Stereoselective reactions of (20R)-3,20-dihydroxy-(3',4'-dihydro-2'H-pyranyl)-5-pregnene derivatives form 27-nor-3,20,23,26-tetrahydroxy-cholesten-22-ones and related bromo ketones

The previously reported analog of pregnenolone having a 3,4-dihydro-2H-pyran attached via a Cz.sbnd;C bond to the C-20 position (1), stereoselectively reacts with m-chloroperoxybenzoic acid in methanol at -5 degrees C. Acid-catalyzed hydrolysis of the isolated intermediates gives good yields of mostly a new 27-norcholesterol analog: (20R,23R)-3,20,23,26-tetrahydroxy-27-norcholest-5-en-22-one-3-acetate (2a, and a smaller amount of its 23S enantiomer 2b). Three different conditions of epoxidation and methanolysis followed by acid-catalyzed hydrolysis typically produce approximately 2:1 ratios of the 23R:23S diastereoisomers with a C-23 hydroxy group at the new asymmetric center. Bromine also reacts stereoselectively with (20R)-3,20-dihydroxy-(3',4'-dihydro-2'H-pyranyl)-5-pregnene (4) giving mostly (20R,23R)-23-bromo-3,20,26-trihydroxy-27-norcholest-5-en-22-one (7a). Thus both major steroidal products 2a and 7a have the same C-23R configuration. Assignment of molecular structures and the absolute configurations to 1 and 2a were based on elemental analysis, mass spectra, nuclear magnetic resonance, FTIR infrared spectroscopic analysis and X-ray crystallography. Mechanisms are discussed for stereochemical selectivity during epoxidation and bromination of the 3,4-dihydro-2H-pyranyl ring in 1 and 4.     

Novel synthesis of cholesterol analogs: condensation of pregnenolone with dihydropyran or dihydrofuran.

Pregnenolone 3-(2'-tetrahydropyranyl) ether (1) was condensed with 3,4-[2H]dihydropyran to mainly give (20R)-[6'-(3',4'-[2'H]dihydropyranyl)]-pregn-5-ene-3 beta,20-diol 3-(2'-tetrahydropyranyl) ether (20R-3), according to nuclear magnetic resonance (NMR). Cold, dilute HCl in ethanol removed the tetrahydropyranyl group at C-3 and also opened the dihydropyranyl ring at the C-20 position of 20R-3 to give (20R)-27-norcholest-5-en-22-one-3 beta,20,26-triol (20R-5). Analogous results were obtained by condensing pregnenolone 3-acetate with 3,4-[2H]dihydropyran to provide (20R)-[6'-(3',4'-[2'H]dihydropyranyl)]-pregn-5-ene-3 beta,20-diol 3-acetate (20R-4). Acid-catalyzed opening of the dihydropyranyl ring at C-20 in 20R-4 yielded 20R-7, which, on acetylation followed by crystallization, provided (20R)-27-norcholest-5-en-22-one-3 beta,20,26-triol 3,26-diacetate (20R-8), identical to the diacetate made from 20R-5. Varying the reaction sequence beginning with 20(R,S)-4 gave an 84:16 ratio of 20R to 20S in a mixture of 20(R,S)-8, according to NMR analysis. Crystallization of the mixture from methanol provided pure 20R-8. Condensing 2,3-dihydrofuran and 1 for producing (20R)-[5'-(2',3'-dihydrofuranyl)]-pregn-5-ene-3 beta,20-diol 3-(2'-tetrahydropyranyl) ether (6) gave instead (20R)-26,27-bisnorcholest-5-en-22-one-3 beta,20,25-triol 3-(2'-tetrahydropyranyl) ether (20R-9) by partial hydrolysis during workup. Treating 20R-9 briefly with dilute HCl produced (20R)-26,27-bisnorcholest-5-en-22-one-3 beta,20,25-triol (20R-10).(ABSTRACT TRUNCATED AT 250 WORDS)     

Sterol synthesis. Preparation and characterization of fluorinated and deuterated analogs of oxygenated derivatives of cholesterol.

