Clifford J. Hawkins

Cycloxazoline : a cytotoxic cyclic hexapeptide from the ascidian Lissoclinum bistratum

Abstract The isolation of a new cyclic hexapeptide is reported from a marine ascidian Lissoclinum bistratum. The structure was determined by NMR, mass spectrometry and X-ray crystallographic techniques. Cytotoxicity against MRC5CV1 and T24 cells expressed as IC50 was 0.5 μg/mL.

Conformational analysis of coordination compounds. XI. Molecular structure of tetraammine{(±)-pentane-2,4-diamine)cobalt(III) dithionate

The crystal structure of tetraammine{(±)-pentane-2, 4-diamme)cobalt(III) dithionate dihydrate [Co{(±)-ptn)(NH3)4] (S2O6)1·5, 2H2O has been determined by X-ray structure analysis. The crystals are triclinic with the space group PĪ, with a 11·43, b 11·65, c 7·78 A, α 100·48°, s 105·95°, and y 75·95°. The structure has been refined by least-squares methods with anisotropic temperature factors to an R value of 0-043 for 2654 reflections. The six-membered diamine chelate ring has a skew-boat conformation in which the two methyl groups are in equatorial orientations. A strainenergy-minimization calculation for the complex reveals an energy difference of 8·3 kJ mol-1 between the preferred skew-boat conformation and the chair conformation. The calculated minimum-energy geometry for the skew-boat conformation is in good agreement with the observed structure for the chelate ring in the dithionate salt. The 1H n.m.r. spectra of this complex and other complexes of the chiral isomer of pentane-2, 4-diamine are discussed in terms of the observed structures and the conformational analysis.

Vanadium content and oxidation state related to ascidian phylogeny

Abstract 1. 1. New atomic absorption and electron spin resonance (e.s.r.) analyses of 50 ascidian species together with published information on other species demonstrates that when vanadium is found in the ascidian suborder Aplousobranchia, it is present as vanadium(IV); in the Phlebobranchia, vanadium is present as vanadium(III); and no significant amounts of vanadium are present in the Stolidobranchia. 2. 2. Vanadium e.s.r. analysis confirms Cionidae as a family of the Aplousobranchia, and an independent origin of the Didemnidae from an early ancestral stock is implied by the high level of vanadium(IV) in the genus Leptoclinides ; loss of vanadium is associated with evolutionary trends. 3. 3. A reconstruction of ascidian phylogeny is based on morphology and vanadium chemistry.

Isolation of 3,4-dihydroxyphenylalanine-containing proteins using boronate affinity chromatography

A rapid procedure for the isolation of 3,4-dihydroxyphenylalanine-containing proteins has been developed in which the protein is selectively bound to a m-phenylboronate agarose column, and eluted with 1.0 M ammonium acetate, pH 3.0. The method is based on the affinity of boronates for diols including catechol. The chromatography is carried out in the absence of oxygen to prevent oxidation of the catechol. Other proteins are eluted beforehand with 0.25 M ammonium acetate, pH 8.5, or for glycoproteins with a Tris buffer containing 0.2 M sorbitol, pH 8.5.

Vanadium chemistry of ascidians

Abstract 1. 1. Addition of exogenous ligands, 2,2′-bipyridine and 1,10-phenanthroline, to a variety of aplousobranch and phlebobranch ascidians, oproduced deep purple oxo-bridged binuclear complexes of bis(chelate)vanadium(III) within compartment (including signet ring) and some unpigmented morula cells confirming the presence of vanadium(III) in these cells. 2. 2. Treatment with acetylacetone formed [VO(acac) 2 ] and [V(acac) 3 ]. 3. 3. Electron paramagnetic resonance studies confirmed the presence of vanadium(IV) in all vanadium-containing Aplousobranchs, and little or no vanadium(IV) in the Phlebobranchs, and identified two types of vanadium(IV) binding to organic ligands with the ‘oxidized’ Phlebobranchs generally of Type I and the Aplousobranchs generally of Type II with e.p.r. parameters: Type I— g x 1.992, g y 1.987, g z 1.967, A x 53.01, A y 51.95, A z 155.47 × 10 4 cm −1 ; Type II— g y 1.980, g y 1.985, g z 1.951, A x 59.08, A y 55.72, A x 166.68 × 10 4 cm −1 . 4. 4. Electron microscopic investigation of the morula cells of the phlebobranch, Ecteinascidia nexa , showed that the intracellular globules were rich in vanadium.

The bistratenes: new cytotoxic marine macrolides which induce some properties indicative of differentiation in HL-60 cells.

