Petrus H. van Rooyen

Structure elucidation of fusarin C, a mutagen produced by Fusarium moniliforme

The assignment of structure (1) to fusarin C, a mutagen isolated from cultures of Fusarium moniliforme is based on a detailed study of its high-field 1H and 13C n.m.r. spectra and X-ray crystallography of the 8Z isomer of (1) which defined the substitution pattern and relative configuration of the 2-pyrrolidone moiety; nuclear Overhauser enhancement experiments indicate that the 2E,4E,6E,8E,10E polyene chromophore of (1) exists in solution as an equilibrium between two conformers with s-cis and s-trans topology of the C-5–C-6 single bond.

The isolation, structure, and absolute configuration of the mycotoxin, rhizonin A, a novel cyclic heptapeptide containing N-methyl-3-(3-furyl)alanine, produced by Rhizopus microsporus

Rhizonin A, the main mycotoxin from Rhizopus microsporus, is a cyclic heptapeptide containing valine, allo-isoleucine, leucine, N-methylalanine, N-methyl-3-(3-furyl)alanine (2 : 1 : 1 : 1 : 2), its amino-acid sequence having been established by mass spectrometry; X-ray crystallography verified the structure of rhizonin A and afforded its conformation and relative configuration, and its absolute configuration was obtained from high performance liquid chromatographic studies of the dansyl-derivatised amino-acids.

Reduction products of dinuclear [Rh2Cl2(CO)2 {μ-(PhO)2PN(Et)P(OPh)2}2]. Crystal structure of [Rh2HgCl(μ-H)(CO)2 {μ-(PhO)2PN(Et)P(OPh)2}2]

Abstract Treatment of [Rh 2 Cl 2 (CO) 2 {μ-(PhO) 2 PN(Et)P(OPh) 2 } 2 ] with various reducing agents gives a number of products, the type depending on the conditions employed. The products isolated include [Rh 2 (CO) 2 {μ-(PhO) 2 PN(Et)P(OPh) 2 } 2 ], [Rh 2 (CO) 3 {μ-(PhO) 2 PN(Et)P(OPh) 2 } 2 ],and [Rh 2 HgCl(μ-H)(CO) 2 {μ-(PhO) 2 PN(Et)P(OPh) 2 } 2 ]; the structure of the last complex was determined by X-ray diffraction.

Chiral thiophene dioxides and thiophene S,N-ylides as dienes for asymmetric diels-aldlr application

Abstract 2-Menthyltrihalothiophene S,S-dioxides are efficient asymmetric dienes in Diels-Alder reactions with dienophiles to give regio- and stereoisomerically pure adducts. Thus styrene, allyl alcohol, methyl acrylate and acrylamide give solely one adduct while flat dienophiles such as indene and acenaphthylene give two diastereomers. Analogous 1- and 3- chirally substituted thiophenes are of little value in generating pure single adducts. Further transformations of the above adducts into useful enantiomerically pure compounds is briefly discussed.

Distinctive chemo- and stereo-selective reactions of [Fe(CO)2Cp]+ and [AuPPh3+ with the anionic thioketene complex, [W(CO)5&[;C(OEt)(Ph)C(Ph)=C=S&];]−. Crystal structures of Z-[W(CO)5&[;C(SFe[CO]2Cp)C(Ph)=C(OEt)Ph&];] and E-[W(CO)5&[;S=C(AuPPh3)C(Ph)=C(OEt)Ph&];]

Abstract Reaction of the unusual thioketone adduct [W(CO) 5 &[;C(OEt)(Ph)C(Ph)=C=S&];]Li with [Fe(CO) 2 CpI] gives two binuclear tungsten iron complex isomers of composition [W(CO) 5 &[;C(SFe[CO] 2 Cp)C(Ph)=C(OEt)Ph&];] that differ only in the position of the iron substituent at the extremely short C(carbene)S bond. Crystallization affords only the isomer in which the metal atoms are oriented trans , as is shown by the X-ray crystal structure. Both isomers have a Z configuration about the C=C double bond. Treatment of the same adduct with [AuC/PPh 3 ] affords a binuclear compound in which the tungsten and gold atoms are linked by a thione group. This conversion is also stereo-selective with regard to the alkene bond and only the E isomer is formed. The structure of the product [W(CO) 5 &[;S=C(AuPPh 3 )C(Ph)=C(OEt)(Ph)&];] was determined by X-ray diffraction. Comparison of structural features with the related thioaldehyde complex, E -[W(CO) 5 &[;S=CHC(Ph)=C(Ph)(OEt)&];] reveals the significant electron-withdrawing effect of the gold fragment.

