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1.  [CrIII8MII6]12+ Coordination Cubes (MII=Cu, Co)** 
[CrIII8MII6]12+ (MII=Cu, Co) coordination cubes were constructed from a simple [CrIIIL3] metalloligand and a “naked” MII salt. The flexibility in the design proffers the potential to tune the physical properties, as all the constituent parts of the cage can be changed without structural alteration. Computational techniques (known in theoretical nuclear physics as statistical spectroscopy) in tandem with EPR spectroscopy are used to interpret the magnetic behavior.
PMCID: PMC4471575  PMID: 25891167
EPR spectroscopy; heterometallic cages; magnetometry; molecular magnetism; transition metals
2.  Crystal structure of 2-hydroxy-N-(2-hydroxyethyl)-N-{2-hydroxy-3-[(E)-N-hydroxyethanimidoyl]-5-methylbenzyl}ethanaminium acetate monohydrate 
The structure of the title hydrated mol­ecular salt, C14H23N2O4 +·C2H3O2 −·H2O, was determined as part of a wider study on the use of the mol­ecule as a polydentate ligand in the synthesis of MnIII clusters with magnetic properties. The cation features intra­molecular O—H⋯N and N—H⋯O hydrogen-bond inter­actions. The crystal structure features a range of inter­molecular hydrogen-bonding inter­actions, principally O—H⋯O inter­actions between all three species in the asymmetric unit. An R 2 4(8) graph-set hydrogen-bonding motif between the anion and water mol­ecules serves as a unit which links to the cation via the di­ethano­lamine group. Each O atom of the acetate anion accepts two hydrogen bonds.
PMCID: PMC4350734  PMID: 25844240
crystal structure; hydrogen bonding; hydrate; organic salt; magnetism
3.  Synthesis and Crystallographic Study of N′-(1-benzylpiperidin-4-yl)acetohydrazide 
Journal of chemical crystallography  2010;40(11):961-964.
As part of a study into new Fentanyl-derived opioid compounds with potent analgesic activity and reduced side effects the starting material title compound, C14H21N3O (1), was synthesized and characterized by NMR spectroscopy and single-crystal X-ray diffraction. The crystal structure is monoclinic Cc with unit cell parameters a = 14.1480(3) Å, b = 14.1720(4) Å, c = 27.6701(7) Å, β = 96.956(1)°, α = γ = 90°. The compound has crystallized with four crystallographically unique molecules in the asymmetric unit; each molecule has a very similar conformation and an analysis of the structure shows that although all four unique molecules overlay very well there is no evidence of pseudo-symmetry which would relate the molecules in the higher symmetry space group C2/c. The crystal packing consists of two separate hydrogen bonded chains which are linked together to form a thick 2D structure in the ab plane.
PMCID: PMC4260262  PMID: 25505832
Organic compounds; Z′ > 1; Hydrogen bonding
4.  Proton sharing and transfer in some zwitterionic compounds based on 4-oxo-4-((1-phenethylpiperidin-4-yl)(phenyl)amino)alcanoic acids† 
CrystEngComm / RSC  2010;12(11):3651-3657.
Three compounds, each derived from Fentanyl and differing essentially only in the length of a carboxylic acid chain, were synthesized and yielded four crystal structures three of which share several structural similarities, including the length of the chain, while the fourth, with a shorter chain, is quite different. The chain length has a significant influence on the crystal structures formed. The ‘three atom’ chain compounds are all solvated zwitterions which feature a hydrogen-bonded ‘dimer’ between adjacent zwitterions. The formation of this large dimer leaves available a second carboxylate O atom to take part in hydrogen bonding interactions with solvent molecules. The shorter ‘two atom’ chain compound was difficult to crystallize and required the use of synchrotron radiation to measure X-ray diffraction data. It does not form the same dimer motif observed in the ‘three atom’ chain compounds and has not formally formed a zwitterion; although there is evidence of proton sharing or disorder X-ray data are insufficient to create a disordered model, and the compound was modeled as formally neutral based on O–H and N–H distances. Room temperature analyses showed the proton transfer behavior to be independent of crystal temperature, and nuclear magnetic resonance studies show proton transfer behavior in solution. The formation of a zwitterionic hydrogen-bonded dimer is implicated in providing some stability during crystal growth of the easily crystallized ‘three atom’ chain compounds.
