Intramolecular 4 + 3 cycloadditions. A theoretical analysis of simple diastereoselectivity in reactions of alkoxyallylic cations and furans

[reaction--see text] A computational examination (B3LYP/6-31+G*//HF/6-31+G* + ZPVE) of an intramolecular 4 + 3 cycloaddition reaction suggests a stepwise process and the likelihood of reversibility in at least one of the pathways examined.

A new, chiral bis-benzothiazine ligand

[reaction: see text]. The synthesis and application of a new, chiral bis-benzothiazine ligand are described.

A 4 + 3 cycloaddition approach to the synthesis of spatol. A formal total synthesis of racemic spatol

[reaction: see text] A formal total synthesis of racemic spatol is presented. The key steps involved a 4 + 3 cycloaddition of a halogenated cyclopentenyl cation to cyclopentadiene and a quasi-Favorskii rearrangement.

Exploration of fundamental and synthetic aspects of the intramolecular 4 + 3 cycloaddition reaction

In this Account, a summary of our work in the exploration and development of intramolecular 4 + 3 cycloaddition reactions between dienes and allylic cations is presented. Alkoxyallylic sulfones are useful precursors for the generation of allylic cations which are good dienophiles. Such substrates allowed a number of important pieces of data concerning the cycloaddition to be obtained. The evolution of the work has involved pursuing other methods for allylic cation generation, an investigation of stereochemical variables and applications, including the total syntheses of aphanamol I, widdrol, and (+)-dactylol.

Intramolecular 4 + 3 cycloadditions. Aspects of stereocontrol in the synthesis of cyclooctanoids. A synthesis of (+)-dactylol

[reaction: see text] The judicious placement of stereocenters on precursors for 4 + 3 cycloaddition reactions can lead to high levels of stereocontrol in the 4 + 3 cycloaddition process of cyclopentenyl cations and tethered butadienes. This concept was successfully tested in the context of a synthesis of (+)-dactylol.

A One-Pot, One-Operation

Enantiomerically pure 2,1-benzothiazines are readily prepared by a one-pot, one-operation procedure consisting of a palladium-catalyzed aryl amination of an ortho-bromobenzaldehyde with a sulfoximine followed by an intramolecular condensation reaction [Eq. (1)]. BINAP=1,1'-binaphthalene-2,2'-diylbis(diphenylphosphane).

Characterization of Gallus domesticus alpha-N-acetyl-galactosaminidase blood group A2 activity

Soluble A antigens and an enzyme-linked immunosorbent assay (ELISA) using type A2 erythrocyte membranes were used to study the activity of an alpha-N-acetyl-galactosaminidase from Gallus domesticus (domestic chicken). The enzyme readily hydrolyzed the terminal N-acetyl-alpha-D-galactosamine of the A antigen under a variety of conditions, converting it to H antigen. Conversion of the A antigen to H antigen produces blood type O, which is universally transfusable. These preliminary studies are important in determining optimal conditions for enzymatic conversion of blood type A to O if efficient large scale production of enzymatically converted, universally transfusable red blood cells is to be achieved.

Purification and characterization of N-acetyl-alpha-D-galactosaminidase from Gallus domesticus

Exoglycosidases modify carbohydrate epitopes on glycoproteins and glycolipids. The N-acetyl-alpha-D-galactosaminidase from the domestic chicken, Gallus domesticus, is an important exoglycosidase which degrades the human blood group A epitope. This enzyme has never been demonstrably purified or thoroughly characterized. We have developed a technique to purify this enzyme to homogeneity. The isolated enzyme has a molecular weight of 49.1 kDa by SDS PAGE and 145.0 kDa by gel filtration. The enzyme is highly selective for PNP-N-acetyl-alpha-D-galactosaminide and is inactive against other low molecular weight substrates. The enzyme hydrolyzes the terminal N-acetyl-alpha-D-galactosaminide residues from blood group A2 erythrocytes. Protease activity is below detectable limits. The enzyme has a pH optima of 3.7, a pI of 8.15, is relatively unaffected by ionic strength, and is stable at 4 degrees C.

Purification and characterization of a Coffea canephora alpha-D-galactosidase isozyme

Exoglycosidases modify carbohydrate epitopes on glycoproteins and glycolipids. The alpha-D-galactosidase from Coffea canephora is an important exoglycosidase which degrades the human blood group B epitope. Although multiple isozymes have been described, they have never been demonstrably purified and thoroughly characterized. We have developed a technique to purify an isozyme to homogeneity. The isolated enzyme has a molecular weight of 36.7 kDa by SDS PAGE and 34.0 kDa by gel filtration. The isozyme is highly selective for alpha-D-galactosides and inactive against other low molecular weight substrates. It hydrolyzes the the terminal alpha-D-galactosyl residue from the blood group B epitope. Protease activity is below detectable limits. The isozyme has a broad pH optima at 6.3, a pl of 7.03, is unaffected by ionic strength, and is stable at 4 degrees C.