The localisations in liposomal membranes of the tetrahydrofuran ring moieties of the annonaceous acetogenins, annonacin and sylvaticin, as determined by 1H NMR spectroscopy.

The positions of the tetrahydrofuran (THF) ring moieties of annonacin (a mono-THF ring Annonaceous acetogenin) and sylvaticin (a non-adjacent bis-THF ring Annonaceous acetogenin) within liposomal membranes made of dimyristoylphosphatidylcholine (DMPC) were determined by proton (1H) nuclear magnetic resonance (NMR) spectroscopy. Based on 1H intermolecular nuclear Overhauser effects (NOEs), the THF rings of both acetogenins studied reside near the polar interfacial head group region of the DMPC. Recently, we have reported that the THF rings of a series of asimicin type of Annonaceous acetogenins (with adjacent bis-THF rings) also reside near the interfacial head group of DMPC. We can now conclude that the Annonaceous acetogenins, containing either mono-, adjacent bis-, or non-adjacent bis-THF ring moieties, have their THF ring moieties at the interfacial region of membranes, i.e., the THF ring moiety seems to serve a role as an anchor in the lipid membranes. This may be related to the uniquely potent bioactivities that Annonaceous acetogenins exhibit at their enzyme-inhibitory sites within mitochondrial and plasma membranes.

Membrane conformations and their relation to cytotoxicity of asimicin and its analogues.

Certain plant species belonging to the family Annonaceae produce Annonaceous acetogenins, which are a unique class of long-chain fatty acid derivatives with potent cytotoxicity. Putative protein targets of the acetogenins are membrane-associated proteins, including complex I. Asimicin and its analogues constitute a class of Annonaceous acetogenins containing two tetrahydrofuran (THF) rings with hydrocarbon chains tethered to each ring; an alpha,beta-unsaturated gamma-lactone ring is terminal to one of the alkyl chains. The compounds examined in this study differ in the length of the alkyl chain between the THF rings and the lactone ring. The positions of both the THF and the lactone rings within liposomal membranes were determined by proton (1H) nuclear magnetic resonance spectroscopy. The depth of membrane penetration of acetogenins, coupled to membrane diffusion, controls the conformation of acetogenins as they diffuse to an active site. Based on 1H intermolecular nuclear Overhauser effects (NOEs), the THF rings of all acetogenins studied reside near the polar interfacial head group region of the DMPC. This was corroborated by 1H two-dimensional NOE spectroscopy and differential scanning calorimetry studies. The 1H difference NOE spectra indicated that the lactone rings of asimicin and parviflorin, the latter of which has two fewer carbons in its alkyl chain, are located below the glycerol backbone in the membrane. In contrast with asimicin and parviflorin, the lactone ring of longimicin B, an asimicin analogue with an alkyl chain four carbons shorter, resides close to the midplane in the membrane. This was corroborated by manganese-induced broadening studies. Since the THF rings are located near the center of the acetogenin molecules and the lactone ring is terminal to a long alkyl chain, these observations indicate that an asimicin-type acetogenin can be in either sickle-shaped or U-shaped conformations, depending on the length of the alkyl chain between the THF rings and the lactone ring. Interestingly, longimicin B does not exhibit significant cytotoxicity, but parviflorin is as cytotoxic as asimicin. The cytotoxicity of the asimicin-type of acetogenins would seem to be strongly related to the membrane conformation. This is the first report elucidating the conformation of Annonaceous acetogenins in membranes.

New bioactive triterpenoids from Melia volkensii.

Bioactivity-directed fractionation of the root bark of Melia volkensii resulted in the isolation of two new natural products, meliavolkinin (1) and melianin C (3), together with two known compounds, 1,3-diacetylvilasinin (2) and melianin B (4). Jones oxidation of 4 gave compounds 3, 23,24-diketomelianin B (5), and 16,23,24-triketomelianin B (6). The structures of the new compounds were elucidated by spectral and chemical data. Compounds 1-6 all showed marginal cytotoxicities against certain human tumor cell lines, while 5 showed selective cytotoxicities for the human prostate (PC-3) and pancreatic (PACA-2) cell lines with potencies comparable to those of adriamycin.

Novel mono-tetrahydrofuran ring acetogenins, from the bark of Annona squamosa, showing cytotoxic selectivities for the human pancreatic carcinoma cell line, PACA-2.

The bark of Annona squamosa yielded three new mono-tetrahydrofuran (THF) ring acetogenins, each bearing two flanking hydroxyls and a carbonyl group at the C-9 position. These compounds were isolated using the brine shrimp lethality assay as a guide for the bioactivity-directed fractionation. (2,4-cis and trans)-Mosinone A (1) is a mixture of ketolactone compounds bearing a threo/trans/threo ring relationship and s double bond two methylene units away from the flanking hydroxyl. The other two new acetogenins differ in their stereochemistries around the THF ring; mosin B (2) has a threo/trans/erythro configuration across the ring, and mosin C (3) possesses a threo/cis/threo relative stereochemistry. Also found was annoreticuin-9-one (4), a known acetogenin that bears a threo/trans/threo ring configuration and a C-9 carbonyl and is new to this species. The structures were elucidated based on spectroscopic and chemical methods. Compounds 1-4 all showed selective cytotoxic activity against the human pancreatic tumor cell line, PACA-2, with potency 10-100 times that of Adriamycin.

Bioactive compounds from Taiwania cryptomerioides.