PMCID: PMC4241297  PMID: 25425961
5.  Synthesis and biological evaluation of new opioid agonist and neurokinin-1 antagonist bivalent ligands 
Bioorganic & medicinal chemistry  2011;19(20):6135-6142.
Newly designed bivalent ligands—opioid agonist/NK1-antagonists have been synthesized. The synthesis of new starting materials—carboxy-derivatives of Fentanyl (1a–1c) was developed. These products have been transformed to ‘isoimidium perchlorates’ (2a–c). The new isoimidium perchlorates have been successfully implemented in nucleophilic addition reactions, with L-tryptophan 3,5-bis(trifluoromethyl)benzyl ester to give the target compounds—amides (3a–c). Perchlorates (2a–c) successfully undergo reactions with other nucleophiles such as alcohols, amines or hydrazines. The obtained compound 3b exhibited μ-opioid agonist activity and NK1-antagonist activity and may serve as a useful lead compound for the further design of a new series of opioid agonist/NK1-antagonist compounds.
PMCID: PMC4137774  PMID: 21925887
Analgesic; Bivalent ligands; μ-Opioids; NK1 antagonist; Fentanyl
6.  Hydrazine-mediated cyclization of Ugi products to synthesize novel 3-hydroxypyrazoles 
Tetrahedron letters  2012;53(21):2592-2594.
This report discloses a novel concise synthesis of a series of 3-hydroxypyrazoles 5 via a tandem Ugi/debenzylation /hydrazine-mediated cyclization sequence. Herein, n-butyl isocyanide 4b was utilized as an alternative to classical convertible isocyanides enabling high yielding hydrazine-mediated cyclization. Taken together, a novel class of 3-hydroxypyrazoles 5a–5i was synthesized with potential to be of interest in future library enrichment strategies.
PMCID: PMC3337763  PMID: 22544981
Multicomponent reaction; Ugi reaction; 3-hydroxypyrazole; hydrazine-mediated cyclization
7.  Concise route to a series of novel 3-(tetrazol-5-yl)quinoxalin-2(1H)-ones 
Tetrahedron letters  2012;53(13):1664-1667.
This report presents a novel three step solution phase protocol to synthesize 3-(tetrazol-5-yl)quinoxalin-2(1H)-ones. The strategy utilizes ethyl glyoxalate and mono-N-Boc-protected-o-phenylenediamine derivatives in the Ugi-Azide multi-component reaction (MCR) to generate a unique 1,5-disubstituted tetrazole. Subsequent acid treatment stimulates a simultaneous Boc deprotection and intramolecular cyclization leading to bis-3,4-dihydroquinoxalinone tetrazoles. Direct oxidation using a stable solid-phase radical catalyst (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO) with ceric ammonium nitrate (CAN) in catalytic fashion initiating aerobic oxidation, completes the entire procedure to generate a series of original unique bis-quinoxalinone tetrazoles. The method was also expanded to produce a bis-benzodiazepine tetrazole.
PMCID: PMC3374393  PMID: 22707799
8.  On the Synthesis of 1,4,7-Tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane† 
Tetrahedron letters  2011;52(17):2058-2061.
1,4,7-Tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane is widely used as an intermediate in the preparation of medically important DO3A and DOTA metal chelators. Despite its commercial availability and importance, the literature describing the preparation and properties of the free base is limited and sometimes unclear. We present herein an efficient synthesis of the hydrobromide salt of 1,4,7-tris(tert-butoxycarbonylmethyl)-1,4,7,10-tetraazacyclododecane, characterize this compound spectroscopically and by X-ray crystallographic analysis, describe its simple conversion to the corresponding free base, characterize this compound spectroscopically and by X-ray crystallographic analysis, and make observations on the reactivity of this interesting and useful compound.
