The achiral tetrapeptide Z‐Aib‐Aib‐Aib‐Gly‐OtBu

The title achiral peptide N‐benzyloxycarbonyl‐α‐aminoisobutyryl‐α‐aminoisobutyryl‐α‐aminoisobutyrylglycine tert‐butyl ester or Z‐Aib‐Aib‐Aib‐Gly‐OtBu (Aib is α‐aminoisobutyric acid, Z is benzyloxycarbonyl, Gly is glycine and OtBu indicates the tert‐butyl ester), C₂₆H₄₀N₄O₇, is partly hydrated (0.075H₂O) and has two different conformations which together constitute the asymmetric unit. Both molecules form incipient 3₁₀‐helices. They differ in the relative orientation of the N‐terminal protection group and at the C‐terminus. There are two 4→1 intramolecular hydrogen bonds.     

The peptide Z‐Aib‐Aib‐Aib‐L‐Ala‐OtBu

The title peptide, N‐benzyloxycarbonyl‐α‐aminoisobutyryl‐α‐aminoisobutyryl‐α‐aminoisobutyryl‐L‐alanine tert‐butyl ester or Z‐Aib‐Aib‐Aib‐L‐Ala‐OtBu (Aib is α‐aminoisobutyric acid, Z is benzyloxycarbonyl and OtBu indicates the tert‐butyl ester), C₂₇H₄₂N₄O₇, is a left‐handed helix with a right‐handed conformation in the fourth residue, which is the only chiral residue. There are two 4→1 intramolecular hydrogen bonds in the structure. In the lattice, molecules are hydrogen bonded to form columns along the c axis.     

Crystallographic report: The [bis(η5‐methylcyclopentadienyl)titanium(IV)‐bis(N‐methylglycine)] dichloride

The crystal network of [Cp′₂Ti(N?CH₃? Gly)₂]²⁺[Cl^?]₂ (Cp′ = (CH₃)C₅H₄) complex, which crystallizes as a solvate with CH₃OH, is built up with discrete cationic units connected through intermolecular H· · ·Cl bonds. The α‐amino acid ligands are attached through an intramolecular H· · ·O bond within one cationic unit. Copyright © 2004 John Wiley & Sons, Ltd.     

Conformational study of the 3,6‐dihydro‐2H‐1,4‐oxazin‐2‐one fragment in 8‐tert‐butyl‐7‐methoxy‐8‐methyl‐9‐oxa‐6‐azaspiro[4.5]decane‐2,10‐dione stereoisomers

Unnatural cyclic α‐amino acids play an important role in the search for biologically active compounds and macromolecules. Enantiomers of natural amino acids with a d configuration are not naturally encoded, but can be chemically synthesized. The crystal structures of two enantiomers obtained by a method of stereoselective synthesis, namely (5R ,8S )‐8‐tert‐butyl‐7‐methoxy‐8‐methyl‐9‐oxa‐6‐azaspiro[4.5]decane‐2,10‐dione, (1), and (5S ,8R )‐8‐tert‐butyl‐7‐methoxy‐8‐methyl‐9‐oxa‐6‐azaspiro[4.5]decane‐2,10‐dione, (2), both C₁₄H₂₁NO₄, were determined by X‐ray diffraction. Both enantiomers crystallize isostructurally in the space group P 2₁, with one molecule in the asymmetric unit and with the same packing motif. The crystal structures are stabilized by C—H…O hydrogen bonds, resulting in the formation of chains along the [100] and [010] directions. The conformation of the 3,6‐dihydro‐2H‐1,4‐oxazin‐2‐one fragment was compared with other crystal structures possessing this heterocyclic moiety. The comparison showed that the title compounds are not exceptional among structures containing the 3,6‐dihydro‐2H‐1,4‐oxazin‐2‐one fragment. The planar moiety was more frequently observed in derivatives in which this fragment was not condensed with other rings.     

