1. Introduction
With the high abilities in recognizing specific DNA sequence and catalyzing hydrolysis of phosphate diester bonds, chemical nucleases have rapidly become an invaluable research tool in the fields of biology, bioorganic chemistry, therapy, and molecular biology [1] - [6] . Many complexes have been designed and studied. In this used ligands, cyclen with four benzyl groups, can coordinate with most mental cations or negative ion. The successful application of several cyclen derivative complexes for biomedical applications has stimulated interest for new cyclen-based ligands with different types of pendant arms in an attempt to find new ligands with different chemical, biological or catalytic properties [7] [8] [9] [10] [11] . Since armed cyclens have many structural and geometrical variations, they form a wide variety of metal complexes having specific sensing and signaling functions [12] .
Recently, many cyclen derivatives with different types of pendant arms have been designed and reported, but only a few compounds bearing four benzyl groups. Smith C. B. and coworkers reported the preparation of the cyclen derivatives: (R)-thppc12 (L) and (S)-thph-pc12 (L’), including four benzyl or phenoxy-methyl groups, where benzyl or phenoxymethyl groups project in the same direction due to the open nature of the electron-rich cavity [13] . If, in addition to bearing a donor atom, the pendant arms also have an aromatic moiety attached to them, the possibility arises of using the coordination of the ligand to a metal ion as a way of assembling a molecular receptor with a substantial cavity.
Encouraged by these considerations, we describe herein the synthesis of a new type of cyclen-base ligand with four neutral pendent groups at N residuals according to Scheme 1. Herein, X-ray crystal structure determination of compound 1 is undertaken to better understand the influence of structure modifications upon overall molecular geometry and conformation.
2. Experimental Section
2.1. Materials and Instruments
All chemicals were of reagent grade and used without further purification. All aqueous solutions were prepared from deionized or distilled water. Reaction and the resultant products were monitored by thin-layer chromatography (TLC) on Merck pre-coated silica gel F254 plates with separated compounds visualized at 254 nm under a UV lamp. Melting point (uncorrected) was determined on a XT4 MP: apparatus (Taike Corp, Beijing, China). NMR was recorded in CDCl3 on a Varian Mercury 300 spectrometer and resonance was given in ppm (δ) relative to TMS.
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Scheme 1. Synthetic route to compound 1.
2.2. Synthesis of the Title Compound (1)
Compound 1 was synthesized based on literature method (Scheme 1) [14] . To a solution of cyclen (0.2 g, 1.16 mmol), 1-(2-bromoethoxy)-4-methoxybenzene (1.34 g, 5.8 mmol) in 30 mL CH3CN was added K2CO3 (0.83 g, 6.0 mmol). The resulting solution was heated under reflux and the progress of the reaction was monitored by TLC (CH2Cl2/CH3OH 7:1 silica gel). After disappearance of the starting material (ca. 8 h), the remaining solids were removed by filtration, and the filtrate was cooled to give compound 1, white solid, yield: 89.5%. Melting point: 128˚C - 129˚C. 1H NMR (300 MHz, CDCl3), δ (ppm): 6.79 - 6.69 (16H, dd, C6H4), 4.02 (8H, s, cyclen-CH2CH2O), 3.75 (12H, s, OCH3), 3.27 (8H, s, cyclen-CH2CH2O), 3.13 (16H, s, NCH2CH2N).