PMCID: PMC3079211  PMID: 21516221
Synthesis; DOTA; DO3A; Contrast Agent; MRI; X-ray crystallography
9.  Facile, novel two-step syntheses of benzimidazoles, bis-benzimidazoles, and bis-benzimidazole-dihydroquinoxalines 
Molecular Diversity  2012;16(1):73-79.
Three scaffolds of benzimidazoles, bis-benzimidazoles, and bis-benzimidazole-dihydroquinoxalines were synthesized via Ugi/de-protection/cyclization methodology. Benzimidazole forming ring closure was enabled under microwave irradiation in the presence of 10% TFA/DCE. The methodology demonstrates the utility of 2-(N-Boc-amino)-phenyl-isocyanide for the generation of new molecular diversity.
PMCID: PMC3311162  PMID: 22237832
UDC; Multi-component reactions (MCRs); Benzimidazoles; Bis-benzimidazoles; Bis-benzimidazole-dihydroquinoxalines
10.  [2-Butyl-4-(4-tert-butyl­benz­yl)-1,2,4-triazol-3-yl­idene]chlorido[(1,2,5,6-η)-cyclo­octa-1,5-diene]iridium(I) 
In the title compound, [IrCl(C8H12)(C17H25N3)], the IrI ion has a distorted square-planar coordination geometry. The N-heterocyclic carbene ligand has an extended S-shaped conformation. The butyl group was refined using a two-part 1:1 disorder model. In the crystal, three unique weak C—H⋯Cl contacts are present. Two of these form a motif described as R 2 1(6) in graph-set notation, while a third forms an R 2 2(8) motif about a crystallographic inversion center. The result is a chain structure which extends parallel to the crystallographic a axis.
PMCID: PMC3274890  PMID: 22346837
11.  [(1,2,5,6-η)-Cyclo­octa-1,5-diene]bis­(1-isopropyl-3-methyl­imidazolin-2-yl­idene)rhodium(I) tetra­fluorido­borate 
In the title compound, [Rh(C8H12)(C7H12N2)2]BF4, the square-planar Rh complex cation and the BF4 − anion are both bis­ected by a crystallographic twofold rotation axis. The Rh and B atoms lie on this axis and all others are in general positions. In the crystal, two unique C—H⋯F hydrogen-bonding inter­actions are present, which involve both imidazolin-2-yl­idene H atoms. They form two separate C(5) motifs, the combination of which is a rippled hydrogen-bonded sheet structure in the ab plane.
PMCID: PMC3238752  PMID: 22199629
12.  3-[4-(10H-Indolo[3,2-b]quinolin-11-yl)piperazin-1-yl]propan-1-ol 
In the title compound, C22H24N4O, the aromatic moiety is essentially planar (r.m.s. deviation of a least-squares plane fitted through all non-H atoms = 0.0386 Å) and is rotated by 89.98 (4)° from the piperazine ring, which adopts the expected chair conformation. The propanol chain is not fully extended away from the piperazine ring. In the crystal, there are two unique hydrogen-bonding inter­actions. One is an O—H⋯N inter­action which, together with an inversion-related symmetry equivalent, forms a ring motif. The second is an N—H⋯N inter­action which links adjacent mol­ecules by means of a chain motif which propagates in the c-axis direction. Overall, a two-dimensional hydrogen-bonded structure is formed.
PMCID: PMC3239093  PMID: 22199941
13.  Design, Synthesis, and Evaluation of 1,4,7,10-Tetraazacyclododecane-1,4,7-triacetic Acid-Derived, Redox-Sensitive Contrast Agents for Magnetic Resonance Imaging 
Journal of medicinal chemistry  2010;53(18):6747-6757.
