Richard N. Sheppard

An x-ray crystallographic, mass spectroscopic, and NMR study of the limonoid insect antifeedant azadirachtin and related derivatives

Abstract The limonoid insect antifeedant azadirachtin (1) may be partially hydrogenated at the C22-C23 position and subsequently treated with an excess of sodium periodate and potassium permanganate in the presence of a base to give detigloyldihydroazadirachtin (4). This compound was examined by X-ray crystallographic techniques which revealed key structural fragments and together with detailed n.m.r. and mass spectroscopic studies allowed the complete unambiguous structure assignment to the parent azadirachtin molecule. Two further compounds, 3-deacetyl-11-desoxyazadirachtin (2), and 3-acetoxy-7-tigloyl-vilasinin lactone (3) were also isolated and characterised from a Senegal sample of neem seed.

A highly convergent total synthesis of the spiroacetal macrolide (+)-milbemycinβ1

Abstract A highly convergent synthesis of the macrolide natural product milbemycin β1 is reported. The key features of this synthesis include the introduction of the C11-C15 side chain by selective ring opening of a symmetrical 1,4-pentane bis-epoxide (3) followed by reaction with the anion derived from the 2,3-trans-dimethyl-6-phenylsulphonyl pyran (2) to afford the “northern” C11-C25 fragment (33) of milbemycin β1. Coupling of the derived C11-C25 aldehyde unit (37) with a C1-C10 southern zone fragment (5) was achieved via a novel deconjugative vinyl sulphone anion sequence to give a product containing all the carbon substituents of the natural product. Final manipulations involved macrolactonisation and subsequent introduction of the important 3,4-double bond by selenoxide syn-elimination. Methylation of the C-5 hydroxyl group was accomplished as the penultimate step with methyl iodide and silver (I) oxide under ultrasonication.

Neo-clerodane insect antifeedants from Scutellaria galericulata

Abstract Four neo-clerodane diterpenoids have been isolated from aerial material of Scutellaria galericulata . Three compounds, jodrellin T, 14,15-dihydrojodrellin T and galericulin, are novel structures. The fourth, jodrellin B has been previously isolated from Scutellaria woronowii . Jodrellin B is amongst the most potent neo-clerodane antifeedants so far described, 14,15-dihydrojodrellin T is also active. Chemical structures were rigorously determined by spectroscopic methods.

Chickpea blight: Production of the phytotoxins solanapyrones A and C by Ascochyta rabiei

Abstract Filtrates from 12-day-old stationary cultures of Ascochyta rabiei grown on Czapek-Dox medium, supplemented with an extract of chickpea seed, killed the cells in cell suspensions obtained by enzymic digestion of chickpea leaflets. Two toxins were isolated by solvent partitioning with ethyl acetate and flash chromatography of the organic fraction on silica. Mass spectrometry, UV, 13 C/ 1 H NMR and X-ray analysis showed that the two compounds were identical to the phytotoxins solanapyrones A and C isolated previously from culture filtrates of the fungus Alternaria solani .

The structure of two new clerodane diterpenoid potent insect antifeedants from Scutellaria woronowii (Juz); Jodrellin A & B

Abstract Two new clerodane diterpenoids isolated from Scutellaria woronowii (Juz) were shown to be the most potent clerodane antifeedants yet discovered. Their structures were rigorously determined by 1 H, 13 C, nuclear Overhauser difference 1-D, 1 H COSY 2-D n.m.r. and mass spectroscopy.

Chemistry of insect antifeedants from azadirachta indica (part 8): Synthesis of hydroxydihydrofuran acetal fragments for biological evaluation and azadirachtin total synthesis studies.

The work describes a unified strategy towards the preparation of model hydroxydihydrofuran acetal fragments (2) (3) and (45) common to the potent insect antifeedant and growth disruption agent azadirachtin (1). These units, along with other analogues, were prepared for biological evaluation as antifeedants. Furthermore, several potential coupling fragments (51), (52), (54), (55), (62), (63) and (56) for azadirachtin synthesis were also prepared from common precursors. Methods were developed to prepare these materials in enantiomerically pure form and to conveniently protect the angular hydroxyl group and unmask the labile enol double bond at a late stage in the synthesis.

