-90°C). When the temperature was near -60°C. quenching of the solution in water and standard workup afforded crude reaction products in ca. 90Yo yield (GC). Purification (recrystallization or column chromatography) gave pure products.[9] Only the Markownikoff regioisomer 9 (by GC and I3C NMR analyses) was fund to be present in yields of 69%-91% after quenching in water.Academic Press, Orlando, FL, USA 1984, Chapter 5, p. 341. Chem. 88 (1976 Cyclobis(paraquat-p-phenylene). A Tetracationic Multipurpose ReceptorBy Barbara Odell, Mark V. Reddington, Alexandra M. Z . Slawin, Neil Spencer, J. Fraser Stoddart,* and David J . WilliamsRecently, we reported''] on cyclophane-like molecular receptors, such as bisparaphenylene-34-crown-10 1, which contains n-electron-rich hydroquinone units for face-to-face complexation ( Fig. 1) with paraquat 2, a n-electron-deficient dication. These observations led us to propose that it might be possible to reverse constitutionally the roles of the receptor and the substrate and so bind a n-electronrich diphenol ether, such as 1,4-dimethoxybenzene 3a, inside a tetracationic molecular receptor (Fig. 1). Such a receptor is the tetracation cyclobis(paraquat-p-phenylene) 4 which incorporates two n-electron-deficient paraquat residues connected in a phane-like manner by means of two para-phenylene groups.[21 Here, we describe (i) the synthesis of 4 as its tetrakis(hexafluorophosphate) 4 . 4 PF,, (ii) its X-ray structural characterization as the acetonitrile solvate 4 . 4 PF6.3 MeCN, (iii) the UV and 'H-NMR spectroscopic evidence for 1 : 1 complex formation (a) between 4 . 4 PF6 and 1,2-, 1,3-, and 1,4-dimethoxybenzene 3a/3b/ 3c in acetonitrile (CD,CN) and (b) between 4 . 4 C I and 1,4-dihydroxybenzene 6 in water (D20)J3' and (iv) the results of molecular and semiempirical quantum mechanical calculations on 4 and on 4 . 2 MeCN.[ Fig. 1 Schematic representation of the basis for the proposal that the cyclobis(paraquat-p-phenylene) 4 should act as a tetracationic receptor for 1,4-dimethoxybenzene 3a.The procedure (cf. Ref.[2]) employed for the preparation of 4 -4 P F 6 starting from the bis(pyridinium) salt 5 and 1,4-bis(bromomethyl)benzene is outlined in Scheme 1. (Fig. 2, top) that 4 adopts a rigid centrosymmetric rectangular box-like conformation with the two paraquat units forming the longer sides and the two para-xylylene residues, the shorter ones. There is a 19" twist angle between the two pyridinium rings of each paraquat unit: in addition, there are deformations of both the paraquat and para-xylylene components producing a bowing of the sides of the cyclophane. Thus, the strain within the molecule is relieved by out-of-plane bending of the six aromatic rings and is distributed throughout the macrocycle with the maximum deviations associated with the exocyclic C-CH2 bonds emanating from the para-phenylene residues: these bonds subtend an angle of 14" with respect to each other whilst the two Ne-CH, bonds associated with the paraquat units subtend an angle of 23 O . There is also a con...

