Biomedical subjects

Anthony Linden

Publications and source records attributed to Anthony Linden.

61 records · Page 4Linked to original sources

PubMed2002

The dimer, trimer and 1,2,4-trithiolane of adamantanethione.

The molecules of dispiro[1,3-dithietane-2,2':4,2"-diadamantane], C(20)H(28)S(2), have crystallographic C(i) symmetry, as well as local D(2h) symmetry, and a planar 1,3-dithietane ring. The molecules of trispiro[1,3,5-trithiane-2,2':4,2":6,2"'-triadamantane], C(30)H(42)S(3), have approximate C(2) symmetry and the 1,3,5-trithiane ring has a twist-boat conformation. The C-S-C bond angles within the ring are about 8 degrees larger than observed in most related 1,3,5-trithiane structures. In dispiro[1,2,4-trithiolane-3,2':5,2"-diadamantane], C(20)H(28)S(3), the molecules have local C(2) symmetry and the 1,2,4-trithiolane ring has a half-chair conformation.

Journal Article↗

PubMed2002

2-(4-Chlorophenyl)-1,3-dicyano-6,7-dihydro-4-imino-9,10-dimethoxybenzo[a]quinolizine-water (2/5).

Crystals of the title compound, C(23)H(17)ClN(4)O(2).2.5H(2)O, contain channels filled with highly disordered water molecules. The best structure refinement was obtained by removing the solvent contribution from the intensity data and refining against a solvent-free model. The central six-membered ring of the quinolizine molecule has a slightly distorted screw-boat conformation.

Agrochemicals↗

PubMed2001

A second polymorph of 1,1,4,4-tetramethylpiperazinium pentabromothallate(III).

A new polymorph of the title compound, (C8H20N2)[TlBr5], contains cations located about crystallographic centres of inversion and trigonal-bipyramidal anions which have a C2 axis passing through the equatorial plane of the anion. The anion has the least distorted geometry seen so far in any structure possessing this anion and the axial Tl-Br bonds are about 0.13 A longer than the equatorial Tl-Br bonds, consistent with related structures. The anion in the initially reported polymorph has lower symmetry and a greater distortion of the trigonal-bipyramidal coordination.

Journal Article↗

PubMed1999

Highly Diastereoselective Aldol Reactions with Camphor-Based Acetate Enolate Equivalents.

New lithium enolates of alpha-hydroxy ketones, derived from camphor, are evaluated for asymmetric aldol reactions in the presence of lithium chloride. The diastereoselectivity of the reactions between the lithium enolate of 3 and a variety of achiral aldehydes is strongly influenced by the lithium chloride salt. In these instances, the achieved levels of asymmetric induction, typically 95:5 dr, are in the range of those attained in aldol reactions involving the lithium enolate of the methyl ketone 4, which is sterically more demanding. The resulting aldol adducts are easily transformed into beta-hydroxy carboxylic acids, ketones, and aldehydes with concomitant recovery of the camphor, the chiral controller of the process, which can be reused.

Journal Article↗

PubMed1998

Practical Synthesis of alpha-Amino Acid N-Carboxy Anhydrides of Polyhydroxylated alpha-Amino Acids from beta-Lactam Frameworks. Model Studies toward the Synthesis of Directly Linked Peptidyl Nucleoside Antibiotics.

A straightforward method for the synthesis of polyhydroxylated alpha-amino acid N-carboxy anhydrides (NCAs) is described as the means by which short peptide segments comprised of a polyhydroxylated chain are easily affordable. The entire sequence lies in the preparation of nonracemic 3-hydroxy beta-lactams through the highly diastereoselective Staudinger reaction of hydroxyketene equivalents with chiral alpha-oxyaldehyde-derived imines, followed by TEMPO radical assisted cycloexpansion to the corresponding NCA and subsequent peptide coupling with alpha-amino acid esters. The method has been applied to the synthesis of short peptide segments derived from carbamoylpolyoxamic acid, some glycoglycines, as well as C(2) symmetric hydroxy amino acids.

Journal Article↗

PubMed1997

Construction of Quaternary Stereogenic Centers via [2 + 2] Cycloaddition Reactions. Synthesis of Homochiral 4,4-Disubstituted 2-Azetidinones and Imine Substituent Effects on beta-Lactam Formation.

A study on the asymmetric construction of quaternary stereogenic centers via [2 + 2] cycloaddition reaction of ketenes with ketimines is described. Reaction of achiral ketenes and chiral alpha-alkoxy ketone-derived imines resulted in formation of new beta-lactams as single diastereomers. The cycloaddition was extended to pyruvate imines, aralkyl ketone-derived imines, and dialkyl ketimines. In these cases the asymmetric induction was satisfactorily achieved using beta-silylalkanoyl ketenes and the Evans-Sjögren ketene. C,C-Bis (trimethylsilyl)methylamine ketimines derived from enolizable dialkyl ketones cleanly led to the corresponding C(4) disubstituted beta-lactams without deprotonation. Therefore, a general methodology for a convergent asymmetric synthesis of beta-lactams in which C(4) exists as a quaternary carbon is provided.

Journal Article↗

PubMed1996

Generation of Threonine- and Azathreonine N-Carboxy Anhydrides from alpha-Hydroxy beta-Lactams Promoted by 2,2,6,6-Tetramethylpiperidinyl-1-oxyl (TEMPO) in Combination with Sodium Hypochlorite.

A versatile one-pot oxidation-Baeyer-Villiger reaction sequence applied to alpha-hydroxy beta-lactams and promoted by 2,2,6,6-tetramethylpiperidinyl-1-oxyl (TEMPO) leads to alpha-amino acid N-carboxy anhydrides. The examples reported constitute the first application of TEMPO in a Baeyer-Villiger reaction and provide a way for peptide coupling from non alpha-amino acid precursors.

Journal Article↗