Oxygenated sterols, including both autoxidation products and sterol metabolites, have many important biological activities. Identification and quantitation of oxysterols by chromatographic and spectroscopic methods is greatly facilitated by the availability of authentic standards, and deuterated and fluorinated analogs are valuable as internal standards for quantitation. We describe the preparation, purification and characterization of 43 oxygenated sterols, including the 4 beta-hydroxy, 7 alpha-hydroxy, 7 beta-hydroxy, 7-keto, and 19-hydroxy derivatives of cholesterol and their analogs with 25,26,26,26,27,27,27-heptafluoro (F7) and 26,26,26,27,27,27-hexadeuterio (d6) substitution. The 7 alpha-hydroxy, 7 beta-hydroxy, and 7-keto derivatives of (25R)-cholest-5-ene-3 beta, 26-diol (1d) and their 16,16-dideuterio analogs were also prepared. These d2-26-hydroxysterols and [16,16-2H2]-(25R)-cholest-5-ene-3 beta, 26-diol (1e) were synthesized from [16,16-2H2]-(25R)-cholest-5-ene-3 beta, 26-diol diacetate (2e), which can be prepared from diosgenin. The highly specific deuterium incorporation at C-16 in 1e and 2e should be useful in mass spectral analysis of 26-hydroxycholesterol samples by isotope dilution methods. The delta 5-3 beta, 7 alpha, 26- and delta 5-3 beta, 7 beta, 26-triols were regioselectively oxidized/isomerized to the corresponding delta 4-3-ketosteroids with cholesterol oxidase. Also described are 5,6 alpha-epoxy-5 alpha-cholestan-3 beta-ol, its 5 beta,6 beta-isomer, cholestane-3 beta, 5 alpha,6 beta-triol, their F7 and d6 derivatives, and d3-25-hydroxycholesterol, which was prepared from 3 beta-acetoxy-27-norcholest-5-en-25-one (30). The 43 oxysterols and most synthetic intermediates were isolated in high purity and characterized by chromatographic and spectroscopic methods, including mass spectrometry and nuclear magnetic resonance (NMR) spectroscopy. Detailed mass spectral assignments are presented, and 1H NMR stereochemical assignments are derived for the C-19 protons of 19-hydroxysterols and for the side-chain protons of 30.     

Amorpha-4,11-diene synthase: mechanism and stereochemistry of the enzymatic cyclization of farnesyl diphosphate

Recombinant amorpha-4,11-diene synthase from Artemisia annua, expressed in Escherichia coli, was incubated with the deuterium-labeled farnesyl diphosphates, (1R)-[1-(2)H]FPP, (1S)-[1-(2)H]FPP, and [1,1-(2)H2]FPP. GC-MS analysis of amorpha-4,11-diene formed from the deuterated FPPs shows that the deuterium atoms are retained in the product. Furthermore, analysis of the MS-spectra obtained with the differently labeled substrate indicates that the H-1si-proton of FPP is transferred during the cyclization reaction to carbon 10 of amorphadiene while the H-1re-proton of FPP is retained on C-6 of the product. Proton NMR and COSY experiments proved that the original H-1si-proton of FPP is located at C-10 of amorpha-4,11-diene as a result of a 1,3-hydride shift following initial 1,6-ring closure. The results obtained support the previously suggested mechanism for the cyclization of farnesyl diphosphate by amorph-4,11-diene synthase involving isomerization of FPP to (R)-nerolidyl diphosphate (NPP), ionization of NPP, and C-1,C-6-ring closure to generate a bisabolyl cation, followed by a 1,3-hydride shift, 1,10-ring closure to generate the amorphane skeleton, and deprotonation at either C-12 or C-13 to afford the final product (1S,6R,7R,10R)-amorpha-4,11-diene.     

Substrate-dependent chemoselective aldose-aldose and aldose-ketose isomerizations of carbohydrates promoted by a combination of calcium ion and monoamines.