The effect of amino acid backbone length on molecular packing: crystalline tartrates of glycine, β‐alanine, γ‐aminobutyric acid (GABA) and dl‐α‐aminobutyric acid (AABA)

We report a novel 1:1 cocrystal of β‐alanine with dl ‐tartaric acid, C₃H₇NO₂·C₄H₆O₆, (II), and three new molecular salts of dl ‐tartaric acid with β‐alanine {3‐azaniumylpropanoic acid–3‐azaniumylpropanoate dl ‐tartaric acid–dl ‐tartrate, [H(C₃H₇NO₂)₂]⁺·[H(C₄H₅O₆)₂]⁻, (III)}, γ‐aminobutyric acid [3‐carboxypropanaminium dl ‐tartrate, C₄H₁₀NO₂⁺·C₄H₅O₆⁻, (IV)] and dl ‐α‐aminobutyric acid {dl ‐2‐azaniumylbutanoic acid–dl ‐2‐azaniumylbutanoate dl ‐tartaric acid–dl ‐tartrate, [H(C₄H₉NO₂)₂]⁺·[H(C₄H₅O₆)₂]⁻, (V)}. The crystal structures of binary crystals of dl ‐tartaric acid with glycine, (I), β‐alanine, (II) and (III), GABA, (IV), and dl ‐AABA, (V), have similar molecular packing and crystallographic motifs. The shortest amino acid (i.e. glycine) forms a cocrystal, (I), with dl ‐tartaric acid, whereas the larger amino acids form molecular salts, viz. (IV) and (V). β‐Alanine is the only amino acid capable of forming both a cocrystal [i.e. (II)] and a molecular salt [i.e. (III)] with dl ‐tartaric acid. The cocrystals of glycine and β‐alanine with dl ‐tartaric acid, i.e. (I) and (II), respectively, contain chains of amino acid zwitterions, similar to the structure of pure glycine. In the structures of the molecular salts of amino acids, the amino acid cations form isolated dimers [of β‐alanine in (III), GABA in (IV) and dl ‐AABA in (V)], which are linked by strong O—H…O hydrogen bonds. Moreover, the three crystal structures comprise different types of dimeric cations, i.e. (A…A)⁺ in (III) and (V), and A⁺…A⁺ in (IV). Molecular salts (IV) and (V) are the first examples of molecular salts of GABA and dl ‐AABA that contain dimers of amino acid cations. The geometry of each investigated amino acid (except dl ‐AABA) correlates with the melting point of its mixed crystal.     

Novel N‐(2,2‐Dimethyl‐2H‐azirin‐3‐yl)‐L‐prolinates as Aib‐Pro Synthons

The syntheses of phenacyl N‐(2,2‐dimethyl‐2H‐azirin‐3‐yl)‐L ‐prolinate and allyl N‐(2,2‐dimethyl‐2H‐azirin‐3‐yl)‐L ‐prolinate are reported. Reactions of these 2H‐azirin‐3‐amine derivatives with Z‐protected amino acids have shown them to be suitable synthons for the Aib‐Pro unit in peptide synthesis. After incorporation into the peptide by means of the ‘azirine/oxazolone method’, the C‐termini of the resulting peptides were deprotected selectively with Zn in AcOH or by a mild Pd⁰‐promoted procedure, respectively.     

Synthesis of Z‐Protected Aib‐ and Phe(2Me)‐Containing Pentapeptides and Their Crystal Structures

A series of pentapeptide derivatives containing α,α‐disubstituted α‐amino acids have been prepared by a combination of the ‘azirine/oxazolone method’ and segment condensations. X‐Ray crystal‐structure determinations of the molecular structures confirmed the presence of helical conformations stabilized by β‐turns of type III or III′. Pentapeptides containing (R)‐Phe(2Me) form a right‐handed helix, whereas those containing (S)‐Phe(2Me) adopt a left‐handed helical structure.     

Synthesis,structural characterization and cytotoxic activity of diorganotin(IV) complexes of N‐(5‐halosalicylidene)‐α‐amino acid

Fourteen new diorganotin(IV) complexes of N‐(5‐halosalicylidene)‐α‐amino acid, R′₂Sn(5‐X‐2‐OC₆H₃CH?NCHRCOO) (where X = Cl, Br; R = H, Me, i‐Pr; R′ = n‐Bu, Ph, Cy), were synthesized by the reactions of diorganotin halides with potassium salt of N‐(5‐halosalicylidene)‐α‐amino acid and characterized by elemental analysis, IR and NMR (¹H, ¹³C and ¹¹⁹Sn) spectra. The crystal structures of Bu₂Sn(5‐Cl‐2‐OC₆H₃CH?NCH(i‐Pr)COO) and Ph₂Sn(5‐Br‐2‐OC₆H₃CH?NCH(i‐Pr)COO) were determined by X‐ray single‐crystal diffraction and showed that the tin atoms are in a distorted trigonal bipyramidal geometry and form five‐ and six‐membered chelate rings with the tridentate ligand. Bioassay results of a few compounds indicated that the compounds have strong cytotoxic activity against three human tumour cell lines, i.e. HeLa, CoLo205 and MCF‐7, and the activity decreased in the order Cy>n‐Bu>Ph for the R′ group bound to tin. Copyright © 2005 John Wiley & Sons, Ltd.     

