Richard G. Lawton

Titanium Chelation in Regioselective Michael Additions to Conjugated Dienones and Trienones.

Abstract The site of Michael addition of β-hetero atom substituted thiols (such as mercaptoethanol) to unsubstituted 2, 4-dienone and 2, 4, 6-trienones is at the terminal (ω) position. This site preference is transferred to the β site when the addition is accomplished using Ti +4 complexation. These β site addition products rapidly rearrange to the ω position on base treatment.

Coupling an α2-Adrenergic receptor peptide to G-protein: A new photolabeling agent

Abstract A photoreactive derivative of a tetradecapeptide G-protein activator (peptide Q) derived from the α 2 - adrenergic receptor was designed and used to label purified G-protein (Go/Gi). N- bromoacetyl -N′-(3- diazopyruvoyl )-m- phenylene-diamine (Br-DAP) was conjugated to the C- terminal cysteine of peptide Q. The DAP-modified peptide Q (DAP-Q) specifically incorporated into the a subunit of Go. The incorporation of DAP-Q into α o was blocked by unmodified Q peptide ( IC 50 = 15 ± 6 μM ; n = 4 ). Photolysis of sixfold higher concentrations of DAP-Q with ovalbumin or bovine albumin failed to produce cross-linked products. Br-DAP should prove useful in detecting mutual contact sites between peptides and their binding proteins.

An efficient synthetic route to 2-(1,2-dithiolan-3-yl)acetic acid. Trisnorlipoic acid and amide derivatives

Abstract A simple, efficient synthesis of 2-(1,2-dithiolan-3-yl)acetic acid from Meldrums acid, acrolein and thioacetic acid is described. The isopropyldene 2,4- bis (acetylthio)butane-1,1-dicarboxylate formed in the three-component, single container process, can be methanolized to the corresponding dimethyl ester and then hydrolyzed, oxidized to the disulfide and decarboxylated to 2-(1,2-dithiolan-3-yl)acetic acid. The acid can be converted by conventional reagents into a variety of amide derivatives.

Streptavidin-biotinylated IgG conjugates: a simple procedure for reducing polymer formation

Disulfide links of the IgG2ak anti-ovarian carcinoma antibody, 5G6.4, were site-specifically biotinylated [approximately 2 biotins/IgG2a] using a novel crosslinking procedure using the biotin derivatized ETAC (equilibrium transfer alkylation crosslink reagent) 1a. Complexation of ETAC 1a biotinylated 5G6.4 on a column of immobilized protein A at high dilution, followed by passage of [125I]streptavidin, washing and pH change leads to elution of a streptavidin-free product with a molecular mass in the 200-300 kDa range. By contrast, direct mixing with [125I]streptavidin rapidly gave larger oligomers of much greater than 669 and approximately 440-669 kDa molecular mass, respectively. The biodistribution of the 200-300 kDa complex showed significantly diminished liver, kidney and spleen uptake as well as higher blood activity than the 440-669 kDa complex. The methodology represent the first application of ETAC chemistry to disulfide-bond directed biotinylation of antibodies and the synthesis of streptavidin antibody conjugates which minimizes their polymerization.

Intramolecular photochemical closure to 4-tryptophan-substituted tiglate derivatives

in vivo condensation of the dimethylallyl moiety to the 4-position of the tryp-tophan indole is strongly guided by spatial and structural constraints. 1 Continuing our studies on the interaction of functional groups along peptide chains, 2 we searched for a molecule in which intramolecular alkylation by the dimethylallyl side chain at the appropriate indole position would be spatially favored. y-Chlorotiglyl L-tryptophan methyl ester, I, seemed a good choice. Examination of a Bfichi model of 1 in its cis amide form showed that the methylene of the tiglyl side chain may be placed directly above the C-4 of the indole, and is closer to this carbon than to any other atom of the indole

AROMATIC STACKING IN FOLDED ARCHITECTURES THROUGH HYDROGEN BONDING

Abstract The α, α′-annelation of the enamine of 1,3-dihydro-2-phenalenone with methyl α-(bromomethyl)acrylate affords an aromatic bicyclic framework, methyl 8,9,10,11-tetrahydro-7,11-methano-12-keto-7H-cyclooocta(de)naphthalene-9-endo-carboxylate having the ester function positioned over the aromatic ring. The acid derivatives of this framework dimerize affording a “sandwich” structure with the H-bonded carboxyl groups between parallel naphthalene rings. The dimeric association can be easily probed using both NMR and fluorescence techniques.

Intramolecular carboxylate capture of an intermediate in aromatic electrophilic substitution. The 8,9,10,11-tetrahydro-7.11-methano-7H-cycloocta[de]naphthalene-9-endo-carboxylic acid system

Abstract The α, α′-annelation of the enamine of 1,3-dihydro-2-phenalenone with methyl α-(bromomethyl)acrylate affords an aromatic bicyclic framework, methyl 8,9,10,11-tetrahydro-7,11-methano-12-keto-7H-cycloocta( de )-naphthalene-9- endo -carboxylate having the ester function positioned over the aromatic ring. The 9- exo -methyl-12, 12-dimethoxy ketal carboxylate anion derivative reacts with excess Br 2 in aqueous solution affording the bromo lactone epoxide derived through capture of the intermediate of electorphilic attack on the naphthalene ring, 12, 12-dimethoxy-2, 3- endo -epoxy-11a- endo -hydroxy-1- exo , 4-dibromo-7, 11-methano-9-methyl-11a, 1, 2, 3, 4, 8, 9, 10, 11-octahydro-7 H-cycloocta [ de ] naphthalene-9- endo -carboxylic acid δ lactone.

Thioalkylation of Meldrum's Acid with Dialdehydes. Isopropylidene cis-2-Hydroxy-6-phenylthiocyclohexane-1,1-dicarboxylate Derivatives

Abstract Reaction of Meldrums acid, thiophenol and gluteraldehyde in aqueous acetonitrile with piperidine acetate affords a 70% yield of isopropylidene cis -2-hydroxy-6-phenylthiocyclohexane-1,1-dicarboxylate. The reaction is very general. It can be applied to dialdehydes derived in a many ways using many different thiols.

Heterobifunctional cross-linking of a monoclonal antibody with 2-methyl-N1-benzenesulfonyl-N4-bromoacetylquinonediimide

The Cyssor reagent, 2-methyl-N1-benzenesulfonyl-N4-bromoacetylquinonediimide, which will cleave a protein chain at Cys under acidic conditions, cross-linked unreduced and partially reduced antibody at pH 8.0. No cleavage of the antibody occurred suggesting that the Cyssor reagent may be useful with certain proteins as a heterobifunctional cross-linker.

Intramolecular photoinduced electron transfer: A dimethylaniline constrained to the face of a naphthalene through a bicyclic scaffold

Abstract The α, α′-annelation of the enamine of 1,3-dihydro-2-phenalenone with ETAC-I [2-(p-nitrophenyl)allyl trimethylammonium iodide] affords an aromatic bicyclic framework, 9-endo-p-nitrophenyl-8,9,10,11-tetrahydro-7,11-methano-12-keto-7H-cyclooocta(de)naphthalene having the p-nitrophenyl group positioned over the naphthalene ring. The X-ray structure of a derivative was obtained. The nitro function was transformed to a dimethylamino group giving a molecule well suited to evaluate intramolecular photoinduced electron transfer [PET] between the two aromatic elements. The charge transfer [CT] was determined using solvents of different polarity in the examination of the fluorescence spectra.