Epimerization of aldoses at C-2 has been extensively investigated by using various metal ions in conjunction with diamines, monoamines, and aminoalcohols. Aldoses are epimerized at C-2 by a combination of alkaline-earth or rare-earth metal ions (Ca(2+), Sr(2+), Pr(3+), or Ce(3+)) and such monoamines as triethylamine. In particular, the Ca(2+)-triethylamine system proved effective in promoting aldose-ketose isomerization as well as C-2 epimerization of aldoses. 13C NMR studies using D-(1-(13)C)glucose and D-(1-(13)C)galactose with the CaCl(2) system in CD(3)OD revealed that the C-2 epimerization proceeds via stereospecific rearrangement of the carbon skeleton, or 1,2-carbon shift, and ketose formation proceeds partially through an intramolecular hydrogen migration or 1,2-hydride shift and, in part, via an enediol intermediate. These simultaneous aldose-aldose and aldose-ketose isomerizations showed interesting substrate-dependent chemoselectivity. Whereas the mannose-type aldoses having 2,3-erythro configuration (D-mannose, D-lyxose, and D-ribose) showed considerable resistance to both the C-2 epimerization and the aldose-ketose isomerization, the glucose-type sugars having 2,3-threo and 3,4-threo configurations, D-glucose and D-xylose, are mainly epimerized at C-2 and those having the 2,3-threo and 3,4-erythro configurations, D-galactose and D-arabinose, were mostly isomerized into 2-ketoses. These features are of potential interest in relevance to biomimic sugar transformations by metal ions.     

24,26-Dihydroxyvitamin D2: a unique physiological metabolite of vitamin D2

A new vitamin D2 metabolite, 24,26-dihydroxyvitamin D2, has been detected in the plasma of rats fed physiologic amounts of vitamin D2. The identity of the new metabolite (isolated from cow plasma) was established by ultraviolet absorbance, mass spectroscopy, chemical reactivity, and NMR spectroscopy. Among these, the mass spectrum was unique for the presence of a peak at M-48 that was attributed to an intramolecular rearrangement involving both the C-24 and C-26 hydroxyl groups. A 300-MHz 1H NMR spectrum of 40 micrograms of metabolite indicated a downfield shift of the C-28 methyl group signal to delta 1.30 and a multiplet at delta 3.66 corresponding to the hydroxylated C-26 methyl group. We determined that the formation of 24,26-dihydroxyvitamin D2 represented a major pathway for further metabolism of 24-hydroxyvitamin D2 in rats, exceeding the formation of 24,25-dihydroxyvitamin D2. Standard bioassays revealed that 24,26-dihydroxyvitamin D2 possessed very little biological activity and most likely represents a deactivation pathway for 24-hydroxyvitamin D2.     

Base promoted air oxidation of 13beta-ethyl-11-methylenegon-4-en-17-one.

The structure of 13-ethyl-11-methylene-18,19-dinor-17alpha-pregn-4-en-20-yn-16beta,17-diol (3, 16beta-OH desogestrel), a by-product obtained in the last step of the synthesis of desogestrel (1) by reaction of monolithium acetylide-ethylenediamine complex with 13beta-ethyl-11-methylenegon-4-en-17-one (2), is here reported. The structural assignments were supported by NMR 1H-, 13C-, 1H-1H COSY, 1H-13C HSQC, COLOC) and mass spectroscopy, and the configuration at the C-16 and C-17 stereocentres was established by X-ray crystallography. When the same 17-ketoderivative 2 was treated with a non-alkylating base, such as potassium tert-butoxide, instead of the expected 16-hydroxylated ketone, a dimeric product, 13beta-ethyl-16-[2'-(des-D-13"-carboxy-13"beta-ethyl-11"-methylenegon-4"-en-14"-yl)-ethyliden]-11-methylenegon-4-en-17-one (4), was isolated in good yield; it was characterized by NMR, mass, ultraviolet spectroscopy, and chemical transformations. Compounds 3 and 4 originate from the high reactivity of the 16-methylenic position of the 17-keto substrate (2) toward molecular oxygen under basic conditions.     

