Synthesis and characterization of nucleoside derivatives, N-(benzoyl)-N-(deoxyguanosin-8-yl)-4-aminobiphenyl and N-(2′-deoxyguanosin-8-yl)-4-aminobiphenyl via α-phenyl-N-(4-biphenyl)nitrone

Article abstract of DOI:10.1081/NCN-120006832

Lead tetraacetate (LTA) oxidation of α-Phenyl-N-(4-biphenyl)nitrone (8) to give a new ultimate carcinogen, N-acetoxy-N-benzoyl-4-aminobiphenyl (9) which was reacted with deoxyguanosine (dG) at pH 6.9 to give nucleoside derivative, N-(benzoyl)-N-(deoxyguan

Full text of DOI:10.1081/NCN-120006832

Nucleosides, Nucleotides and Nucleic Acids
ISSN: 1525-7770 (Print) 1532-2335 (Online) Journal homepage: http://www.tandfonline.com/loi/lncn20
SYNTHESIS AND CHARACTERIZATION OF
NUCLEOSIDE DERIVATIVES, N-(BENZOYL)-N-
(DEOXYGUANOSIN-8-YL)-4-AMINOBIPHENYL AND
N-(2′-DEOXYGUANOSIN-8-YL)-4-AMINOBIPHENYL
VIA α-PHENYL-N-(4-BIPHENYL)NITRONE
H. Mallesha , K. R. Ravi Kumar & K. S. Rangappa
To cite this article: H. Mallesha , K. R. Ravi Kumar & K. S. Rangappa (2002) SYNTHESIS AND
CHARACTERIZATION OF NUCLEOSIDE DERIVATIVES, N-(BENZOYL)-N-(DEOXYGUANOSIN-8-
YL)-4-AMINOBIPHENYL AND N-(2′-DEOXYGUANOSIN-8-YL)-4-AMINOBIPHENYL VIA α-PHENYL-
N-(4-BIPHENYL)NITRONE, Nucleosides, Nucleotides and Nucleic Acids, 21:4-5, 385-392, DOI:
10.1081/NCN-120006832
To link to this article: http://dx.doi.org/10.1081/NCN-120006832
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©2002 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.
NUCLEOSIDES, NUCLEOTIDES & NUCLEIC ACIDS, 21!4&5), 385±392 !2002)
SYNTHESIS AND CHARACTERIZATION OF
NUCLEOSIDE DERIVATIVES, N-ꢀBENZOYL)-N-
ꢀDEOXYGUANOSIN-8-YL)-4-AMINOBIPHENYL
AND N-ꢀ20-DEOXYGUANOSIN-8-YL)-4-
AMINOBIPHENYL VIA a-PHENYL-N-ꢀ4-
BIPHENYL)NITRONE
H. Mallesha, K. R. Ravi Kumar, and K. S. Rangappa*
Department of Studies in Chemistry, University of Mysore,
Manasagangotri, Mysore-570 006, India
ABSTRACT
Lead tetraacetate !LTA) oxidation of a-Phenyl-N-!4-biphenyl)nitrone !8)
to give a new ultimate carcinogen, N-acetoxy-N-benzoyl-4-aminobiphe-
nyl !9) which was reacted with deoxyguanosine !dG) at pH 6.9 to give
nucleoside derivative, N-!benzoyl)-N-!deoxyguanosin-8-yl)-4-aminobi-
phenyl !10). Following debenzoylation with sodium carbonate-methanol
leads to N-!20-deoxyguanosin-8-yl)-4-aminobiphenyl !11).
Key Words: Nucleoside derivatives; LTA oxidation; a-Phenyl-N-!4-bi-
phenyl)nitrone; N-!benzoyl)-N-!deoxyguanosin-8-yl)-4-aminobiphenyl
4-Aminobiphenyl ꢀ1), 4-acetylaminobiphenyl ꢀ2), N-hydroxy-4-aminobiphe-
nyl ꢀ3) and N-hydroxy-4-acetylaminobiphenyl ꢀ4) form a class of compounds
induce tumours in a wide variety of tissues in a number of species.[1±6] The
carcinogenicity of 1, 2, 3 and 4 depend on their activation to become reactive
metabolites 5 or 6 or N-hydroxy derivatives.[7±16] Di€erent pathways have
*Corresponding author. Fax: 91821-518835 and 91821-421263; E-mail: rangappaks@
yahoo.com
385
Copyright # 2002 by Marcel Dekker, Inc.
www.dekker.com