The biological effects of cytotoxic macrolide polyethers, the bistratenes, isolated from the ascidian Lissoclinum bistratum, have been examined. Bistratene A was toxic to HL-60 human promyelocytic leukemia cells with an IC50 value of 424 nM. At lower concentrations (10-100 nM), bistratene A induced the incomplete differentiation of these cells along the monocyte/macrophage pathway. These effects were not due to inhibition of DNA synthesis. Bistratene B had similar effects to bistratene A. At micromolar concentrations these compounds enhance the phospholipid-dependent activity of type II protein kinase C from bovine spleen. The bistratenes provide new probes for studying the molecular mechanisms governing cell growth and differentiation.

Conformational analysis of coordination compounds. VI.* P.M.R. study of diamagnetic five-membered diamine chelate rings

The proton magnetic resonance spectra of a number of coba1t(III), molybdenum(0), chromium(0), platinum(II) and palladium(II) complexes of (R)-propane-1, 2-diamine, (S)-3, 3-dimethylbutane-1, 2-diamine, (RS)-N, N, N’, N’-tetramethylpropane-1, 2-dime and ethane-1, 2-diamine have been analysed and the coupling constant data utilized to calculate the conformational populations for the various complexes. Necessary parameters for the conformational analysis were obtained from a study of tetracyano{(S)-3, 3-dimethylbutane-1, 2-diamine}cobaltate(III), in which the t-butyl group was assumed to be exclusively in the equatorial orientation. The preparation and resolution of this t-butyl substituted ethane-1,2-diamine are described.

Comparative study of the blood plasma of the ascidians Pyura stolonifera and Ascidia ceratodes

The components of the blood plasma of the ascidians, Pyura stolonifera and Ascidia ceratodes, have been separated by Sephadex G75 chromatography and gel electrophoresis. The absorption spectra of the plasma and the fractions for both species and the corresponding circular dichroisni spectra for Pyura stolonifera have been recorded. The components for each species consisted of a number of proteins and two N-acetylaminosugar compounds, probably aminopolysaccharides. Although there were similarities in the properties of these components between the two species, a number of important differences were observed, especially with regard to the uptake of metals as studied by 59Fe, “?�Mn, 48V, and 51Cr radiotracers. Electron spin resonance measurements detected manganese ( I I ) in a N-acetylamino sugar component of the plasma of Pyura stolonif era.

CHEMISTRY OF THE BLOOD OF THE ASCIDIAN PODOCLAVELLA MOLUCCENSIS

The blood plasma of the aplousobranch Podoclavella moluccensis was found to have features similar to the plasma of ascidians from different suborders, including the presence of a yellow saccharide. The plasma concentrates a number of transition metals, especially vanadium, manganese, zinc, and chromium. The dominant blood cells were yellow morula cells and blue granular cells. A yellow ethanolic extract of the cells had a visible spectrum similar to a β-carotene with an additional intense absorption at about 270 nm. Magnesium and a trace of iron (III) were the only metals detected in that fraction. A subsequent purple acidified-ethanol extract, also possibly a carotenoid, and the cell residue contained a number of metals. Relative to the plasma, these two fractions concentrated calcium, and also iron, vanadium, and chromium, to a much greater extent than magnesium. This is the first report of chromium in the blood cells of ascidians or of significant concentrations of zinc in the plasma. The vanadium was ...

Intracellular acidity in the ascidian

1. 1. Morula cells of three Ascidiidae and two Perophoridae from the suborder Phlebobranchia, and one Holozoidae and one Clavelinidae from the suborder Aplousobranchia were acidic to neutral red; where methyl red was used, the stain corresponded to pH values between 4.6 and 6.0 depending on species. Five Didemnids (Aplousobranchia), and two Pyuridae, two Styelidae, and one Molgulidae (Stolidobranchia) had neutral morula cells. All compartment cells were neutral. 2. 2. Phosphorus-31 NMR spectrum of blood cells of Pyura stolonifera (Stolidobranchia) had Pi signals corresponding to pH 6.4 and 6.1, probably from phosphate within the globules and cytoplasm of the morula cells. The 31P NMR spectra of whole colonies of Diplosoma similis and Diplosoma virens had signals corresponding to Pi at pH values of 5.58 and 5.65. 3. 3. In Phlebobranchia, acid released by vanadocytes upon lysis could not be accounted for solely by the hydrolysis of V(III) and Fe(III), but within the vanadocytes the pH is too high for the metals to be in hydrated forms. 4. 4. Tunic acid was examined. The tunic cells of many species of Aplousobranchia and Phlebobranchia released acid on lysis but the intact cells were neutral.