The formation of a 1-5 phosphodiester linkage in the spontaneous breakdown of 5-phosphoribosyl-alpha-1-pyrophosphate

The decomposition of 5-phosphoribosyl-alpha-1-pyrophosphate (PRPP) in the presence of Mg2+ at pH=7.8 yields a combination of products including ribose 5-phosphate, ribose 1-phosphate, 5-phosphoribosyl 1,2 cyclic phosphate, inorganic phosphate, and pyrophosphate. Hydrogen decoupled 31P NMR analysis of the product mixture also exhibits a sharp peak (+2.6 ppm from phosphocreatine) in a chemical shift region which includes phosphodiester bonds. Alkaline phosphatase treatment of the product mixture results in cleavage of monophosphate esters such as ribose 1-phosphate and ribose 5-phosphate, but does not affect the unidentified peak. Homonuclear (1H) correlation spectroscopy (COSY) of a partially purified sample was successful in identifying the hydrogen spectra of this compound. Combined with results from the splitting patterns of selectively decoupled 31P spectra, the COSY data indicate that several hydrogens are directly coupled to the unknown phosphate group with J value matches to the hydrogen on carbon one and to the two hydrogens on carbon five. Heteronuclear (1H-31P) chemical shift correlation studies confirm these couplings and further substantiate the formation of a ribose 1-5 phosphate linkage during the degradation of PRPP under these conditions. It is presently unknown whether this is an intramolecular or intermolecular phosphodiester linkage, although some spectroscopic evidence suggest the intramolecular bond formation, i.e. a ribose 1,5-cyclic phosphate (R-1,5cP). The formation of R-1,5cP helps explain the observation that the 5-phosphate group from PRPP becomes labile during the spontaneous degradation of PRPP.     

Assigning stereodiversity of the 27-Me group of furostane-type steroidal saponins via NMR chemical shifts

Applicability of (13)C and (1)H NMR chemical shifts for the assignment of the 25R/25S configuration of the 27-methyl group in the case of furostane-type steroidal saponins has been investigated. A comparative study of (13)C NMR data suggest that chemical shift values for C-20, C-21, C-22, C-23, C-24, C-25, C-26 and C-27 resonances were not much influenced by R/S configuration of the 27-Me group, thus reflecting limited application of (13)C NMR chemical shifts for such stereochemical determinations. In contrast, (1)H NMR chemical shifts (delta(a), delta(b)) for geminal protons of glycosyloxy methylene (H(2)-26) exhibit pronounced dependence and the difference (Delta(ab)=delta(a)-delta(b)) among their chemical shifts [Delta(ab)= or <0.48 for 25R; Delta(ab)= or >0.57 for 25S] seems to be of general applicability for ascertaining 25R/25S orientation of the 27-methyl group of furostane-type steroidal saponins.     

Regioselective cleavage of rings E and F in sarsasapogenin

Sapogenins from the 25R and 25S series show a marked difference on the E/F regioselectivity of the spiroketal cleavage with BF(3)/Ac(2)O. In contrast to the high yield of single E-ring cleavage products from diosgenin (3) and hecogenin (5), sapogenins of the 25R series (equatorial C-27 methyl), sarsasapogenin (1, 25S series, axial C-27 methyl) yields the corresponding acetyldihydropyran, (25S)-23-acetyl-22,26-epoxy-5beta-cholest-22-ene-3beta,16beta-diyl diacetate (8), two isomeric furostenes: (E)- and (Z)-(25S)-23-acetyl-5beta-furost-22-ene-3beta,26-diyl diacetate (9 and 10) and a third one bearing an additional acetyl group: (E)-(20S,25S)-20,23-diacetyl-5beta-furost-22-ene-3beta, 26-diyl diacetate (11). The structures of the compounds were unambiguously established using two dimensional NMR techniques. The lower E/F selectivity in the cleavage of 1 is attributed to steric hindrance resulting from the axial methyl in F ring on a beta elimination forming the dihydropyran double bond in the major product 8.     

Recent development of asymmetric syntheses based on the Meerwein-Ponndorf-Verley reduction

Stereoselective Meerwein-Ponndorf-Verley (MVP) reductions, including intermolecular MPV reductions, intramolecular MPV reductions (asymmetric 1,5- and 1,7-hydride shifts), catalytic MPV reduction, and reactions related to the MPV reduction are reviewed from the standpoint of asymmetric synthesis.     