386
MALLESHA, RAVI KUMAR, AND RANGAPPA
Scheme 1.
been developed in both in vivo and in vitro for the activation of 1, 2, 3 and 4
into their reactive metabolites 5 and 6,[10±16] as shown in Sch. 1. The meta-
bolites 5 and 6 are putative reactive species, react with !bio)nucleo-
philes.[11,17±21] to form adducts and are directly responsible for the induction
of cancer.[17±21]
Recently, we have synthesized a new class of carcinogens, N-acetoxy-
N-benzoylarylamines from arylnitrones[22,23] of phenyl moiety to form C8
adduct with dG and they are also shown to be reactive metabolites like N-
acetoxyanilines.[14] Now, we have extended this study with polynuclear nitrone
8 to check its reactivity and justi®cation for the earlier reactions made. Hence,
we report the synthesis of a new ultimate carcinogen N-acetoxy-N-benzoyl-4-
aminobiphenyl 9 by LTA oxidation[24±26] of a-Phenyl-N-!4-biphe-nyl)nitrone
8 and the reaction of 9 with the dG, ®nally the debenzoylation of N-!benzoyl)-

SYNTHESIS AND CHARACTERIZATION OF NUCLEOSIDE DERIVATIVES
387
Scheme 2. Reagents and conditions: i, Zn=NH4Cl, Cat histidine, distilled H2O-DMF, 20±
30ꢀC, 90 min, pH 7.4±7.5; ii, PhCHO=EtOH, 5±10ꢀC, 3 h, overnight 0ꢀC; iii, LTA=anhyd
benzene, 0ꢀC, 20 min; iv, 95% EtOH, dG=2 mM sodium citrate bu€er of pH 6.9, 55ꢀC, 3 h,
then 60ꢀC, 2 h; v, anhyd Na2CO3=MeOH, r.t. 6±7 h.
N-!deoxyguanosin-8-yl)-4-aminobiphenyl 10 with heterogeneous system into
C8 adduct, N-!20-Deoxyguanosin-8-yl)-4-aminobiphenyl 11 !Sch. 2).
RESULTS AND DISCUSSION
Compound 3, precursor for the synthesis of 8 was prepared by the
reduction of 4-nitrobiphenyl ꢀ7) using modi®ed procedure of patric[27]
method with zinc-ammonium chloride and catalytic amount of histidine[28] in
a solvent mixture of water-N, N-dimethyformamide !1:1). Condensation of 3
with freshly distilled benzaldehyde in ethanol gave nitrone 8. IR absorption
at 1540 cmÀ 1 and 1H NMR singlet peak at d 8.04 con®rmed the presence of
CHˆN group in 8. Compound 8 was found to be acid sensitive[29] and light
sensitive,[30] decomposes to aldehyde, amine, nitroso, imine, azo compound