The design and synthesis of three 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) derivatives bearing linkers with terminal thiol groups and a preliminary evaluation of their potential for use in assembling redox-sensitive Magnetic Resonance Imaging (MRI) contrast agents are reported. The linkers were selected based on computational docking with a crystal structure of human serum albumin (HSA). Gd(III)-DO3A and Eu(III)-DO3A complexes were synthesized, and the structure of one complex was established by X-ray crystallographic analysis. The binding to HSA of a Gd(III)-DO3A complex bearing a thiol-terminated 3,6-dioxanonyl chain was competitively inhibited by homocysteine and by the corresponding Eu chelate. Binding to HSA was abolished when the terminal thiol group of this complex was absent. The longitudinal water-proton relaxivities (r1) of the three Gd(III)-DO3A complexes and of two Gd(III)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) complexes were measured in saline at 7 Tesla. The DO3A complexes exhibited smaller r1 values, in both bound and free states, than the DOTA complexes.
PMCID: PMC2941433  PMID: 20722424
14.  Concise Preparation of Novel Tricyclic Chemotypes: Fused Hydantoin-benzodiazepines 
Tetrahedron letters  2010;51(36):4689-4692.
The following article describes a concise synthesis of a collection of 4,5-dihydro-1H-benzo[e][1,4]diazepines fused to a hydantoin ring. Molecular complexity and biological relevance is high and structures are generated in a mere three steps, employing the Ugi reaction to assemble diversity reagents. The protocol represents a novel UDC (Ugi-deprotect-cyclize) strategy employed in the Ugi-5-component CO2 mediated condensation, followed by further cyclization under basic conditions, to afford the fused hydantoin. Mechanistic caveats, dependent on aldehydes of choice will be revealed and a facile oxidation of final products to imidazolidenetriones briefly discussed.
PMCID: PMC2928152  PMID: 20802841
15.  3-(2,6-Dimethyl­anilino)imidazo[1,2-a]pyridin-1-ium perchlorate 
The structure of the organic cation in the title compound, C15H16N3 +·ClO4 −, contains two essentially planar rings. Mean planes fitted through all non-H atoms of each ring system have an r.m.s. deviation of 0.019 Å for the imidazole-based ring and 0.016 Å for the 2,6-dimethyl­phenyl ring. The angle between the two planes is 86.76 (2)°. In the crystal structure, N—H⋯O inter­actions form a one-dimensional chain, which propagates in the b-axis direction. C—H⋯O inter­actions are also found in the crystal packing.
PMCID: PMC3089197  PMID: 21754522
16.  N,N′-Bis(5-bromo­pyridin-2-yl)methane­diamine 
The V-shaped title compound, C11H10Br2N4, lies on a crystallographic twofold rotation axis which passes through the central C atom. In the crystal, an infinite tape motif, which propagates in the a-axis direction, is formed by inversion-related N—H⋯N hydrogen-bonding inter­actions. The structure confirmed the identity of the compound as a reaction side product.
PMCID: PMC3099949  PMID: 21754117
17.  Enantioselective organocatalytic α-sulfenylation of substituted diketopiperazines 
Tetrahedron, asymmetry  2009;20(23):2742-2750.
The asymmetric organocatalytic α-sulfenylation of substituted piperazine-2,5-diones is reported, with cinchona alkaloids as chiral Lewis bases and electrophilic sulfur transfer reagents. Catalyst loadings, the type of sulfur transfer reagent, temperature and solvent were investigated in order to optimize the reaction conditions. The effects of ring substitution and the type of catalyst on the yield and enantioselectivity of the reaction are reported.