Fragments formed by the side chain cleavage of a 20-aryl analog of 20alpha-hydroxycholesterol by adrenal mitochondria.

An analog of 20alpha-hydroxycholesterol, (20R)-20-phenyl-5-pregnene-3beta,20-diol, which is completely substituted at C-22 was prepared with radioisotopes at various positions. The analog labeled with 3H at C-M and 14C at C-4 and C-IU was converted into radioactive pregnenolone by an enzyme preparation derived from adrenal mitochondria. Cleavage of the phenyl analog labeled with 3H in the aromatic ring by the same enzyme preparation led to the formation of [3H]phenol. Using the substrate doubly labeled with 14C at C-4 and 3H in the aromatic ring, it appeared that the products of the reactions, pregnenolone and phenol, were formed in equal amounts. During incubation of the side chain labeled substrate, another labeled fragment was formed. It was identified as acetophenone, a product resulting from cleavage of the C17,20 bond. The steroidal fragment corresponding to this C8 ketone was traced using nuclear label analog. From its nonpolar chromatographic properties it appears to be a C-17-deoxy-C19 steroid.     

Synthesis of 1-(5'-O-benzoyl-3'-deoxy-beta-D-glycero-pentofuran-2'-ulosyl)uracil and its alpha-anomer by [1,2]-hydride shift

In contrast with direct tosylation of 5'-O-benzoyl- (1d) or 5'-O-pivaloyl-1-beta-D-lyxofuranosyl-uracil (1e) with TsCl/pyridine, tosylation of the 2', 3'-O-dibutylstannylene derivatives (4d,e) of these compounds proved to give the 3'-O-tosyl derivatives 2d, e selectively. Coversion of 2d as a model to 1-(5'-O-benzoyl-3'-deoxy-beta-D-glycero-pentofuran-2'-ulosyl )uracil (5-beta) by base-induced [1,2]-hydride shift was examined under various reaction conditions, and the alpha/beta ratio of the product mixture (5-alpha, beta) determined by 1H NMR spectroscopy in each case. The BzOLi/DMF combination has proved to be most profitable for obtaining 5-beta.     

Cytotoxic triterpenoid saponins from the fruits of Aesculus pavia L

Continued chemical investigation on the fruits of North American Aesculus pavia L. resulted in the isolation and identification of 13 polyhydroxyoleanene pentacyclic triterpenoid saponins, named aesculiosides IIe-IIk (1-7), and IIIa-IIIf (8-13), together with 18 known compounds: aesculiosides Ia-Ie (14-18), IIa-IId (19-22), IVa-IVc (23-25), 3-O-[beta-D-galactopyranosyl(1-->2)]-alpha-L-arabinofuranosyl(1-->3)-beta-D-glucuronopyranosyl-21,22-O-diangeloyl-3beta,15 alpha,16 alpha,21 beta,22 alpha,28-hexahydroxyolean-12-ene (26), 3-O-[beta-D-glucopyranosyl(1-->2)]-alpha-L-arabinofuranosyl(1-->3)-beta-D-glucuronopyranosyl-21,22-O-diangeloyl-3beta,16 alpha,21 beta,22 alpha,24 beta,28-hexahydroxyolean-12-ene (27), 3-O-[beta-D-galactopyranosyl(1-->2)]-alpha-L-arabinofuranosyl(1-->3)-beta-D-glucuronopyranosyl-21,22-O-diangeloyl-3beta,16 alpha,21 beta,22 alpha,28-pentahydroxyolean-12-ene (28), R(1)-barrigenol (29), scopolin (30), and 5-methoxyscopolin (31). The structures of these compounds were elucidated by spectroscopic and chemical analyses. Compounds 14-22 and 26-28 were tested in vitro for their activity against 59 cell lines from nine different human cancers including leukemia, non-small cell lung, colon, CNS, melanoma, ovarian, renal, prostate, and breast. It was found that compounds with two-acyl groups at C-21 and C-22 had cytotoxic activity for all cell lines tested with GI(50) 0.175-8.71 microM, while compounds without acyl groups at C-21 and C-22 had weak or no cytotoxic activity. These results suggest that the acyl groups at C-21 and C-22 are essential for their activity.     