Four oxoindole‐linked α‐alkoxy‐β‐amino acid derivatives

Four structures of oxoindolyl α‐hydroxy‐β‐amino acid derivatives, namely, methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐methoxy‐2‐phenylacetate, C₂₄H₂₈N₂O₆, (I), methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐ethoxy‐2‐phenylacetate, C₂₅H₃₀N₂O₆, (II), methyl 2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐[(4‐methoxybenzyl)oxy]‐2‐phenylacetate, C₃₁H₃₄N₂O₇, (III), and methyl 2‐[(anthracen‐9‐yl)methoxy]‐2‐{3‐[(tert‐butoxycarbonyl)amino]‐1‐methyl‐2‐oxoindolin‐3‐yl}‐2‐phenylacetate, C₃₈H₃₆N₂O₆, (IV), have been determined. The diastereoselectivity of the chemical reaction involving α‐diazoesters and isatin imines in the presence of benzyl alcohol is confirmed through the relative configuration of the two stereogenic centres. In esters (I) and (III), the amide group adopts an anti conformation, whereas the conformation is syn in esters (II) and (IV). Nevertheless, the amide group forms intramolecular N—H...O hydrogen bonds with the ester and ether O atoms in all four structures. The ether‐linked substituents are in the extended conformation in all four structures. Ester (II) is dominated by intermolecular N—H...O hydrogen‐bond interactions. In contrast, the remaining three structures are sustained by C—H...O hydrogen‐bond interactions.     

Conformation of a terminally protected βγ hybrid dipeptide Boc‐Ant‐Gpn‐OMe stabilized by C6/C7 hydrogen bonds

The hybrid βγ dipeptide, methyl 2‐[1‐({2‐[(tert‐butoxycarbonyl)amino]benzamido}methyl)cyclohexyl]acetate (Boc‐Ant‐Gpn‐OMe), C₂₂H₃₂N₂O₅, adopts a folded conformation stabilized by intramolecular six‐ (C₆) and seven‐membered (C₇) hydrogen‐bonded rings, together with weak C—H...O and C—H...π interactions, resulting in a ribbon‐like structure.     

π‐stacking and C—X...D (X = H,NO2; D = O, π) interactions in the crystal network of both C—H...N and π‐stacked dimers of 1,2‐bis(4‐bromophenyl)‐1H‐benzimidazole and 2‐(4‐bromophenyl)‐1‐(4‐nitrophenyl)‐1H‐benzimidazole

Molecules of 1,2‐bis(4‐bromophenyl)‐1H‐benzimidazole, C₁₉H₁₂Br₂N₂, (I), and 2‐(4‐bromophenyl)‐1‐(4‐nitrophenyl)‐1H‐benzimidazole, C₁₉H₁₂BrN₃O₂, (II), are arranged in dimeric units through C—H...N and parallel‐displaced π‐stacking interactions favoured by the appropriate disposition of N‐ and C‐bonded phenyl rings with respect to the mean benzimidazole plane. The molecular packing of the dimers of (I) and (II) arises by the concurrence of a diverse set of weak intermolecular C—X...D (X = H, NO₂; D = O, π) interactions.     

A new one‐dimensional nickel metal–organic framework: catena‐poly[[[diaquabis(4‐{[(1‐phenyl‐1H‐tetrazol‐5‐yl)sulfanyl]methyl}benzoato‐κO)nickel(II)]‐μ‐4,4′‐bipyridine‐κ2N:N′] monohydrate]