Two new sesquiterpenes, 10 alpha-hydroxyamorphan-4-en-3-one (1) and 4 alpha-methylcadinane-4 alpha-methyl-1 alpha,2 alpha,10 alpha-triol (2), together with four known compounds, sesquiterpenes 10 alpha-hydroxycadinan-4-en-3-one (3) and alpha-cadinol (4), diterpene ferruginol and lignan helioxanthin, were isolated from the whole plant of Taiwania cryptomerioides under bioassay-guided fractionations. The structures of 1 and 2 were elucidated mainly by the NMR spectroscopic analyses. Bioactivities of the isolated compounds against brine shrimp, yellow fever mosquito larvae, and human tumor cells are reported; compound 4 was the most bioactive, showing selectivity for the human colon tumor cell line (HT-29).

Venezenin: a new bioactive Annonaceous acetogenin from the bark of Xylopia aromatica.

Asimicin and a new cytotoxic Annonaceous acetogenin, venezenin [1], were isolated from the bark of Xylopia aromatica by bioactivity-directed fractionation using lethality to brine shrimp. Compound 1 represents an unusual type of C37 Annonaceous acetogenin, lacking either tetrahydrofuran (THF) or epoxide rings and possessing a double bond located two methylenes away from a vicinal diol in the hydrocarbon chain. The structure of 1 was elucidated by 1H- and 13C-nmr, COSY, single-relayed COSY, and by HMBC techniques, and derivatization. Annomontacin 10-one [6] and 18/21-cis-annomontacin-10-one [7], two semi-synthetic mono-THF acetogenins were prepared from 1. These acetogenins showed cytotoxicity, comparable or superior to adriamycin, against three human solid tumor cell lines. Reduction of the 10-keto of 1 to the racemic OH-10 derivative enhanced the bioactivity, as did the conversion of 1 to 6 and 7. Venezenin [1], like other Annonaceous acetogenins, showed inhibition of oxygen uptake by rat liver mitochondria and demonstrated that the THF ring may not be essential to this mode of action.

Bioactive neolignans from Endlicheria dysodantha.

From bioactivity-directed fractionation of the EtOH extract of Endlicheria dysodantha, dysodanthin A and dysodanthin B, which are new hexahydrobenzofuranoid neolignans, have been isolated. In addition, the known neolignans, compound 4, which is a burchellin analogue, and megaphone acetate [1] were isolated. All four neolignans showed activities in the brine shrimp lethality test; compounds 1-3 also inhibited the growth of crown gall tumors on potato discs and were cytotoxic to human tumor cells in culture. This is the first report of these neolignans isolated from the genus Endlicheria and of their completely assigned 1H-and 13C-nmr data.

Scintigraphic diagnosis of tricuspid regurgitation.

The authors describe a simple technique for diagnosis of tricuspid regurgitation. Red blood cells were labeled in vivo with 99mTc and 22 patients were studied with ECG-gated blood-pool imaging of the liver. A single region of interest was manually drawn around the liver and a time-activity curve obtained. The per cent change in liver counts during the cardiac cycle was found to be significantly higher in the 12 patients with tricuspid regurgitation (Group I) (mean, 4.04 +/- 1.6%; range, 1.3-21.4%) compared with the 10 controls (Group II) (mean, 0.35 +/- 0.16%; range, 0.013-1.3%) (p less than 0.05). Using a 1% change in liver counts as the criterion of a positive study, all 12 cases in Group I were diagnosed correctly, but there was one false positive in Group II; thus the sensitivity was 100% and the specificity 90%.

Aluminum chlorohydrate I: Structure studies.

X-ray diffraction and IR and 27AI-NMR spectroscopy indicate that aluminum chlorohydrate is composed of a central aluminum in a tetrahedral configuration surrounded by 12 aluminum atoms in octahedral configuration. The complex, AI13O4(OH)24(H2O)7+12, is essentially spherical, with the +7 charge equally distributed on the surface. Seven chloride ions are associated with the complex as counterions. This structure is consistent with both the method of synthesis and the proposed mechanism of antiperspirant activity.

Applicability of the phosphorus-31 (oxygen-17) nuclear magnetic resonance method in the study of enzyme mechanism involving phosphorus.

The phosphorus-31 (oxygen-17) [31P (17O)] NMR method [Tsai, M.-D. (1979) Biochemistry 18, 1448-1472] is tested for its general applicability by correlation with the line widths of the 17O NMR signals for the following compounds: trimethyl [17O4]phosphate (1), [17O4]phosphate (2), [alpha-17O2]adenosine 5'-(thiophosphate) (3), [alpha-17O, alpha beta-17O]-adenosine 5'-(1-thiotriphosphate) (4) [gamma-17O3]adenosine 5'-triphosphate (5), [alpha beta, beta gamma-17O2, beta-17O2]adenosine 5'-triphosphate (6), magnesium [gamma-17O3]adenosine 5'-triphosphate (7), and magnesium [alpha beta, beta gamma-17O2, beta-17O2]adenosine 5'-triphosphate (8). It is found that the line broadening effect of 17O on the 31P signals of the directly bonded 31P nuclei is present for all the functional groups in the above compounds which include examples of small 17O line widths (1 and 2), of intermediate 17O line widths (3, 5, and the nonbridge 17O of 4 and 6), and of very large 17O line widths (7, 8, and the bridge 17O of 4 and 6). On the basis of the established approximate relationship delta chi delta Q approximately aJ2, where delta chi and delta Q are the 31P and 17O line widths, respectively, of the 31P-17O groups, alpha is a constant, and J is the 31P-17O coupling constant, the results suggest that for most of the phosphate derivatives of biochemical interest, the line broadening effect of 17O should be present and detectable; i.e., delta chi should be larger than the limiting value (approximately 20 Hz). It is also found that Mg2+ causes the 17O signal of 5 and 6 to broaden (delta Q increases), which in turn causes the 31P signal to sharpen (delta chi decreases). The finding suggests that the 31P (17O) NMR methods, in combination with 17O NMR, could become a tool to study diamagnetic metal ion-nucleotide interactions.