388
MALLESHA, RAVI KUMAR, AND RANGAPPA
etc. Hence, it was stored in the freeze under dark until further use. 1H NMR,
IR and elemental analysis studies are con®rmed the structure of 8.
A new N-benzoylated ultimate carcinogen 9 was prepared by LTA
oxidative rearrangment reaction[31] in benzene. The reaction was found to be
exothermic, temperature dependent and maintained at 0ꢀC. The reaction
appears to proceed through the intramolecular acetyl transfer,[22] leads to the
formation of 9. Compound 9 was obtained as crystalline white solid after
1
puri®cation and found to be stable for a week at À 10ꢀC. H NMR and IR
studies are made to con®rm the product 9. IR absorption peaks at d 1678 and
1790 cmÀ 1 are assigned to amide, CˆO and ester CˆO stretching frequency
respectively, con®rmed the presence of OCOCH3 and COPh groups. In
the 1H NMR spectrum, a singlet peak at d 2.26 is assigned to OCOCH3. Other
spectral data are consistent with the structure 9. Satisfactory results are
obtained by elemental analysis. All attempts to synthesize 9 by O-acetyl-ation
to 8 with acetyl chloride, acetic anhydride and benzoyl choloride are failed.
Reaction of 9 with deoxyguanosine !dG) in sodium citrate bu€er of pH
6.9 at 55ꢀC gave a new N-benzoylated nucleoside derivative 10. The yield of
the product 10 is 26%, which is much improved yield compared to its ana-
1
logous.[10,12,14] The H NMR, IR and elemental analysis data con®rmed the
structure of 10. The absence of C8-H proton of dG[32] in the region d 8.01
indicates that substitution had taken place at C8 position of dG ring. The
NH2 and NH protons of dG moiety appeared at d 6.37 and 10.57 respec-
tively. All the active hydrogens of NH and OH disappeared upon addition of
D2O indicate that NH and OH sites are free from substituent. Other spectral
data are also consistent with the structure 10.
The compound 10 was debenzoylated[10] to form an authenticated
product[12] 11. Appearance of NH proton at d 8.68 and disappearance of this
active NH proton upon addition of D2O con®rmed the product 11.
The spectral data assigned for 10 ruled out the other possible N2 adduct
12, since C8-H proton was absent, it would have eight aromatic protons
instead of nine, and 13, since both NH-NH protons were absent. Thus, the
presence of nine aromatic protons at d 7.06±7.79 indicated that none of the
aromaticprotons in the biphenyl moiety are substituted. Moreover, these
signals strongly support the point of link at C8 of dG through the biphenyl
nitrogen.

SYNTHESIS AND CHARACTERIZATION OF NUCLEOSIDE DERIVATIVES
389
LTA oxidation of 8 to give 9, inturn reacted with dG to form C8 adduct
10. This concludes: !i) 9 is also a new reactive metabolite like other N-
acetoxyarylamines and amides reported earlier,[10±15,22,23] !ii) nitrone 8 is also
a precarcinogen i.e., it is essentially require activation to produce the reactive
metabolite 9. Therefore, LTA is used as an excellent oxidant[24,25] to activate
8 into reactive metabolite 9. This is a simple activation pathway to 9, a new
reactive metabolite via nitrone 8.
EXPERIMENTAL TLC was performed with 0.2 mm silica gel GF254
!E-merck) with ¯uorescent indication. Melting points were recorded on
1
SELACO 605 melting point apparatus and were uncorrected. H NMR
Spectra were recorded on Bruker AMX-400, 400 Mz, NMR spectro-
photometer using CDCl3 and DMSO-d6 as solvent with TMS as internal
standard. IR spectra are recorded on a Bio-Rad Win-IR spectrometer. Low
temperature reactions are carried out using cryostat model MRP 700. All
HPLC analysis are performed with Lachrom-2000 Merck-Hitachi L7100
pump with RP18.250-4 mm column and UV Detector-UV-VIS L7400.
a-Phenyl-N-ꢀ4-biphenyl)nitrone ꢀ8). Equimolar solutions of N-4-!bi-
phenyl)hydroxylamine 3 and benzaldehyde in minimum volume of ethanol-
ether !1:1) was kept at 5±10ꢀC and set aside in the dark for 3 h. Ether was
removed under reduced pressure. Resulting mixture was freezed overnight in
dark. Separated needles were recrystallized from ethanol to give 8 as white
crystalline solid. Yield !98%); mp 105±107ꢀC; 1H NMR !CDCl3): d 7.52±7.98
!m, 10 H, Ar-H), 8.04 !s, 1H, CHˆN), 8.25±8.62 !m, 4 H, Ar-H); IR !Par-
an):1540 !CˆN), 1090 cmÀ 1 !NO). Anal. Calcd. for C19H15NO: C, 83.51;
H, 5.49; N, 5.31. Found: C, 83.48; H, 5.48; N, 5.16.
N-Acetoxy-N-benzoyl-4-aminobiphenyl ꢀ9). LTA !800 mg, 1.80 mmol)
was added to nitrone 8 !500 mg, 1.83 mmol) in 10 ml benzene at 0ꢀC and the
mixture was stirred in cold condition for 10 min. After 10 min, white lead
diacetate was ®ltered at room temperature and evaporation of the solvent at
reduced pressure a€orded 9 as solid. It was repeatedly washed with cold
! À 20ꢀC) ether. Finally it was recrystallised from ether-petroleum mixture to
give crystals of 9. Yield was 508 mg !85%); mp 97±99ꢀC; 1H NMR !CDCl3):