PMCID: PMC2811878  PMID: 20161615
18.  4-(Piperidin-1-yl)-4H-benzo[b]tetra­zolo[1,5-d][1,4]diazepin-5(6H)-one 
There are two crystallographically unique mol­ecules present in the asymmetric unit of the title compound, C14H16N6O; in both mol­ecules, the seven-membered diazepinone ring adopts a boat-like conformation and the chair conformation piperidine ring is an axial substituent on the diazepinone ring. In the crystal, each mol­ecule forms hydrogen bonds with its respective symmetry equivalents. Hydrogen bonding between mol­ecule A and symmetry equivalents forms two ring motifs, the first formed by inversion-related N—H⋯O inter­actions and the second formed by C—H⋯O and C—H⋯N inter­actions. The combination of both ring motifs results in the formation of an infinite double tape, which propagates in the a-axis direction. Hydrogen bonding between mol­ecule B and symmetry equivalents forms one ring motif by inversion-related N—H⋯O inter­actions and a second ring motif by C—H⋯O inter­actions, which propagate as a single tape parallel with the c axis.
PMCID: PMC3050344  PMID: 21522729
19.  (S)-Methyl 2-{(S)-2-[bis­(4-meth­oxy­phen­yl)methyl­idene­amino]-3-hy­droxy­propanamido}-3-methyl­butano­ate 
The title compound, C24H30N2O6, a Schiff base, adopts an extended conformation in which the meth­oxy groups are essentially coplanar with the aromatic ring to which they are bonded (mean planes fitted through the non-H atoms of each methoxyphenyl group have r.m.s. deviations of 0.078 and 0.044 Å) and the angle between mean planes fitted through the aromatic rings is 87.57 (10)°. An intra­molecular N—H⋯N hydrogen bond keeps the imine and amide groups essentially coplanar. A mean plane fitted through these groups has an r.m.s. deviation of 0.0545 Å. Additional O—H⋯O hydrogen bonding parallel with the a axis links the mol­ecules into a hydrogen-bonded chain in the crystal. C—H⋯O and C—H⋯π inter­actions are found within the crystal packing. The compound has been assigned the S,S configuration on the basis of the chemical synthesis, which used pure homotopic l-amino acids, and we have no reason to believe that the compound has epimerized.
PMCID: PMC3050411  PMID: 21522640
20.  [(1,2,5,6-η)-1,5-Cyclo­octa­diene](1-isopropyl-3-methyl­imidazolin-2-yl­idene)(triphenyl­phosphine)iridium(I) tetra­fluorido­borate dichloro­methane solvate 
In the title compound, [Ir(C8H12)(C7H12N2)(C18H15P)]BF4·CH2Cl2, the Ir(I) atom has a square-planar conformation with normal bond lengths. One of the phenyl rings, and the solvent dichloro­methane mol­ecule, were refined using separate two part disorder models, each in an approximately 1:1 ratio.
PMCID: PMC3008037  PMID: 21588520
21.  Polymorphism and phase transition behavior of 6,6′-bis­(chloro­meth­yl)-1,1′,4,4′-tetra­methyl-3,3′-(p-phenyl­enedimethyl­ene)bis­(piperazine-2,5-dione) 
A crystallographic investigation of the title compound, C22H28Cl2N4O4, using crystals obtained under different crystallization conditions, revealed the presence of two distinct polymorphic forms. The mol­ecular conformation in the two polymorphs is very different: one adopts a ‘C’ shape, whereas the other adopts an ‘S’ shape. In the latter, the molecule lies across a crystallographic twofold axis. The ‘S’-shaped polymorph undergoes a reversible ortho­rhom­bic-to-monoclinic phase transition on cooling, whereas the structure of the ‘C’-shaped polymorph is temperature insensitive.
PMCID: PMC2720150  PMID: 19652319
22.  Efficient Organocatalytic α-Sulfenylation of Substituted Piperazine-2,5-diones 
Tetrahedron letters  2009;50(30):4310-4313.