tided as ca. 99% unreacted 'H NMR (vide supra). The components of the aqueous phase were identified by 'H NMR as paraquat (S 4.35 (s, 3 H), 8.37 (d, J = 1,2 H), 8.90 (d, J = 1,2 H)) and 2-(ethylamino)-2-methylpropanol hydrochloride (spectrum identical to that described above). Integrals of the NMR signals for paraquat and the amino alcohol indicated a 2.5% conversion of DEM-3 dimer to the amino alcohol.B. Buffered Methanol Medium. The reaction was performed in pH 7, Tris-buffered methanol. This time the reaction mixture turned dark blue. Again, the residue from solvent evaporation was extracted into 1 mL of D20 and 1 mL of CDC13. The components of the organic phase were identified by 'H NMR as DEM-3 dimer and 2-(ethylamino)-2methylpropanol (6 1.06 (s, 6 H), 1.07 (t, J = 7.2, 3 H), 2.44 (q, J = 1.2, 2 H), 3.33 (s, 2 H)). The components of the aqueous phase were identified as paraquat and a small amount of 2-(ethylamino)-2-methylpropanol hydrochloride, also from the 'H NMR spectrum. Integrals of the NMR signals indicated a 41% conversion of DEM-3 dimer to amino alcohol.Attempted Reduction of Daunomycin with DEM-3 Dimer. The reaction vessel was a 9 mm X 20 cm Pyrex tube equipped with a 2.5-cm side arm. The side arm was charged with 2.65 X 10"* mol of DEM-3 dimer dissolved in methylene chloride, and the methylene chloride was evaporated with a stream of nitrogen. The main tube was charged with 2 mL of 2 X 10~3 M 1:1 Tris/Tris-HCl buffered methanol containing 2.66 X 10"6 mol of daunomycin. The methanol solution was freeze-thaw-degassed, and the tube was sealed with a torch. After mixing the reagents, the solution was heated at 36 °C for 18 h. C-18 reverse-phase HPLC analysis as described earlier35 showed no formation of 7-deoxydaunomycinone.

Metal-organic frameworks (MOFs) represent [1] an extensive class of porous crystals in which organic struts link metalcontaining clusters. The success in controlling the functionality and structure of MOFs has led to numerous applications, [2] most notably gas adsorption, [3] storage of clean gas fuels, [4] catalysis, [5] separations, [6] and drug delivery. [7] However, the vast majority of MOFs described to date are composed of organic struts derived from non-renewable petrochemical feedstocks and transition metals. The challenge in preparing MOFs from natural products lies in the inherent asymmetry of the building units, which are not amenable to crystallization in the form of highly porous frameworks. Herein, we report a strategy to overcome this problem using g-cyclodextrin (g-CD), a symmetrical cyclic oligosaccharide that is mass-produced enzymatically from starch [8] and comprised of eight asymmetric a-1,4-linked dglucopyranosyl residues. These g-CD building units are then linked by potassium ions, in aqueous media at ambient temperature and pressure, to form a body-centered cubic structure, termed CD-MOF-1, which has the empirical formula [(C 48 H 80 O 40 )(KOH) 2 ] n . CD-MOFs can be prepared entirely from edible ingredients: combining food-grade g-CD with salt substitute (KCl) or potassium benzoate (food additive E212) in bottled water and Everclear grain spirit (EtOH) yields porous frameworks which constitute edible MOFs.While there have been a few reports of MOFs assembled from amino acids, [9] nucleobases, [7a, 10] peptides, [11] magnesium formates, [12] and metal glutarates, [13] examples of these materials are not common despite the rapidly growing desire to fabricate MOFs from naturally available building blocks. We suspect that the key to our success in assembling CD-MOFs lies in the symmetric arrangement (C 8 ) within the g-CD torus of eight asymmetric (C 1 ) a-1,4-linked d-glucopyranosyl residues and the ready availability of g-CD as a chiral molecular building block (Figure 1). CD-MOF-1 was prepared by combining 1.0 equiv of g-CD with 8.0 equiv of KOH in aqueous solution, followed by vapor diffusion of MeOH into the solution during 2-7 days, resulting in colorless, cubic, single crystals, suitable for X-ray crystallography, in approximately 70 % yield. Other CD-MOFs were readily obtained using salts of Na + , Rb + , and Cs + , giving rise to an extensive new family of porous materials. A complete list of metal salts employed to form CD-MOFs and the full synthesis of CDMOFs are provided in Section S2 of the Supporting Information.The X-ray crystal structure of CD-MOF-1 [14] reveals that eight-coordinate K + ions not only assist in the assembly of (g-CD) 6 cubes (Figure 2 a,b), wherein six g-CD units occupy the faces of a cube, but they also serve to link these cubes together in a three-dimensional array which extends throughout the crystal (Figure 2 c). The (g-CD) 6 repeating motifs adopt a body-centered cubic packing arrangement wherein each symmetrically equivalent K + ion links two co...