Biosynthesis of a neo-epi-verrucosane diterpene in the liverwort Fossombronia alaskana. A retrobiosynthetic NMR study

The biosynthesis of the diterpene 8alpha-acetoxy-13alpha-hydroxy-5-oxo-13-epi- neoverrucosane in the arctic liverwort Fossombronia alaskana was studied by incorporation experiments using [1-(13)C]- and [U-(13)C(6)]glucose as precursors. The (13)C-labeling patterns of acetyl-CoA, pyruvate, and phosphoenolpyruvate in intermediary metabolism were reconstructed from the (13)C NMR data of biosynthetic amino acids (leucine, alanine, phenylalanine) and were used to predict hypothetical labeling patterns for isopentenyl pyrophosphate formed via the mevalonate pathway and the deoxyxylulose pathway. The labeling patterns observed for the neoverrucosane diterpene were consistent with the intermediate formation of geranyllinaloyl pyrophosphate assembled from dimethylallyl pyrophosphate and three molecules of isopentenyl pyrophosphate generated predominantly or entirely via 1-deoxyxylulose 5-phosphate. The experimental data can be integrated into a detailed biosynthetic scheme involving a 1,5-hydride shift. The postulated involvement of the 1,5-hydride shift was confirmed by an incorporation experiment with [6,6-(2)H(2)]glucose.     

The orientation of substrate and reaction intermediates in the active site of ribulose-1,5-bisphosphate carboxylase

There are four possible orientations of the substrate ribulose 1,5-bisphosphate in the active site of ribulose-1,5-bisphosphate carboxylase. Distinction between these four possible orientations has been made on the basis of 31P NMR and borohydride-trapping experiments. The orientation of the reaction-intermediate analog, 2'-carboxy-D-arabinitol 1,5-bisphosphate with respect to the divalent metal ion was determined by 31P NMR studies of the quaternary complex, enzyme.CO2.Ni2+.2'-carboxyarabinitol 1,5-bisphosphate. Assignment of the phosphorus resonances of this complex was made by labeling the phosphoryl group at either C-1 or C-5 with 17O. The phosphorus atom closer to the paramagnetic metal ion, Ni2+, to which the broader of the phosphorus resonances is attributed, has been identified as that attached to C-1. When bound to the active site of carbaminated enzyme, D-ribulose 1,5-bisphosphate was reduced by sodium borohydride with absolute stereospecificity to D-arabinitol 1,5-bisphosphate. The reduction of the enzyme-bound substrate thus occurred on the Si face of the C-2 carbonyl group. These two results together establish that ribulose 1,5-bisphosphate is oriented within the active site so that 1) the phosphoryl group at C-1 is closer to the divalent metal ion than that at C-5 and 2) the Si face of the carbonyl group points to the "outside world."     

Amyloid fibril formation by A beta 16-22, a seven-residue fragment of the Alzheimer's beta-amyloid peptide, and structural characterization by solid state NMR

The seven-residue peptide N-acetyl-Lys-Leu-Val-Phe-Phe-Ala-Glu-NH(2), called A beta(16-22) and representing residues 16-22 of the full-length beta-amyloid peptide associated with Alzheimer's disease, is shown by electron microscopy to form highly ordered fibrils upon incubation of aqueous solutions. X-ray powder diffraction and optical birefringence measurements confirm that these are amyloid fibrils. The peptide conformation and supramolecular organization in A beta(16-22) fibrils are investigated by solid state (13)C NMR measurements. Two-dimensional magic-angle spinning (2D MAS) exchange and constant-time double-quantum-filtered dipolar recoupling (CTDQFD) measurements indicate a beta-strand conformation of the peptide backbone at the central phenylalanine. One-dimensional and two-dimensional spectra of selectively and uniformly labeled samples exhibit (13)C NMR line widths of <2 ppm, demonstrating that the peptide, including amino acid side chains, has a well-ordered conformation in the fibrils. Two-dimensional (13)C-(13)C chemical shift correlation spectroscopy permits a nearly complete assignment of backbone and side chain (13)C NMR signals and indicates that the beta-strand conformation extends across the entire hydrophobic segment from Leu17 through Ala21. (13)C multiple-quantum (MQ) NMR and (13)C/(15)N rotational echo double-resonance (REDOR) measurements indicate an antiparallel organization of beta-sheets in the A beta(16-22) fibrils. These results suggest that the degree of structural order at the molecular level in amyloid fibrils can approach that in peptide or protein crystals, suggest how the supramolecular organization of beta-sheets in amyloid fibrils can be dependent on the peptide sequence, and illustrate the utility of solid state NMR measurements as probes of the molecular structure of amyloid fibrils. A beta(16-22) is among the shortest fibril-forming fragments of full-length beta-amyloid reported to date, and hence serves as a useful model system for physical studies of amyloid fibril formation.     