Second- and third-row transition-metal complexes of dihydroxybenzoic acids, and the crystal structure of [NMe4]2[MoO2(2,3-dhb)2]·1.5H2O (2,3-H2dhb = 2,3-dihydroxybenzoic acid)

The new complexes [MO2L2]2–(H2L = 2,3- or 3,4-dihydroxybenzoic acid, 2,3-H2dhb or 3,4-H2dhb, M = Mo, W or Os; H2L = 2,6-dihydroxybenzoic acid, 2,6-H2dhb, M = Mo), [OsO2(py)2(2,6-dhb)](py = pyridine), [ReOl(PPh3)2L](H2L = 2,3-, 3,4- or 2,6-H2dhb) and [M(PPh3)2(2,3-dhb)](M = Pd or Pt) have been prepared. The crystal structure of [NMe4]2[MoO2(2,3-dhb)2]·1.5H2O has been determined and exhibits catecholato rather than salicylato type bonding. Infrared, Raman, 1H and 13C-{1H} NMR spectroscopic data for the complexes are also presented.

Trimethyl and diethylphenylphosphine complexes of rhenium(I, III, IV, V) and their reactions. X-ray crystal structures of a bis(η5-cyclopentadienyl)-ethane-bridged dirhenium(I) complex obtained from phenylacetylene, tetrakis-(diethylphenylphosphine) (dinitrogen) hydridorhenium (I), tetrakis(trimethyl-phosphine) (η2-dimethylphosphinomethyl) rhenium(I) and tetrakis(trimethylphosphine) (iodo)methyl rhenium(III) iodide-tetramethylphosphonium iodide

Abstract A number of trimethyl- and diethylphenylphosphine complexes of rhenium have been obtained by sodium amalgam reduction of ReCl4(THF)2 on from Re(NPh)Cl3(PMe3)2 and their reactions studied. The following compounds have been isolated and characterised by infrared and nuclear magnetic resonance spectroscopy. ReCl(PMe3)5 (A), ReH(PMe3)5 (B), [ReHCl(PMe3)5]BF4 (C), [Re(N2)(PMe3)5]Cl·MeOH (D), and the corresponding BF4− salt, [Re(PMe3)5]Cl (E), ReMe(PMe3)5 (F), ReCl(CO)2(PMe3)3 (G), [(Me3P)3Re(η5− C5H2Ph2)]2C2H2Ph2 (H), ReCl(N2)(PEt2Ph)4 (I), ReH(N2)(PEt2Ph)4 (J), [Re(NHPh)I(PMe3)4]I (K), Re(NHPh)(η2-CO2)(PMe3)3 (L), Re(η2 -CH2PMe2)(PMe3)4 (M), ReH3(PMe3)4 (N), [ReH4(PMe3)4]BF4(O) and [ReI(Me)(PMe3)4]I·[Me4P]I (P). For Re(η2-CH2PMe2)(PMe3)4 computer simulated and two dimensional δ/J resolved 31P{1H} NMR spectra have been obtained; the spectra are fully consistent with the structure determined by X-ray diffraction. The X-ray structures of compounds H,J,M and P have been determined. Preliminary data for compound C have also been obtained.

Manganese as a calcium probe: electron paramagnetic resonance and nuclear magnetic resonance spectroscopy of intact cells.

SummaryWhen Lettree cells are exposed to Mn2+, the cation becomes associated with cells in two ways: in a relatively loose and mobile manner that gives a six-line EPR spectrum designated Mnb*, and in an immobile, relatively tight manner that gives no detectable EPR spectrum, designated Mnb. Mnb* is probably on the surface of cells; most Mnb is probably inside cells. NMR measurements of Lettree cell suspensions show two water proton relaxation rates and confirm the existence of cell-associated Mn. Human erythrocytes, on the other hand, bind no Mn2+ under these conditions, as judged by EPR and NMR measurements.Virally-treated Lettree cells show an increase in Mnb (but not in Mnb*). They also show a third water proton relaxation rate.

Chemistry of insect antifeedants from Azadirachta indica (part 11): Characterisation and structure activity relationships of some novel rearranged azadirachtins.

Several novel rearrangement reactions of the natural product azadirachtin and related derivatives have been characterised using a combination of x-ray crystallographic and high field nmr techniques. The insect antifeedant properties of these and a number of C7 modified compounds have been investigated.