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Anthony Linden

Publications and source records attributed to Anthony Linden.

At least 37 records · Page 2Linked to original sources
PubMed2004

Anion mediated structural motifs in silver(I) complexes with corannulene.

The synthesis of three new silver(I) complexes with corannulene is reported. In the crystal these complexes form extended networks of Ag(+) ions, corannulene nuclei, and counterions, similar to the networks reported for Ag(+) with other polynuclear aromatic hydrocarbons (PAHs). The preferred Ag(+)-arene interaction is compared with the model developed by Kochi. The crystal motifs can be described by a classification scheme analogous to that developed by Etter for hydrogen-bonded networks in solids. The effect of counterion variation (ClO(4)(-), O(3)SCF(3)(-), BF(4)(-)) is noted to be substantial. Thus, although one can categorize the various networks, it is hard to predict an expected packing pattern on the basis of preferred binding in the metal/organic complex alone.

Journal Article↗
PubMed2004

Synthesis of type II beta-turn surrogate dipeptides based on syn-alpha-amino-alpha,beta-dialkyl-beta-lactams.

The achiral bis(trimethylsilyl)methyl group acts as an efficient stereochemical determinant of the alpha-alkylation reaction in beta-branched alpha-phenyloxazolidinyl- or alpha-diphenyloxazolidinyl-beta-lactams and provides the first stereocontrolled access to syn-alpha-amino-alpha,beta-dialkyl(aryl)-beta-lactams. These products are readily transformed into type II beta-turn mimetic surrogates 2B. [reaction: see text]

Alkylation↗
PubMed2004

Bis(1-chloro-2,2,4,4-tetramethyl-3-oxocyclobutan-1-yl)pentasulfane: an occupancy modulated structure.

The title compound crystallizes in the space group P2(1)/n and may be described by a partial ordering of a 1:1 disordered P2(1)/a parent structure with the c axis halved. The pentasulfane chain completes a full turn of a helix, which gives molecules containing left- or right-handed helices similar spatial requirements and allows them to be interchanged. The structure can be redescribed as containing 0.732 (1) of an ordered P2(1)/n structure and 0.268 (1) of a 1:1 disordered P2(1)/a structure, implying that 0.134 (1) of the molecule sites contain molecules of the opposite hand to that predicted by an ordered P2(1)/n structure. It is found that the average molecular position in the asymmetric unit is not the same for each component and that these structural differences must be recognized to obtain a satisfactory refinement.

Journal Article↗
PubMed2004

A practical total synthesis of hapalosin, a 12-membered cyclic depsipeptide with multidrug resistance-reversing activity, by employing improved segment coupling and macrolactonization.

A practical total synthesis of hapalosin, a compound with multidrug resistance-reversing activity, has been carried out using an unprecedented macrolactonization strategy. One of the features of the new approach is the straightforward and fully stereocontrolled access to the key gamma-amino beta-hydroxy carboxylic acid subunit via an efficient acetate aldol addition reaction with N-methyl alpha-aminoaldehydes, which relies on a camphor-derived chiral lithium acetate enolate reagent. The scope of this aldol reaction is investigated and its potential application to the synthesis of other structurally related, biologically relevant compounds illustrated. Remarkably, the chiral tether in the resulting gamma-amino aldol adducts sterically protect the carbonyl group, thus avoiding intramolecular cyclization during the amino group deprotection and the subsequent segment coupling event. After successful segment coupling and smooth, clean release of the chiral auxiliary, a new macrolactonization protocol, based on the principle of double activation of both reactive sites, is applied, which leads to the 12-membered macrolactone hapalosin in unprecedented chemical efficiency.

Depsipeptides↗
PubMed2004

2'-(4-Fluorophenyl)-[1,2,3]triazolo[4',5':16,17]androst-5-en-3beta-ol methanol hemisolvate.

The asymmetric unit of the title compound, C(25)H(30)FN(3)O.0.5CH(3)OH, contains four symmetry-independent steroid and two methanol molecules. The conformations of the independent steroid molecules are very similar. Intermolecular O-H.O hydrogen bonds create two independent chains, each of which links two of the independent steroid molecules plus one methanol molecule via a co-operative O-H.O-H.O-H pattern. Intermolecular C-H.O and C-H.F interactions are also observed.

Androstenols↗
PubMed2004

An aza-steroidal [17,16-c]pyrazole derivative: 2'-(p-fluorophenyl)-17a-aza-2'H-pyrazolo[4',3':16,17]-D-homoandrost-4-en-3-one.

The asymmetric unit of the title compound, C(26)H(30)FN(3)O, contains two crystallographically independent molecules, the core skeletons of which have the same absolute configuration and almost identical conformations, except for differences in the orientation of the p-fluorophenyl ring. The tetrahydropyridine ring adopts a half-chair conformation, while the cyclohexenone ring has a slightly distorted envelope conformation. The cyclohexane rings have chair conformations, sometimes slightly distorted. Intermolecular N-H.O, N-H.N and C-H.F interactions and an intramolecular C-H.N interaction are observed.

