Synthesis and Characterization of Nitrogen-Bridged [C₆₀]Fullerene/3′-Deoxythimidine Conjugates

Abstract

3¢-Deoxy-3¢-(1,2,3-triazolfulleryl)thymidine and 3¢-deoxy-3¢- ([5,6]azafulleryl)thymidine were synthesized by the addition of 3¢-azido-3¢-deoxythymidine (AZT) to C 60 .The synthesis and biological proprieties of water-soluble C 60 derivatives have been an area of intensive investigation over the past decade. Functionalization by [3+2] cycloaddition reactions represents the most used strategy to prepare stable cycloadducts with biological activity. [1][2][3][4][5] Starting with the work of Bingel 6 in the [2+3] cycloaddition of a stabilized a-halocarbanion to the C 60 core, attachment of substrates to give water-soluble methanofullerenes has enabled chemists to prepare products with promising preliminary biological activities, such HIVprotease inhibition, 7-10 neuroprotection and apoptosis, 1-13 and DNA photocleavage. 14 Fulleropyrrolines with different biological active substituents on nitrogen have been prepared by cycloaddition of azomethine ylides to fullerene. 15,16 Other versatile but much less investigated for biological applications are the nitrogen-bridged adducts of fullerene. Prato et al. 17 first reported the [2+3] cycloaddition of organic azides to C 60 to yield azafulleroids. Although this chemistry has been developed to prepare a series of nitrogen-bridged C 60 cycloadducts, only a few of them are designed as biological materials. 18-21 Despite this array of encouraging work, however, no water-soluble fullerene-nucleoside analogues has heretofore been reported. Thus, it was of interest to synthesize nitrogenbridged C 60 -3¢-deoxythimidine adducts, which should open a new frontier to nucleoside analogue chemistry for biological applications. In this paper, we report our preliminary results on the reaction of C 60 with 3¢-azido-3¢-deoxythymidine (AZT), the well-known anti-HIV agent.Treatment of a solution of C 60 with AZT in 1,2-dichlorobenzene (ODCB) at 30°C gave the 3¢-deoxy-3¢-(1,2,3-triazolfulleryl)thymidine (1) in 44% yield after purification by column chromatography. Photolysis of 1 in toluene (0.84 × 10 -4 M, l max = 300 nm) yielded the aziridinofullerene derivative 3. Thermally induced conversion of 1 predominantly afforded opened 5,6-addition type azafulleroid 2 beside C 60 . When a mixture of C 60 and AZT was heated in ODCB at 120°C, 2 was obtained as the major product (50%) (Scheme 1). Compounds 1-3 are readily soluble in DMSO, THF, toluene and ODCB. They are also soluble in water [3 mg/mL (1), 2.5 mg/mL (2)]. The solubility in water was checked by adding a solution of products 1-3 in DMSO or THF to water (1:10). The structures of the products 1-3 were determined by elemental and spectroscopic analyses. Scheme 1The TOF MS spectra show the parent ion peaks at m/z = 987.860 (1), 959.847 (2), and 959.848 (3), which agree with the theoretically predicted patterns of isotopic distribution. The 1 H NMR spectra confirmed the thymidine backbone structures of the compounds 1 and 2 for the Downloaded by: University of Queensland. Copyrighted material.

Mass spectrometric characterization of 3′‐imino[60]fulleryl‐3′‐deoxythymidine by collision‐induced dissociation

“…The 1 H NMR spectral data (not shown) obtained in 100% deuterated toluene (Aldrich) revealed peaks corresponding to the deoxyribose and thymidine units. As observed by Prato et al for other adducts, and by Ungurenasu et al ,7 the 1 H NMR spectrum of the nucleoside unit is very similar to that of the starting nucleoside analog with a small downfield shift due to the influence of the fullerene. No apparent hydrogen transfer from the nucleoside to the [60]fullerene is detected.…”

“…This paper discusses the interaction between C 60 and the added 3′‐azido‐3′‐deoxythymidine (AZT) using mass spectrometry. The synthesis of this compound was first reported by Ungurenasu et al 7 Our interest is motivated by the use of C 60 as a transducer/reporter unit. First, the free 5′‐end of the nucleoside can undergo the addition of nucleotides using phosphoramidite chemistry,8 which makes it possible to synthesize a DNA strand capped at the 3′‐end by an imino[60]fullerene without making use of linkers.…”

Charge Distribution in 3′‐Deoxythymidine‐Fullerene: Mass Spectrometry, Laser Excitation, and Computational Studies

“…C 60 1–4 is an ideal and promising building block for molecular devices and numerous biological applications 5–11 due to its unique properties, viz., an almost nano‐dimensional size, three‐dimensional cage topology, hydrophobicity, rich redox‐ and photochemistry, large absorption cross section, and other electronic effects. It can be functionalized, 12–15 anchored to a surface, and self‐assembled into larger supramolecular entities such as monolayers 12–14 .…”

“…We have recently reported 15 the functionalization of C 60 by a thymidine analogue, leading to the formation of 3′‐imino[60]fulleryl‐3′‐deoxythymidine (FdT) 10 (Fig. 1).…”

“…For example, C 60 -based donor-acceptor or donor-bridge-acceptor complexes have been investigated for their possible application as photovoltaic devices. [16][17][18][19][20][21] We have recently reported 15 the functionalization of C 60 by a thymidine analogue, leading to the formation of 3′-imino[60]fulleryl-3′-deoxythymidine (FdT) 10 (Fig. 1).…”