James P. Springer

Reactions of cobalt carbene complexes with alkynes. .eta.4-Vinylketene-complexed intermediates and a novel synthesis of bovolide.

The combination of resonance Raman and isotopic work thus demonstrates conclusively that, for Rh2(02CCH3)4(PPh3)2, v(RhRh) is a t 289.3 cm-I. Since the RhRh bond length in this complex is 2.4505 (2) A, longer than in the analogous AsPh3 (2.427 (1) A),2 SbPh, (2.421 (4) A),* and H20 (2.3855 (5) A)I6 complexes, the implication is that v(RhRh) in these complexes must all lie above 289.3 cm-I, as indeed is found to be the case for the AsPh3 and SbPh, derivatives (vide supra). The high value for v(RhRh) is thought to arise from the significant contribution to the RhRh restoring force brought about by the four chelating acetate groups (primarily via the four OCO bending coordinates, which are coupled only in second order to the RhRh stretching coordinate). Full details of these and related studies will be published elsewhere.

Neolignans from PIPER futokadsura

Abstract The structures of three new neolignans, kadsurenone, kadsurin A and kadsurin B, isolated from Piper futokadsura were determined by chemical and spectral analysis and X-ray diffraction study. Their biological activities are reported.

Crystallization and X-ray analysis of stemphyloxin I, a phytotoxin from Stemphylium botryosum

Certain isolates of the plant-pathogenic fungus Stemphylium botryosum produce a phytotoxin, stemphyloxin I. This toxin (C21H34O6) was crystallized and its structure was determined by x-ray crystallography to be a β-ketoaldehyde trans-Decalin. This compound is a highly unusual natural product. Iron (Fe3+) controls production of toxin by this fungus. Furthermore, iron reacts with the toxin to yield a colored product which aids in its detection on chromatograms and in its quantitative estimation by colorimetry.;

Azapeptides: A new class of angiotensin-converting enzyme inhibitors

A class of potent inhibitors of angiotensin-converting enzyme (dipeptidyl carboxypeptidase, E.C. 3.4.15.1) is reported, in which an alpha-aza substitution into the substituted N-carboxymethyl dipeptide structure of enalapril is made. The inhibitors 2 exhibit striking alterations in their conformational and acid-base properties due to the aza substitution, as is clear from pKa data and the x-ray crystal structure of a model azapeptide. In spite of this, they bind tightly to the enzyme, with inhibitor potency comparable to that of captopril.

Isolation and identification of two new biologically active norditerpene dilactones from Aspergillus wentii

Abstract Two new biologically-active norditerpenoid dilactones were purified from culture extracts of Aspergillus wentii and assigned the trivial names wentilactone A and wentilactone B. The absolute chemical structure of wentilactone A was determined by single crystal X-ray diffraction and circular dichroism. The structure of wentilactone B was determined by 1 H and 13 C NMR analyses. Wentilactone A had an ld 50 of 7.0 mg/kg when administered orally to 1-day-old chickens. Both metabolites inhibited growth in wheat coleoptile bioassays.

Inhibition of procine kidney “enkephalinase” by substituted-N-carboxymethyl dipeptides

Abstract A design effective for generating inhibitors of angiotensin converting enzyme has been successfully extended to inhibitors of another Zn ++ peptidase. A series of potent inhibitors for the zinc metalloendopeptidase associated with porcine kidney microsomes has been developed. Most contain the (S)-N-(1-carboxy-3-phenylpropyl)-L-Phe-X backbone. The most effective inhibitors with ID 50 values in the 10 −7 M range at pH 7.5 and 22°C were those where X = glycine, β-alanine, γ-amino butyric acid. A simple nomenclature designating substituted N-carboxy-methyl amino acid derivatives as -[N]- sharing amino acid derivatives is described.

Regio- and stereochemistry of the intramolecular [2+2] photoproducts from two related vinylogous imides

Abstract The regio- and stereochemistry of the intramolecular [2+2] photoproducts from two related vinylogous imides have been determined with the aid of X-ray crystallography; their chemistry and a mechanistic rationale of their formation are presented.

An examination of the extent of diasterofacial selection in the reactions of a chiral nitrile oxide with achiral alkenes: a route to β-hydroxy carboxylic acids

A new synthesis of optically active β-hydroxy carboxylic acids has been developed which is based on the (modest) diastereoselective addition of the chiral nitrile oxide (4) to 1,2-disubstituted alkenes.

An examination of π-facial selectivity in the diels-alder reaction of a chiral diene - a synthesis of (+)-5,6,10-tri-(EPI)-Actinobolin.

Abstract The π-facial course of the Diels-Alder reaction of an L-threonine derived silyloxydiene has been examined during the course of a study aimed at the total synthesis of actinobolin/bactobolin.

Enantioselection via birch reduction-alkylation of a chiral anthranilic acid derivative. Synthesis of enantiomerically pure aminocyclohexanes

Abstract The first method for preparation of enantiomerically pure aminocyclohexanes by Birch reduction-alkylation of a chiral anthranilic acid derivative is described; stereochemistry of alkylation is demonstrated by X-ray structural studies with 2b .