55), 423 (6.92), 443 (9.99), 472 (6.35); 1H NMR
(CDCl3): 8.30 (dd, 1H, 6-H, J ¼ 1.6 and 8.43 Hz), 7.86 (t, 1H, 7-H,
J ¼ 7.3 Hz), 7.63–7.58 (m, 3H, 8-H, 10-H, 50-H), 7.29–7.24 (m, 4H, 9-H,
20, 30, 40-H), 5.30 (s, 2H, N3–CH2), 4.66 (t, 2H, N10–CH2), 1.39–1.28 (m,

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Geetanjali,Singh,and Chauhan
8H, 4 Â CH2), 0.90 (t, 3H, CH3); IR (KBr): 2925, 2855, 2362, 1710, 1659,
1588, 1557, 1460, 1281, 1183, 763, 708; MS m/z (% base): 388 (Mþ, 14),
387 (52), 318 (26), 303 (42), 255 (25), 170 (31), 143 (17), 106 (54), 77 (16),
44 (100) and 43 (68); Anal calcd. for C23H24N4O2: C, 71.11; H, 6.23;
N, 14.42. Found: C, 71.15; H, 6.20, N, 14.46.
3-Butyl-10-hexadecylisoalloxazine (13): UV–visible (CHCl3), ꢁmax
("max, mM): 265 (17.79), 334 (5.73), 420 (3.13), 442 (3.87), 466 (2.65);
1H NMR (CDCl3): 8.60 (dd, 1H, 6-H, J ¼ 1.8 and 8.2 Hz), 7.90 (t, 1H,
7-H), 7.57 (t, 1H, 8-H), 6.93 (d, 1H, 9-H, J ¼ 8.1 Hz), 4.65 (t, 2H,
N10–CH2), 4.02 (t, 2H, N3–CH2), 1.60–1.23 (m, 32H, 16 Â CH2), 0.97
(t, 6H, 2 Â CH3); IR (KBr): 2926, 2854, 2362, 1712, 1682, 1610, 1589,
1554, 1514, 1458, 1280, 1192, 1115, 1070, 806, 767; MS m/z (% base): 494
(Mþ, 25), 493 (71), 464 (21), 438 (51), 311 (41), 227 (52), 215 (22), 214
(59), 170 (9), 143 (21) and 43 (100); Anal calcd. for C30H46N4O2: C, 72.84;
H, 9.37; N, 11.33. Found: C, 72.88; H, 9.34; N, 11.38.
3-Hexyl-10-hexadecylisoalloxazine (14): UV–visible (CHCl3), ꢁmax
("max, mM): 273 (29.90), 334 (7.19), 421 (5.79), 443 (7.66), 469 (4.50);
1H NMR (CDCl3): 8.49 (dd, 1H, 6-H, J ¼ 1.6 and 8.1 Hz), 7.88 (t, 1H,
7-H), 7.47 (t, 1H, 8-H), 6.98 (d, 1H, 9-H, J ¼ 8.2 Hz), 4.63 (t, 2H,
N10–CH2), 3.95 (t, 2H, N3–CH2), 1.66–1.24 (m, 36H, 18 Â CH2), 0.97
(t, 6H, 2 Â CH3); IR (KBr): 2921, 2850, 1712, 1655, 1613, 1590, 1558,
1520, 1492, 1463, 1374, 1283, 1185, 1116, 868, 766, 708; MS m/z (% base):
522 (Mþ, 24), 521 (78), 311 (49), 297 (29), 227 (41), 214 (79), 170 (48),
143 (17) and 43 (100); Anal calcd. for C32H50N4O2: C, 73.52, H, 9.64;
N, 10.72. Found: C, 73.57; H, 9.60; N, 10.73.
3-Dodecyl-10-hexadecylisoalloxazine (15): UV–visible (CHCl3), ꢁmax
("max, mM): 273 (33.63), 334 (8.79), 423 (7.98), 443 (8.88), 472 (7.18);
1
1H NMR (CDCl3): H NMR (CDCl3): 8.32 (dd, 1H, 6-H, J ¼ 1.7 and
8.2 Hz), 7.87 (t, 1H, 7-H), 7.37 (t, 1H, 8-H), 6.92 (d, 1H, 9-H,
J ¼ 8.1 Hz), 4.44 (t, 2H, N10–CH2), 3.88 (t, 2H, N3–CH2), 1.66–1.26 (m,
48H, 24 Â CH2), 0.98 (t, 6H, 2 Â CH3); IR (KBr): 2921, 2850, 1712, 1655,
1613, 1590, 1558, 1520, 1463, 1374, 1283, 1185, 920, 766; MS m/z (% base):
606 (Mþ, 21), 604 (41), 388 (74), 317 (33), 303 (37), 274 (19), 214 (68), 170
(37), 143 (16), 91 (43), 44 (100) and 43 (92); Anal calcd. for C38H62N4O2:
C, 75.20; H, 10.30; N, 9.23. Found: C, 75.24; H, 10.31; N, 9.28.
3,10-Dihexadecylisoalloxazine (16): UV–visible (CHCl3), ꢁmax ("max
,
1
mM): 272 (25.53), 334 (6.27), 424 (5.58), 444 (7.44), 468 (5.26); H NMR
(CDCl3): 8.35 (dd, 1H, 6-H, J ¼ 1.6 and 8.2 Hz), 7.83 (t, 1H, 7-H), 7.34
(t, 1H, 8-H), 6.82 (d, 1H, 9-H, J ¼ 8.1 Hz), 4.43 (t, 2H, N10–CH2), 3.98
(t, 2H, N3–CH2), 1.68–1.25 (m, 56H, 28 Â CH2), 0.98 (t, 6H, 2 Â CH3);
IR (KBr): 2926, 2854, 2362, 1712, 1682, 1610, 1589, 1554, 1514, 1458,
1280, 1192, 1115, 1070, 806, 767; MS m/z (% base): 662 (Mþ, 21),

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N-3 Alkylation of 10-Substituted Isoalloxazines
619
494 (86), 439 (9), 270 (10), 227 (75), 215 (37), 214 (54), 170 (11), 144 (7),
143 (57) and 43 (100); Anal calcd. for C42H70N4O2: C, 76.08; H, 10.64;
N, 8.45. Found: C, 76.04; H, 10.69; N, 8.42.
3-Ethyl-10-phenylisoalloxazine (19): UV–visible (CHCl3), ꢁmax ("max
,
mM): 273 (27.29), 337 (7.46), 425 (6.20), 445 (7.98), 469 (5.22); 1H NMR
(CDCl3): 8.22 (d, 1H, 6-H, J ¼ 7.8 Hz), 7.77–7.42 (m, 7H, 7-H, 8-H and
Ar–H), 6.81 (d, 1H, 9-H, J ¼ 8.39 Hz), 3.94 (q, 2H, N3–CH2), 1.17 (t, 3H,
CH3); IR (KBr): 2927, 2368, 1703, 1650, 1556, 1460, 1350, 1267, 1202,
766, 700; MS m/z (% base): 318 (Mþ, 21), 303 (10), 289 (41), 241 (56), 227
(8), 170 (56), 77 (100) and 43 (48); Anal calcd. for C18H14N4O2: C, 67.92;
H, 4.43; N, 17.60. Found: C, 67.92; H, 4.40; N, 17.67.
ACKNOWLEDGMENTS
Research scholars G and RS are thankful to CSIR and UGC,
respectively for fellowships. SMSC is thankful to DBT and CSIR for
financial support.
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Received in the UK December 3, 2001