Darin E. Jones

Intramolecular 4+3 cycloadditions. Vinylthionium ions from allylic alcohols

Abstract Aldehyde 9 can be prepared from ethyl pyruvate in several steps. Treatment of 1 with various diene-containing Grignard reagents results in the formation of the corresponding allylic alcohol in good yield. Exposure of these alcohols to triflic anhydride results in the formation of 4+3 cycloadducts in good to excellent yields. Furan and simple butadiene trap the intermediate allylic cation efficiently in the formation of 5,7-fused ring systems. A tethered thiophene undergoes only intramolecular Friedal-Crafts alkylation.

The metallation of Troeger's base

Abstract Complexation of Troegers base with boron trifluoride etherate followed by treatment with n-BuLi results in the formation of an anion. This reacts with electrophiles stereoselectively to give alkylation products in good to excellent yields.

Chiral cations in 4+3 cycloadditions

Abstract The reaction of the chiral acetal 4 with furan and cyclopentadiene in the presence of a Lewis acid gives 4+3 cycloadducts in very good yields. Diastereoselectivity in the case of furan is exceptionally high, while that for the reaction with cyclopentadiene is lower. The sense of diastereoselection in the case of furan is opposite to that which would be predicted on the basis of mechanistic models for the origin of stereoselectivity in many reactions of chiral acetals mediated by Lewis acids.

The reaction of N-phenylsulfonimidoyl chloride with trimethylsilylethene. A new route to 2-alkenylanilines

N-Phenylsulfonimidoyl chloride reacts with trimethylsilylethene in the presence of aluminum chloride to give two product benzothiazines, one of which has been desilylated. The silylated benzothiazine can be deprotonated and alkylated, sometimes with very high diastereocontrol. Upon treatment with fluoride, these silylated benzothiazines undergo desilylation with concomitant cleavage of the carbon-sulfur bond to give 2-alkenylsulfinanilides which can be hydrolyzed to the corresponding anilines.

Cloning, sequence, and expression of a blood group B active recombinant α‐D‐galactosidase from pinto bean (Phaseolus vulgaris)

A cDNA encoding pinto bean α‐D‐galactosidase [E.C. 3.2.1.22] was obtained by amplification of cDNA using highly conserved sequences found in eucaryotic α‐D‐galactosidases. Subsequently a full length Phaseolus cDNA clone was obtained that is 1537 nt long and contains untranslated 5′ and 3′ sequences. The nucleotide sequence of the cDNA has a high degree of homology with other eucaryotic (α‐D‐galactosidase genes. The recombinant α‐D‐galactosidase (rGal) was expressed in Escherichia coli and purified by ion exchange and affinity chromatography. Purified rGal was homogeneous by SDS‐PAGE and had relative masses of 40.1 and 45.4 kDa under nonreducing and reducing conditions, respectively. The N‐terminal sequence of the expressed protein contained the sequence GNGLGQTPPMG corresponding to that deduced from the cDNA sequence. The native molecular weight for rGal was determined to be 32.18 kDa by Sephacryl S‐200 chromatography. The specific activity of the rGal was 349 μmoles of PNP‐α‐D‐galactopyranoside hydrolyzed per mg of pure rGal per min. rGal was highly specific for α‐D‐galactosyl residues and degraded B oligosaccharide. No detectable hemagglutinin or protease activity was present in the preparations. Furthermore, rGal was active against the blood group B antigen on native human erythrocytes in cell suspension assays. The only detectable RBC phenotypic change was loss of the B and P1 epitopes. Recombinant Phaseolus vulgaris α‐D‐galactosidase may have useful biotechnical applications in the potential mass production of enzymatically converted, universally transfusable type O RBCs.

A GENERAL, REGIOSELECTIVE APPROACH TO THE SYNTHESIS OF ORTHO ALLYLANILINES

Abstract Readily available 2,1-benzothiazines can be alkylated via deprotonation with butyllithium followed by treatment with iodomethyltrimethylsilane. Subsequent treatment with fluoride and hydrolysis leads to ortho allyl anilines in high yield. The reaction is general and regioselective by virtue of these characteristics being present in the Lewis acid mediated reaction of alkenes and sulfonimidoyl chlorides, the reaction which leads to the 2,1-benzothiazines used as starting materials.

Heteroatom-stabilized allylic cations in 4+3 cycloadditions. A tandem Peterson olefination/4+3 cycloaddition reaction

The readily available tertiary alcohols 4a-c react with selected dienes in the presence of titanium tetrachloride to give 4+3 cycloaddition products. The process is best rationalized as a Peterson olefination followed by allylic cation formation and 4+3 cycloaddition.

Structure-activity relationships among DNA ligase inhibitors: Characterization of a selective uncompetitive DNA ligase I inhibitor

In human cells, there are three genes that encode DNA ligase polypeptides with distinct but overlapping functions. Previously small molecule inhibitors of human DNA ligases were identified using a structure-based approach. Three of these inhibitors, L82, a DNA ligase I (LigI)-selective inhibitor, and L67, an inhibitor of LigI and DNA ligases III (LigIII), and L189, an inhibitor of all three human DNA ligases, have related structures that are composed of two 6-member aromatic rings separated by different linkers. Here we have performed a structure-activity analysis to identify determinants of activity and selectivity. The majority of the LigI-selective inhibitors had a pyridazine ring whereas the LigI/III- and LigIII-selective inhibitors did not. In addition, the aromatic rings in LigI-selective inhibitors had either arylhydrazone or acylhydrazone, but not vinyl linkers. Among the LigI-selective inhibitors, L82-G17 exhibited increased activity against and selectivity for LigI compared with L82. Notably. L82-G17 is an uncompetitive inhibitor of the third step of the ligation reaction, phosphodiester bond formation. Cells expressing LigI were more sensitive to L82-G17 than isogenic LIG1 null cells. Furthermore, cells lacking nuclear LigIIIα, which can substitute for LigI in DNA replication, were also more sensitive to L82-G17 than isogenic parental cells. Together, our results demonstrate that L82-G17 is a LigI-selective inhibitor with utility as a probe of the catalytic activity and cellular functions of LigI and provide a framework for the future design of DNA ligase inhibitors.