Crystal structures and conformational analysis of ochratoxin A and B: probing the chemical structure causing toxicity

Studies performed on two metabolites from Aspergillus ochraceus, ochratoxin A (1) and B (2), have yielded information related to the steric, conformational, and electronic considerations that could contribute to the different toxicities of these metabolites. The relative HCl-catalysed hydrolysis rates of the toxins are reversed compared with those observed in biological systems. This reversal of relative rate is ascribed to steric hindrance due to the chloro group in ochratoxin A (1). Single-crystal X-ray structural analyses, i.r., and high field n.m.r. analysis indicate no discernible difference in conformations.

Novel α-methyldeoxybenzoins from the heartwood of Pterocarpus angolensis D.C.: absolute configuration and conformation of the first sesquiterpenylangolensis, and X-ray crystal structure of 4-O-α-cadinylangolensin

The known 2,4-dihydroxy-4′-methoxy-α-methyldeoxybenzoin, (αR)-angolensin, is accompanied by the novel (αS)-4-O-methylangolensin and a unique epimeric pair comprising (αR,1″R,4″S,4″aR,8″aR)-4-O-α-cadinylangolensin and (αR,1″S,4″S,4″aR,8″aR)-4-O-T-cadinylangolensin in the heartwood of Pterocarpus angolensis D.C. The absolute configuration and conformation of the former was determined by X-ray analysis.Bis-(2-ethylhexyl) phthalate accompanies the above metabolites.

Dinuclear hydride and η3-bonded dithioformate complexes of iron(II)

Iron(II) chloride reacts consecutively with bis(diphenylphosphino)methane (dppm), activated magnesium and cyclopentadiene to give the mono- and di-iron hydrides [FeH(η-C5H5)(dppm)]1 and [{Fe(η-C5H5)}2(µ-H)(µ-PPh2)(µ-dppm)]2. Compound 2 contains three bridging units (average separation of the hydride from the metal atoms, 1.73 A) in the solid state and crystallizes in the space group P21/c with a= 10.004(2), b= 20.134(7), c= 19.353(10)A, β= 95.00(3)° and Z= 4. Compound 1 reacts with CS2 to form the dithioformate complex [Fe(η-C5H5)(dppm-P)(S2CH)]4. The sulfur-donor ligand is η3 co-ordinated in solution.

Synthesis and crystallographic characterization of thiazolyl and thiazolinylidene complexes of cyclopentadienyliron(II)

The consecutive reaction of FeCl2 with bis(diphenylphosphino)methane or 1,2-bis(diphenylphosphino)ethane, benzothiazol-2-yllithium or 4-methylthiazolyllithium and cyclopentadiene affords thiazolinylidene(thiazolyl) complexes which contain only one co-ordinated phosphorus atom. An X-ray crystal structure determination of one of these, [Fe(η5-C5H5)([graphic omitted]-o)([graphic omitted]-o)(dppe)], has revealed a metal–carbene carbon bond length of 1.889(3)A and a hydrogen bond between the nitrogen atoms in the two neighbouring carbene and benzothiazolyl ligands. Cationic thiazolinylidene complexes form when the products from the reaction between [Fe(η5-C5H5)(CO)2Cl] and benzothiazol-2-yllithium or 4-methylthiazolyllithium are acidified with trifluoromethanesulfonic acid. A single crystal X-ray structure determination of [Fe(η5-C5H5)(CO)2{[graphic omitted]}]CF3SO3·0.5H2O showed a metal–carbene carbon bond length of 1.947(3)A which is longer than all the Fe–C(carbonyl) distances (average 1.768 A).

π-Arene complexes: II. Synthesis, characterization and reactivity towards arene and thioether substitution of π-arenedicarbonyl(thioether)chromium(0)complexes. Crystal structure of cis-tetracarbonyl(methyl-1,3-dithian-2-methyl-2-dithiocarboxylate)chromium(0)

Abstract A carbonyl ligand of π-arenetricarbonylchromiun(0) complexes is photochemically displaced to give π-arenedicarbonyl complexes of chromium(0) with thio-ether ligands. In contrast, irradiation of π-arenetricarbonylchromium compounds with dithio-ester and trithiocarbonate ligands yields only pentacarbonyl complexes. Substitution of the π-arene ring, the thio-ether ligand, or both, is easily achieved at room temperature and in polar solvents. The crystal structure of cis -tetracarbonyl(methyl-1,3-dithian-2-methyl-2-dithiocarboxylate)chromium(0) shows remarkably similar CrS bond distances of 2.379(2) and 2.383(2) A for the respective thio-ether and dithio-ester sulphur-donor atoms of the bidentate ligand.