The title complex, {[Ni(C₁₅H₁₁N₄O₂S)₂(C₁₀H₈N₂)(H₂O)₂]·H₂O}_n, was synthesized by the reaction of nickel chloride, 4‐{[(1‐phenyl‐1H‐tetrazol‐5‐yl)sulfanyl]methyl}benzoic acid (HL) and 4,4′‐bipyridine (bpy) under hydrothermal conditions. The asymmetric unit contains two half Ni^II ions, each located on an inversion centre, two L⁻ ligands, one bpy ligand, two coordinated water molecules and one unligated water molecule. Each Ni^II centre is six‐coordinated by two monodentate carboxylate O atoms from two different L⁻ ligands, two pyridine N atoms from two different bpy ligands and two terminal water molecules, displaying a nearly ideal octahedral geometry. The Ni^II ions are bridged by 4,4′‐bipyridine ligands to afford a linear array, with an Ni...Ni separation of 11.361 (1) Å, which is further decorated by two monodentate L⁻ ligands trans to each other, resulting in a one‐dimensional fishbone‐like chain structure. These one‐dimensional fishbone‐like chains are further linked by O—H...O, O—H...N and C—H...O hydrogen bonds and π–π stacking interactions to form a three‐dimensional supramolecular architecture. The thermal stability of the title complex was investigated via thermogravimetric analysis.     

C 5 and C7 intramolecular hydrogen bonds stabilize the structure of N‐pyrazinoyl‐gabapentin (Pyr‐Gpn‐OH)

2‐{1‐[(Pyrazin‐2‐ylformamido)methyl]cyclohexyl}acetic acid (Pyr‐Gpn‐OH), C₁₄H₁₉N₃O₃, is an N‐protected derivative of gabapentin (Gpn). The compound crystallizes in the triclinic space group P and the molecular conformation is stabilized by intramolecular five‐ (C₅) and seven‐membered (C₇) hydrogen‐bonded rings. The packing of the molecules reveals intermolecular O—H...O and C—H...N hydrogen bonds, together with π–π interactions.     

Three different fluoro‐ or chloro‐substituted 1′‐deoxy‐1′‐phenyl‐β‐D‐ribofuranoses

Crystal structures are reported for three fluoro‐ or chloro‐substituted 1′‐deoxy‐1′‐phenyl‐β‐D‐ribofuranoses, namely 1′‐deoxy‐1′‐(2,4,5‐trifluorophenyl)‐β‐D‐ribofuranose, C₁₁H₁₁F₃O₄, (I), 1′‐deoxy‐1′‐(2,4,6‐trifluorophenyl)‐β‐D‐ribofuranose, C₁₁H₁₁F₃O₄, (II), and 1′‐(4‐chlorophenyl)‐1′‐deoxy‐β‐D‐ribofuranose, C₁₁H₁₃ClO₄, (III). The five‐membered furanose ring of the three compounds has a conformation between a C2′‐endo,C3′‐exo twist and a C2′‐endo envelope. The ribofuranose groups of (I) and (III) are connected by intermolecular O—H...O hydrogen bonds to six symmetry‐related molecules to form double layers, while the ribofuranose group of (II) is connected by O—H...O hydrogen bonds to four symmetry‐related molecules to form single layers. The O...O contact distance of the O—H...O hydrogen bonds ranges from 2.7172 (15) to 2.8895 (19) Å. Neighbouring double layers of (I) are connected by a very weak intermolecular C—F...π contact. The layers of (II) are connected by one C—H...O and two C—H...F contacts, while the double layers of (III) are connected by a C—H...Cl contact. The conformations of the molecules are compared with those of seven related molecules. The orientation of the benzene ring is coplanar with the H—C1′ bond or bisecting the H—C1′—C2′ angle, or intermediate between these positions. The orientation of the benzene ring is independent of the substitution pattern of the ring and depends mainly on crystal‐packing effects.     

Synthesis,structural characterization and cytotoxic activity of diorganotin(IV) complexes of N‐(5‐halosalicylidene)tryptophane

Four new diorganotin(IV) complexes of N‐(5‐halosalicylidene)tryptophane, R₂Sn[5‐X‐2‐OC₆H₃CH?NCH(CH₂Ind)COO] [Ind = 3‐indolyl; R, X = Et, Cl ( 1 ); Et, Br( 2 ); n‐Bu, Cl ( 3 ); n‐Bu, Br ( 4 )], were synthesized and characterized by elemental analysis, IR and NMR (¹H, ¹³C and ¹¹⁹Sn) spectra. The crystal structures of complexes 1 – 3 were determined by X‐ray single crystal diffraction and showed that the tin atoms are in a distorted trigonal bipyramidal geometry and form five‐ and six‐membered chelate rings with the tridentate ligand. Intermolecular weak interactions in 1–3 link molecules, respectively, into a two‐dimensional array, a one‐dimensional infinite chain and a one‐dimensional double‐chain supramolecular structure. Bioassay results of the compounds indicated that the dibutyltin complexes 3 and 4 have potent in vitro cytotoxic activity against two human tumor cell lines, CoLo205 and Bcap37, while the diethyltin complexes 1 and 2 display weak cytotoxic activity. Copyright © 2008 John Wiley & Sons, Ltd.     