390
MALLESHA, RAVI KUMAR, AND RANGAPPA
d 2.26 !s, 3H, OCOCH3), 7.34±7.40 !d, 2H, Ar-H), 7.72±7.86 !m, 10 H, Ar-
H), 7.90±8.01 !d, 2 H, Ar-H); IR !KBr): 1678 !CˆO str, PhCON), 1790
!CˆO str, OCOCH3), 1480, 1486 !CÀN str), 1217 cmÀ 1 !C-O str,
OCOCH3). Anal. Calcd. for C21H17NO3: C, 76.13; H, 5.13; N, 4.23. Found:
C, 76.15; H, 5.13; N, 4.26.
N-ꢀ20-Deoxyguanosin-8-yl)-4-benzoylaminobiphenyl ꢀ10). Compound 9
!281 mg, 0.85 mmol) in 15 ml of 95% ethanol was added to dG !49 mg,
0.17 mmol) in 30 ml of 2 mM sodium citrate bu€er[33] of pH 6.9 at 55ꢀC over
2 h and the mixture was stirred further for 3 h at 60ꢀC. The reaction mixture
was diluted with 60 ml of water and ®ltered. The ethanol was evaporated and
the aqueous phase was extracted with ether !3610 ml) and ethyl acetate
!3615 ml). The combined extracts were dried over anhydrous sodium sulfate
and evaporated to give crude solid product 10. Compound 10 was washed
over a silica gel column with ether-benzene !1:1) and eluted with methanol-
chloroform !7:4). Second fraction was re-chromatographed over a sephadex
G-15 with ethanol-chloroform !7:4) to give pure solid product 10 !24 mg,
26%), which was stable in neutral aqueous solution for several weeks at 0ꢀC.
Analysis of the aqueous solution with HPLC using water-acetonitrile !6:1)
1
showed that the product was 98.8% pure. H NMR !DMSO-d6): d 2.06 !m,
2H2 ), 3.75 !m, 2H5 ), 4.04 !m, 1H4 ), 4.46 !m, 1H3 ), 5.36 !s, 1H3 , OH), 6.02
1
1
1
1
1
1
1
!s, 1H5 , OH), 6.20 !m, 1H1 ), 6.37 !s, 2H, Gu-NH2), 7.06±7.38 !m, 5H,
COÀAr-H), d 7.41 !d, 2H, BP), 7.52!t, 1H, BP), 7.63 !t, 2H, BP), 7.79 !dd,
4H, BP), 10.57 !s, 1H, Gu-NH); IR !KBr): 3330, 2928, 1680, 1644, 1562,
1355, 1052, 1025, 1013,960 cmÀ 1. Anal. Calcd. for C29H26N6O5: C, 64.68; H,
4.83; N, 15.61. Found: C, 64.66; H, 4.87; N, 15.65.
N-ꢀ20-Deoxyguanosin-8-yl)-4-aminobiphenyl ꢀ11). This was prepared
by using Underwood procedure.[10] Compound 10 was debenzoylated with
heterogeneous system, sodium carbonate-methanol to give 11. Spectral data
[12,34]
of 11 is in good agreement with the data of authenticsample.
ACKNOWLEDGMENT
We are grateful to the Department of Science and Technology !DST),
Government of India, New Delhi, for ®nancial support under the project vide
No. SP=S1=GO5=97.
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