A template‐controlled, one‐pot reaction afforded the [2]catenane 1 in 70% yield. Compound 1 consists of π‐electron‐rich decaoxa[13.13]paracyclophane (empty circles) and an electron‐deficient macrocycle made up of two paraquat p‐phenylene units (filled circles). Dynamic 1 H NMR spectroscopy and cyclovoltammetry showed that 1 is highly ordered not only in the solid state but also in solution.

COMMUNICATIONS z and p anomers (10190) of 2,3,4,6-aceto-1(2-bromoethoxy)-~-galactose in 68% yield (8.3 8). The purified fi anomer could be obtained by flash chromatography. Stereochemical assignments were made by an X-ray crystal structure of the fi anomer. 2,3,4,6-tetraacetyl-l-(2-bromoethoxy)-~-galactose was treated with cyclene to produce the monosubstituted product. The acetate protecting groups were cleaved, and the three carboxyhc acid substituents were added by reaction with bromoacetic acid at pH 10.5. The product 4,7,10-tri(acetic acid)-l-(2-~-galactopyranosylethoxy)-I ,4,7,1O-tetraazacyclododecane was isolated by anion exchange fast performance liquid chromatography (FPLC, detection at 218 nm) in 37% overall yield. Gd3+ or Tb" ions were incorporated into complexes, and these (EGad-Gd and EGad-Tb) were purified by repeated collections on a reverse phase HPLC analytic C,, column with waterlacetonitrile (0-10% gradient) as the eluent (fluorescence detection = 274 nm and i,, = 315 nm) in 70% yield. The high resolution mass spectrum of the isolated solid provided a parent molecular ion (M+Na)+, which exhibited the correct exact mass and the predicted isotope ratios. X-ray data for C,,H,,O,,Br: CAD-4 diffractometer; monoclinic, colorless plates, space group F"2, (no. 4); a total of 5603 reflections measured, 2981 used for refinemen t . Fluorescence experiments [5,6] with EGad: The decay rate (inversely proportional to the lifetime) of the emission peak at 1 . -= 545 nm (& = 460 nm) was measured with a Hitachi f-4500 fluorescence spectrophotometer (2 s delay, 64 scans) in H,O, 50150 H,O/D,O, and D,O. An exponential curve fit (DeltaGraph 3, Delta Point Inc., Monterey, CA) was used to determine the decay rates. The slope of the decay rates versus D,O concentration was compared to the literature value of a slope of 0.2391q to obtain q.In three identical inversion-recovery (IR-NMR) high resolution experiments (Bruker AMX 500, 26°C) EGad(2 mM) was incubated with two different concentrations ofp-gal (1.7 p~ and 5.1 PM) heat-inactivated p-gal(l0 min at 80', 5.1 pM), and EGad alone (2 mM) in phosphate buffer (25 mM, pH 7.3) at 37 "C. Minimal enzyme concentrations were used to reduce potential interactions between the contrast agent and the enzyme. The solutions in a 40 pL round-bottomed NMR tube insert (Wilmad glass) were placed into a 5 mm NMR tube containing CD,CI. Tl measurements were made immediately following mixing and after complete cleavage of the galactopyranose (> 95 % after incubation for 7 days). The data was processed with the program Felix (BIOSYM/Molecular Simulations, San Diego, CA), and the peak heights were fitted to an exponentially rising curve in order to obtain T, (regression: R>0.999).

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The powerful n-electron donor, tetrathiafulvalene, forms a strong green-coloured 1 : 1 complex with the n-electron accepting tetracationic cyclophane, cyclobis(Paraquat-p-phenylene), in both the solid and solution states as demonstrated by X-ray crystallography and spectroscopy (NMR and UV-VlS), respectively.

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