Journal Article↗
PubMed2004

16-(4-Isopropylbenzylidene)androst-4-ene-3,17-dione.

In the title compound, C(29)H(36)O(2), the outer cyclohexene ring of the steroid nucleus has a conformation that lies about half-way between a half-chair and an envelope, while the central and outer cyclohexane rings of the steroid nucleus have slightly distorted chair conformations. The steroidal cyclopentane ring adopts a 13beta,14alpha-half-chair conformation. The benzylidene moiety has an E configuration with respect to the carbonyl group on the cyclopentane ring. The dihedral angle between the mean planes of the steroid nucleus and the benzylidene moiety is 35.54 (9) degrees. The packing of the molecules is assumed to be dictated mainly by weak intermolecular C-H.O interactions.

Journal Article↗
PubMed2004

Solution-phase synthesis of Aib-containing cyclic hexapeptides.

The 18-membered Aib-containing cyclohexapeptides, cyclo(-Gly-Aib-Aib-Gly-Aib-Phe-) (22), cyclo(-Gly-Aib-Phe(2Me)-Gly-Aib-Aib-) (24a), cyclo(-Gly-Phe(2Me)-Aib-Gly-Aib-Aib-) (24b), and cyclo(-Gly-Phe(2Me)-Aib-Gly-Aib-Phe-) (25), have efficiently been synthesized by solution-phase techniques. The linear precursors 1a-1d were prepared by combining the 'azirine/oxazolone method' for incorporation of alpha,alpha-disubstituted alpha-amino acids (Aib, Phe(2Me)) into the peptide chains by classical peptide coupling methods for segment condensations. Deprotection of the amino and carboxy termini of 1a-1d, followed by cyclization with DEPC as the coupling reagent, gave the above-mentioned cyclic hexapeptides 22, 24a, 24b, and 25 in good yields (26-57%). The solid-state conformations of the linear hexapeptides 1d, 16 and 27, and of the cyclohexapeptides 22 and 25 have been established by X-ray crystallography.

Aminoisobutyric Acids↗
PubMed2004

Inhibiting activities of the secondary metabolites of Phlomis brunneogaleata against parasitic protozoa and plasmodial enoyl-ACP Reductase, a crucial enzyme in fatty acid biosynthesis.

Anti-plasmodial activity-guided fractionation of Phlomis brunneogaleata (Lamiaceae) led to the isolation of two new metabolites, the iridoid glycoside, brunneogaleatoside and a new pyrrolidinium derivative (2 S,4 R)-2-carboxy-4-( E)- p-coumaroyloxy-1,1-dimethylpyrrolidinium inner salt [(2 S,4 R)-1,1-dimethyl-4-( E)- p-coumaroyloxyproline inner salt]. Moreover, a known iridoid glycoside, ipolamiide, six known phenylethanoid glycosides, verbascoside, isoverbascoside, forsythoside B, echinacoside, glucopyranosyl-(1-->G (i)-6)-martynoside and integrifolioside B, two flavone glycosides, luteolin 7- O-beta- D-glucopyranoside ( 10) and chrysoeriol 7- O-beta- D-glucopyranoside ( 11), a lignan glycoside liriodendrin, an acetophenone glycoside 4-hydroxyacetophenone 4- O-(6'- O-beta- D-apiofuranosyl)-beta- D-glucopyranoside and three caffeic acid esters, chlorogenic acid, 3-O-caffeoylquinic acid methyl ester and 5- O-caffeoylshikimic acid were isolated. The structures of the pure compounds were elucidated by means of spectroscopic methods (UV, IR, MS, 1D and 2D NMR, [alpha] (D)) and X-ray crystallography. Compounds 10 and 11 were determined to be the major anti-malarial principles of the crude extract (IC (50) values of 2.4 and 5.9 micrograms/mL, respectively). They also exhibited significant leishmanicidal activity (IC (50) = 1.1 and 4.1 micrograms/mL, respectively). The inhibitory potential of the pure metabolites against plasmodial enoyl-ACP reductase (FabI), which is the key regulator of type II fatty acid synthases (FAS-II) in P. falciparum, was also assessed. Compound 10 showed promising FabI inhibiting effect (IC (50) = 10 micrograms/mL) and appears to be the first anti-malarial natural product targeting FabI of P. falciparum.

Animals↗
PubMed2004

Studies on 3-diethylaminocarbonyl-1,4,5,6,7,8-hexahydroquinoline derivatives and their calcium channel antagonistic activities in vitro.