Heteroannelated and 7-deoxygenated goniofufurone mimics with antitumour activity: Design,synthesis and preliminary SAR studies

Cytotoxic (+)-goniofufurone mimic such as benzoxepane 2 was preferentially formed after the treatment of 7-O-benzoyl-5-O-benzyl (+)-goniofufurone derivative 6 with titanium(IV) fluoride. However, the corresponding 7-epimer 5 (derivative of 7-epi-goniofufurone) under the similar reaction conditions gave mainly 7-deoxy derivative 7 as a result of an unexpected 1,5-hydride shift. Extension of this methodology to the enantiomer ent-6 provided cytotoxic (?)-goniofufurone mimics ent-2 and ent-7. Synthesized compounds showed diverse growth inhibitory effects against selected tumour cell lines, but were devoid of any significant toxicity towards the normal foetal lung fibroblasts (MRC-5). A SAR study reveals the structural features of these lactones that are beneficial for their antiproliferative activity, such as presence of an additional oxepane ring, the absolute stereochemistry and the presence of a deoxy function at the C-7 position.     

New polyoxygenated steroids from the Antarctic octocoral Dasystenella acanthina

The chemical study of the Antarctic octocoral Dasystenella acanthina has led to the isolation of the new polyoxygenated steroids (24R,22E)-24-hydroxycholest-4,22-dien-3-one (1), 23-acetoxy-24,25-epoxycholest-4-en-3-one (2), 12beta-acetoxycholest-4-en-3,24-dione (3), 12beta-acetoxy-24,25-epoxycholest-4-en-3-one (4), (22E)-25-hydroxy-24-norcholest-4,22-dien-3-one (5), 3alpha-acetoxy-25-hydroxycholest-4-en-6-one (6), and 3alpha,11alpha-diacetoxy-25-hydroxycholest-4-en-6-one (7), whose structures have been established by spectroscopic analysis. The absolute stereochemistry at C-24 in compound 1 has been determined through the 1H NMR study of the corresponding (R)- and (S)-MPA esters. All the new compounds showed significant activities as growth inhibitors of several human tumor cell lines. In addition, cytostatic and cytotoxic effects were also observed on selected tumor cell lines.     

Signal assignments and chemical-shift structural analysis of uniformly 13C, 15N-labeled peptide, mastoparan-X, by multidimensional solid-state NMR under magic-angle spinning

Carbon-13 and nitrogen-15 signals of fully isotope-labeled 15-residue peptide, glycinated mastoparan-X, in a solid state were assigned by two- and three-dimensional NMR experiments under magic-angle spinning conditions. Intra-residue spin connectivities were obtained with multidimensional correlation experiments for C'-C(alpha)-C(beta) and N-C(alpha)-C(beta). Sequence specific assignments were performed with inter-residue C(alpha)-C(alpha) and N-C(alpha)C(beta) correlation experiments. Pulse sequences for these experiments have mixing periods under recoupled zero- and double-quantum (13)C-(13)C and (15)N-(13)C dipolar interactions. These correlation spectra allowed the complete assignments of (13)C and (15)N backbone and (13)C(beta) signals. Chemical shift analysis of the (13)C and (15)N signals based on empirical and quantum chemical databases for proteins indicated that the backbone between residues 3 and 14 forms alpha-helix and residue 2 has extended conformation in the solid state. This structure was compared with the G-protein- and membrane-bound structures of mastoparan-X.