The six‐membered‐ring azomethine N‐((E)‐{5‐[(E)‐(pyridin‐3‐ylimino)methyl]thiophen‐2‐yl}methylidene)pyridin‐3‐amine

The title compound, C₁₆H₁₂N₄S, forms a three‐dimensional layered network structure via intermolecular hydrogen bonding and π‐stacking. The azomethine molecule adopts the thermodynamically stable E regioisomer and the pyridine substituents are antiperiplanar. The mean planes of the pyridine rings and the azomethine group to which they are connected are twisted by 27.27 (5) and 33.60 (5)°. The electrochemical energy gap of 2.3 eV based on the HOMO–LUMO energy difference is in agreement with the spectroscopically derived value.     

Two Fe3(μ3‐S)2(CO)8 clusters with terminal N‐heterocyclic carbenes

The title compounds with terminal N‐heterocyclic carbenes, namely octacarbonyl(imidazolidinylidene‐κC²)di‐μ₃‐sulfido‐triiron(II)(2 Fe—Fe), [Fe₃(C₃H₆N₂)(μ₃‐S)₂(CO)₈], (I), and octacarbonyl(1‐methylimidazo[1,5‐a]pyridin‐3‐ylidene‐κC³)di‐μ₃‐sulfido‐triiron(II)(2 Fe—Fe), [Fe₃(C₈H₈N₂)(μ₃‐S)₂(CO)₈], (II), have been synthesized. Each compound contains two Fe—Fe bonds and two S atoms above and below a triiron triangle. One of the eight carbonyl ligands deviates significantly from linearity. In (I), dimers generated by an N—H...S hydrogen bond are linked into [001] double chains by a second N—H...S hydrogen bond. These chains are packed by a C—H...O hydrogen bond to yield [101] sheets. In (II), dimers generated by an N—H...S hydrogen bond are linked by C—H...O hydrogen bonds to form [111] double chains.     

A New Route to N‐Aryl 2‐Alkenamides,N‐Allyl N‐Aryl 2‐Alkenamides,and N‐Aryl α,β‐Unsaturated γ‐Lactams from N‐Aryl 3‐(Phenylsulfonyl)propanamides

A series of N‐aryl 2‐alkenamides were produced efficiently by treating N‐aryl 3‐(phenylsulfonyl)‐propanamides with potassium tert‐butoxide in THF at 0°C. With out isolation, it was further treated with an additional equivalent of potassium tert‐butoxide and allyl bromide to give N‐allyl N‐aryl 2‐alkenamides in one pot in good yields. Followed by a ring‐closing metathesis reaction, these N‐allyl N‐aryl 2‐alkenamides were respectively converted into corresponding N‐aryl α,β‐unsaturated γ‐lactams in moderate yields.     

A copper(I) coordination polymer incorporation the corrosion inhibitor 1H‐benzotriazole: poly[μ3‐benzotriazolato‐κ3N1:N2:N3‐copper(I)]

The title complex, [Cu(C₆H₄N₃)]_n, was synthesized by the reaction of cupric nitrate, 1H‐benzotriazole (BTAH) and aqueous ammonia under hydrothermal conditions. The asymmetric unit contains three crystallographically independent Cu^I cations and two 1H‐benzotriazolate ligands. Two of the Cu^I cations, one with a linear two‐coordinated geometry and one with a four‐coordinated tetrahedral geometry, are located on sites with crystallographically imposed twofold symmetry. The third Cu^I cation, with a planar three‐coordinated geometry, is on a general position. Two Cu^I cations are doubly bridged by two BTA⁻ ligands to afford a noncentrosymmetric planar [Cu₂(BTA)₂] subunit, and two [Cu₂(BTA)₂] subunits are arranged in an antiparallel manner to form a centrosymmetric [Cu₂(BTA)₂]₂ secondary building unit (SBU). The SBUs are connected in a crosswise manner via the sharing of four‐coordinated Cu^I cations, Cu—N bonding and bridging by two‐coordinate Cu^I cations, resulting in a one‐dimensional chain along the c axis. These one‐dimensional chains are further linked by C—H...π and weak van der Waals interactions to form a three‐dimensional supramolecular architecture.