Anna Compagnini

Isolation by gel-permeation chromatography of a non-covalent complex of Cibacron Blue F3G-A with human serum albumin.

The isolation by gel-permeation chromatography on Sephadex G-100 of a non-covalent complex of Cibacron Blue F3G-A (CB) with human serum albumin (HSA) is described. The complex presents a molar ratio of 3:1 CB-HSA and can be re-chromatographed under the same conditions without modification of its composition. However, complete dissociation occurs when the complex is chromatographed in the presence of denaturing agents. The effect of pH on the molar composition of the complex was also investigated by gel-permeation chromatography. Analogous complexes between CB and A and C cyanogen bromide fragments of unreduced HSA were also isolated by gel-permeation chromatography on Sephadex G-50. They present a molar ratio of 0.8:1 and 1.3:1 CB-protein for fragments A and C, respectively. These results suggest that two of the three molecules of CB bound to HSA may be located in the hydrophobic pocket corresponding to subdomain IIA, with the other molecule in the hydrophobic site corresponding to subdomain IIIA. The UV-Vis and dichroic circular spectra of the isolated complexes are reported.

A New Labile Bromoterpenoid from the Red Alga Laurencia Majuscula: Dehydrochloroprepacifenol

Abstract A new labile brominated chamigrene, dehydrochloroprepacifenol, was isolated from the red alga Laurencia majucula. The structure of this compound was determined by its spectral properties and low-temperature X-ray diffraction analysis.

Chromatographic profiles of cyanogen bromide fragments of unreduced human serum albumin on immobilized Cibacron Blue F3G-A

Abstract The elution profiles of cyanogen bromide fragments A (299–585), B (1–123), C (124–298) and D (1–298) of unreduced human serum albumin (HSA) on Cibacron Blue F3G-A immobilized on Sepharose CL-6B are reported. The binding properties of fragments C and D are similar to those of HSA, whereas fragment A shows a slightly lower retention time. Fragment B, in contrast, does not interact with the dye. The different chromatographic behaviour of fragments B and C allows their fast separation by combined use of gel permeation and dye-protein affinity chromatography.

The triethylamine catalyzed reaction of N,N-disubstituted thioamide–bromine adducts with unsubstituted thiobenzamide

The reaction of N,N-disubstituted thioamide–bromine adducts with unsubstituted thioamide, followed by treatment with triethylamine, affords novel N′-thiobenzoylamidines along with smaller amounts of secondary products. A mechanism is proposed for the formation of the amidines. The results give an insight into the initial steps of the mechanism by which thioamides are converted into 1,2,4-thiadiazoles.

An Improved Synthesis of Substituted Thiazoles from Tricoordinate Dibromine Sulfuranes

Abstract Recently we reported the 1,5-electrocyclic closure of iminothiocarbonyl ylides (1) which provides high yields of 2,4-diaryl-5-cyanothiazoles (2). Transient ylides (1) were generated by triethylamine catalized deprotonation of sulfonium salts (3), these latter being obtained by sulfur ligand displacement reaction with enaminonitriles (4) of initially formed sulfonium salts upon interaction of N,N-disubstituted benzothio-amides and α-bromo-cyanoethtylacetate1.

The reaction of para-substituted β-aminocinnamonitriles with benzonitrile oxides

β-Aminocinnamonitrile para-substituted by electron-withdrawing groups (5a,b) with benzonitrile oxides (2) give the expected cycloadducts (6) to the C–N triple bond. The p-methyl derivative (5c) behaves similarly, but the yields are smaller. Reactions of (2) with derivatives para-substituted by electron-donating groups (5d,e) give two bis-adducts, the structures of which have been elucidated.

Improved accuracy in the matrix-assisted laser desorption/ionization-mass spectrometry determination of the molecular mass of cyanogen bromide fragments of proteins by post-cleavage reaction with tris(hydroxymethyl)aminomethane.

In order to improve the accuracy in the matrix‐assisted laser desorption/ionization mass spectrometry (MALDI‐MS) determination of the molecular mass of cyanogen bromide (CNBr) fragments of proteins, the post‐cleavage reaction of these fragments with tris(hydroxymethyl)aminomethane (Tris) was tested. Mixtures of homoserine and homoserine lactone peptide fragments originating from CNBr cleavage of cytochrome c, lysozyme and human serum albumin were used as model compounds. Reaction of these fragments with Tris converts quantitatively the homoserine lactone ending peptides into the corresponding amides, leaving unmodified the homoserine ending forms. Thus, pairs of fragments which differ by 103 Da are formed. In contrast to the unmodified CNBr mixtures of peptides, which, due to the overlap of the signals of the free homoserine and homoserine lactone forms, produce unresolved peaks in the high mass region of the MALDI spectra, these pairs of fragments give resolved doublets of peaks up to a mass of 20 000 Da. This permits accurate determination of the molecular mass of the fragments. Using this procedure, differences less than 5 Da with respect to the calculated values were obtained for the fragments examined.

Thermal and photochemical behaviour of N-(α-morpholinobenzyl)-benzamide and N-(α-methoxybenzyl) benzamide

The thermal fragmentation of the title compounds produces benzamide (6), benzaldehyde (7), and N,N′-benzylidenebisbenzamide (8); in contrast the photochemical reaction gives benzylbenzamide (9) and meso- and (±)-1-modifications of N,N′-dibenzoyl-1,2-diphenyl-1,2-diaminoethane (10). Evidence is presented which shows that the formation of the various reaction products starts from the N-benzylidenebenzamide (5).

Photorearrangement studies of 3-heteroaryl-substituted cyclopropenes

The photochemical rearrangement of several 3-heteroaryl-substituted cyclopropenes containing a methyl group on the heterocyclic ring has been studied. The rearrangements are derived from the π-π* singlet state of the cyclopropene. Ring-opening occurs to give a vinylcarbene intermediate which undergoes a subsequent electrocyclization. The resulting product was found to undergo a sigmatropic 1,5-methyl shift on being heated in mesitylene at 200 °C to give a cyclopenta[b]furan or thiophene. Yet another reaction resulting from the vinylcarbene is insertion into the adjacent methyl group to give a buta-1,3-diene derivative. The product distribution is dependent on the stereochemistry of the vinylcarbene. Irradiation of 1,2-diphenyl-3-heteroaryl-substituted cyclopropenes also give products corresponding to a 1,2-heteroaryl substituent shift. A mechanism involving π-π* bridging of the excited cyclopropene with the heteroaromatic ring followed by diradical cleavage is proposed to account for the formation of the rearranged cyclopropenes.

Photochemistry of cyclopropene derivatives. Ring-opening reaction of 3-heteroaryl substituted cyclopropenes

The photochemical rearrangement of several 3-heteroaryl substituted cyclopropenes has been studied. The rearrangements are derived from the π–π* singlet state of the cyclopropene. Ring opening occurs to give a vinylcarbene intermediate which undergoes a subsequent electrocyclization. The transient intermediate so produced can undergo either a 1,3- or a 1,5-sigmatropic hydrogen shift to give the observed products. One strong piece of evidence for carbene intervention is the observation of a 1,3-butadiene derivative as one of the photoproducts obtained from the photolysis of a 3-pyrrolyl substituted cyclopropene. The 1,3-diene is thought to be derived by insertion of the vinylcarbene into the neighbouring methyl group. The regioselectivity of the rearrangement can be accounted for in terms of competitive 1,3-and 1,5-sigmatropic hydrogen migrations.