Organocatalytic α-sulfenylation of substituted piperazine-2,5-diones is reported through the use of cinchona alkaloids as Lewis bases and electrophilic sulfur transfer reagents. 1-Phenylsulfanyl[1,2,4]triazole, a novel sulfur transfer reagent, gave excellent product yields with a number of substituted piperazine-2,5-diones under mild conditions. Catalyst loading, stoichiometry of sulfur electrophile, temperature and solvent were optimized to achieve high product yields.
PMCID: PMC2699310  PMID: 20161311
23.  Synthesis and investigations of double-pharmacophore ligands for treatment of chronic and neuropathic pain 
Bioorganic & medicinal chemistry  2009;17(14):5044-5053.
Acids 9 a–f as possible bivalent ligands designed as a structural combination of opioid μ-agonist (Fentanyl) and NSAID (Indomethacin) activities and produced compounds which were tested as analgesics. The obtained series of compounds exhibits low affinity and activity both at opioid receptors and as cyclooxygenase (COX) inhibitors. One explanation of the weak opioid activity could be stereochemical peculiarities of these bivalent compounds which differ significantly from the fentanyl skeleton. The absence of significant COX inhibitory properties could be explained by the required substitution of an acyl fragment in the indomethacin structure for 4-piperidyl.
PMCID: PMC2759397  PMID: 19540763
24.  3-[1-(4-Sulfamoylphen­yl)-5-p-tolyl-1H-pyrazol-3-yl]propanoic acid and 3-[5-(4-bromo­phen­yl)-1-(4-sulfamoyl­phen­yl)-1H-pyrazol-3-yl]­propanoic acid–dichloro­methane–diethyl ether–water (2/0.72/1/1) 
The syntheses of 3-[1-(4-sulfamoylphenyl)-5-p-tolyl-1H-pyra­zol-3-yl]propanoic acid, C19H19N3O4S, (I), and 3-[5-(4-bromo­phen­yl)-1-(4-sulfamoyl­phen­yl)-1H-pyrazol-3-yl]­propanoic acid–dichloro­methane–diethyl ether–water (2/0.72/1/1), 2C18H16BrN3O4S·0.72CH2Cl2·C4H10O·H2O, (II), are regio­specific. However, correct identification by spectroscopic techniques of the regioisomer formed is not trivial and single-crystal X-ray analysis provided the only means of unambiguous structure determination. Both structures make extensive use of hydrogen bonding and while compound (I) forms a straightforward unsolvated Z′ = 1 structure, compound (II) crystallizes as an unusual mixed solvate, with two crystallographically unique mol­ecules of the pyrazole derivative present in the asymmetric unit. The structure of (II) also features Br⋯Br inter­actions.
PMCID: PMC2724996  PMID: 19498242
25.  3-[5-(4-Chloro­phen­yl)-1-(4-methoxy­phen­yl)-1H-pyrazol-3-yl]propionic acid and the corresponding methyl ester 
The synthesis of 3-[5-(4-chloro­phen­yl)-1-(4-methoxy­phen­yl)-1H-pyrazol-3-yl]propionic acid, C19H17ClN2O3, (I), and its corresponding methyl ester, methyl 3-[5-(4-chloro­phen­yl)-1-(4-methoxy­phen­yl)-1H-pyrazol-3-yl]propionate, C20H19ClN2O3, (II), is regiospecific. However, correct identification of the regioisomer formed by spectroscopic techniques is not trivial and single-crystal X-ray analysis provided the only means of unambiguous structure determination. Compound (I) crystallizes with Z′ = 2. The propionic acid groups of the two crystallographically unique mol­ecules form a hydrogen-bonded dimer, as is typical of carboxylic acid groups in the solid state. Conformational differences between the meth­oxy­benzene and pyrazole rings give rise to two unique mol­ecules. The structure of (II) features just one mol­ecule in the asymmetric unit and the crystal packing makes greater use than (I) of weak C—H⋯A inter­actions, despite the lack of any functional groups for classical hydrogen bonding.
PMCID: PMC2724994  PMID: 19346614

Results 1-25 (34)