In this study, thirteen 2,6,6-trimethyl-3-carbamoyl-4-aryl-5-oxo-1,4,5,6,7,8-hexahydroquinoline derivatives were synthesized and screened for their calcium channel antagonistic actitivities. The hexahydroquinoline derivatives were synthesized according to Hantzsch reaction. The structures of the compounds were elucidated by IR, 1H-NMR, 13C-NMR, Distortionless Enhancement Polarization Transfer (DEPT), Correlation Spectroscopy (COSY), mass spectroscopy and elemental analyses. The calcium antagonistic activities of the compounds were determined by tests performed on isolated rat ileum and lamb carotid artery. In isolated rat ileum, compounds 8, 12 and 13 were found to be more active than nicardipine (CAS 55985-32-5) at a concentration of 10(-5) mol/L. At the concentration 10(-4) mol/L, compounds 7 and 12 were more active than nicardipine and compounds 5, 8 and 13 were equipotent. In lamb carotid artery studies, at the concentration 10(-5) mol/L all compounds were found to be less active than nicardipine; at the concentration 10(-4) mol/L compounds 5 and 13 showed greater inhibition than nicardipine. At this concentration, compound 9 was found to be as active as nicardipine.

Animals↗
PubMed2003

Development of a new family of conformationally restricted peptides as potent nucleators of beta-turns. Design, synthesis, structure, and biological evaluation of a beta-lactam peptide analogue of melanostatin.

Novel enantiopure (i)-(beta-lactam)-(Gly)-(i+3) peptide models, defined by the presence of a central alpha-alkyl-alpha-amino-beta-lactam ring placed as the (i+1) residue, have been synthesized in a totally stereocontrolled way by alpha-alkylation of suitable N-[bis(trimethylsilyl)methyl]-beta-lactams. The structural properties of these beta-lactam pseudopeptides have been studied by X-ray crystallography, Molecular Dynamics simulation, and NOESY-restrained NMR simulated annealing techniques, showing a strong tendency to form stable type II or type II' beta-turns either in the solid state or in highly coordinating DMSO solutions. Tetrapeptide models containing syn- or anti-alpha,beta-dialkyl-alpha-amino-beta-lactam rings have also been synthesized and their conformations analyzed, revealing that alpha-alkyl substitution is essential for beta-turn stabilization. A beta-lactam analogue of melanostatin (PLG amide) has also been prepared, characterized as a type-II beta-turn in DMSO-d6 solution, and tested by competitive binding assay as a dopaminergic D2 modulator in rat neuron cultured cells, displaying moderate agonist activity in the micromolar concentration range. On the basis of these results, a novel peptidomimetic design concept, based on the separation of constraint and recognition elements, is proposed.

Animals↗
PubMed2003

Two androst-5-ene derivatives: 16-[4-(3-chloropropoxy)-3-methoxybenzylidene]-17-oxoandrost-5-en-3 beta-ol and 16-[3-methoxy-4-(2-pyrrolidin-1-ylethoxy)benzylidene]-3 beta-pyrrolidinoandrost-5-en-17 beta-ol monohydrate.

In the steroidal nucleus of 16-[4-(3-chloropropoxy)-3-methoxybenzylidene]-17-oxoandrost-5-en-3 beta-ol, C(30)H(29)ClO(4), (I), the outer two six-membered rings are in chair conformations, while the five-membered ring and the central six-membered ring of the steroidal nucleus adopt half-chair and envelope conformations, respectively. In 16-[3-methoxy-4-(2-pyrrolidin-1-ylethoxy)benzylidene]-3 beta-pyrrolidinoandrost-5-en-17 beta-ol monohydrate, C(37)H(54)N(2)O(3).H(2)O, (II), one C atom of one of the outer six-membered rings of the steroid nucleus and the four C atoms of the ethoxypyrrolidine ring are disordered over two sites. The five-membered ring, and the central and one of the outer six-membered rings of the steroidal nucleus exhibit distorted half-chair, chair and envelope conformations, respectively. In (I), intermolecular O-H...O hydrogen bonds link the molecules into chains via a co-operative O-H...O-H...O-H pattern. In (II), intermolecular O-H...O and O-H...N hydrogen bonds link the steroid and water molecules alternately into extended chains.

Androstenes↗
PubMed2003

Two azasteroidal [3,2-c]pyrazole derivatives: 2'-(p-fluorophenyl)-4-azapyrazolo[4',3':2,3]-5alpha-androstan-17beta-yl acetate and 2'-(p-fluorophenyl)-4-azapyrazolo[4',3':2,3]-5alpha-androstan-17beta-ol.

In both the title aza-steroids, 2'-(p-fluorophenyl)-4-azapyrazolo[4',3':2,3]-5alpha-androstan-17beta-yl acetate, C(27)H(34)FN(3)O(2), (I), and 2'-(p-fluorophenyl)-4-azapyrazolo[4',3':2,3]-5alpha-androstan-17beta-ol, C(25)H(32)FN(3)O, (II), the tetrahydropyridine ring adopts a half-chair conformation and is considerably strained as a consequence of the presence of the fused planar pyrazole ring. In both compounds, both cyclohexane rings have chair conformations, while the cyclopentane ring has an envelope conformation. All the rings of the steroid nucleus are trans fused. In (I), intermolecular N-H.O, C-H.F, C-H.O and C-H.N interactions are observed in the solid state, while intermolecular N-H.O and O-H.N hydrogen bonds are observed in (II).

Acetates↗