Mass spectrometry of sesquiterpenoids of the carotane series. Influence of various methods of ionization on the fragmentation of sesquiterpenols

The mass spectra of five natural sesquiterpenols with various methods of ionization have been studied. A distinct direction of breakdown according to the alternative positions of the OH group at the C-4 or C-5 atom for the skeleton has been found. It has been established that the use of chemical ionization and of secondary-ion mass spectrometry raises the intensity of the molecular ions and increases specific directions of fragmentation. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 522–525, July–August, 1993.     

Negative Ion CID Fragmentation of <Emphasis Type="Italic">O-</Emphasis>linked Oligosaccharide Aldoses—Charge Induced and Charge Remote Fragmentation

Collision induced dissociation (CID) fragmentation was compared between reducing and reduced sulfated, sialylated, and neutral O-linked oligosaccharides. It was found that fragmentation of the [M – H]^– ions of aldoses with acidic residues gave unique Z-fragmentation of the reducing end GalNAc containing the acidic C-6 branch, where the entire C-3 branch was lost. This fragmentation pathway, which is not seen in the alditols, showed that the process involved charge remote fragmentation catalyzed by a reducing end acidic anomeric proton. With structures containing sialic acid on both the C-3 and C-6 branch, the [M – H]^– ions were dominated by the loss of sialic acid. This fragmentation pathway was also pronounced in the [M – 2H]^2– ions revealing both the C-6 Z-fragment plus its complementary C-3 C-fragment in addition to glycosidic and cross ring fragmentation. This generation of the Z/C-fragment pairs from GalNAc showed that the charges were not participating in their generation. Fragmentation of neutral aldoses showed pronounced Z-fragmentation believed to be generated by proton migration from the C-6 branch to the negatively charged GalNAc residue followed by charge remote fragmentation similar to the acidic oligosaccharides. In addition, A-type fragments generated by charge induced fragmentation of neutral oligosaccharides were observed when the charge migrated from C-1 of the GalNAc to the GlcNAc residue followed by rearrangement to accommodate the ^0,2A-fragmentation. LC-MS also showed that O-linked aldoses existed as interchangeable α/β pyranose anomers, in addition to a third isomer (25% of the total free aldose) believed to be the furanose form.     

Mass spectra of pseudoguaianolides related to carpesiolin

The main directions of fragmentation and the EI of six pseudoguaianolides related to carpesiolin have been studied. It has been established that acylation of the OH group at C-6 suppresses the selective breakdown of the guaiane skeleton, while the simultaneous presence of AcO groups at C-2 and C-4 favors the formation of a number of characteristic ions. The hydrogenation of the exomethylene group has no appreciable influence on direction of fragmentation.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 530–535, July–August, 1993.     

Cyclization of cembrane diterpenoids. V. Selectivity of the formation of a product of the cyclization of cembrene under the action of N-bromosuccinimide,and the crystal structure of this product

Under the action of N-bromosuccinimide in aqueous acetone, cembrene has given a low yield of a cyclization product, the structure and stereochemistry of the molecule of which have been established by x-ray structural analysis. In contrast to the cyclization of cembrene under the action of formic acid, in the reaction under consideration a 1,5-hydride shift in the last stage dominates substantially over the splitting out of a proton from the methyl group at C-4. Novosibirsk Institute of Organic Chemistry, Siberian Division of the Russian Academy of Sciences. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 687–691, September–October, 1993.     

Formation of intermolecular hydrogen bonds in light-sensitive crystals of C-2′-(o-oxyphenyl)vinyl-N-p-methylphenyl nitrone,C-2′-(2″-oxy-5″-bromophenyl)vinyl-N-p-methylphenyl nitrone,C-2′-(2″-oxy-5″-bromophenyl)-vinyl-N-phenyl nitrone,and C-2′-(o-oxyphenyl)vinyl-n-methyl nitrone

This paper studies the crystal structure of new substituted light-sensitive azomethine N-oxides (nitrones): C-2′-(o-oxyphenyl)vinyl-N-p-methylphenyl nitrone (1), C-2′-(2″-oxy-5″-bromophenyl)vinyl-N-p-methylphenyl nitrone (2), C-2′-(2″-oxy-5″-bromophenyl)-vinyl-N-phenyl nitrone (3), and C-2′-(o-oxyphenyl)vinyl-N-methyl nitrone (4). In contrast to the compounds studied earlier [1, 2], C-2′-(β-oxy-α-naphthyl)vinyl-N-p-methylphenyl nitrone (5), C-2′-(β-oxy-α-naphthyl)vinyl-N-phenyl nitrone (6), C-2′-(o-oxyphenyl) vinyl-N-phenyl nitrone (7), and C-2′-(o-oxyphenyl)vinyl-N-p-bromophenyl nitrone (8), the nitrones studies in this work have anti-rather than syn-orientations of the nitrone and hydroxyl groups. Due to this spatial arrangement of the proton-donating hydroxyl and proton-accepting nitrone groups, molecules in crystals 1–4 are bonded by intermolecular hydrogen bonds (IHB) to form chains but not centrosymmetric dimeric associates (CDA). Two types of chain arrangements were revealed: “head-to-tail” and “head-to-tail, tail-to-head”. It is shown that the introduction of an alkyl substituent instead of an aryl one at the nitrogen atom of the nitrone group in 4 leads to a change in the geometry of the IHB in the H-associate. It is proven that the hydroxyl proton can undergo an intermolecular O→O transfer in the chain of hydrogen bonds in crystals 1–4, which can give rise to photochemical transformations in these crystals. Institute of Chemical Physics in Chernogolovka, Russian Academy of Sciences. Translated fromZhurnal Strukturnoi Khimii, Vol. 37, No. 2, pp. 349–362, March–April, 1996. Translated by L. Smolina     

Investigation of the conformational transformations in some 7α-methyl-6-oxa-14β-analogs of steroidal estrogens by NMR spectroscopy

The stereochemical structure and conformational transformations of two 6-oxa-14β-estra-1,3,5(10), 8(9)-tetraenes having an α-methyl group at position 7 were investigated. It was found that the substituent at the C-17 atom has an effect on the formation of the conformers in solution. In the analog containing a C-17 keto group in solution there are two conformers, whereas the 17α-acetoxy derivative has only one conformer. In memory of Prof. A. A. Potekhin. __________ Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 6, pp. 82–834, June, 2008.     

Use of broadened13C NMR signals in complexes of nucleosides with Mn(II) to evaluate the conformational equilibrium of the ribose ring

The¹³C NMR spectra of chelate complexes of nucleosides with Mn(II) under fast-exchange conditions have been studied. It has been established that the state of the conformational equilibrium of the ribose ring within the framework of the two-sided exchange 2′-endo (S) ⇆ 3′-endo (N) can easily be evaluated from the broadening of the C-1′ and C-4′ signals. The results obtained by the broadening method agree well with those of methods used previously. All-Union Scientific-Research Institute of Applied Biochemistry, Olaine. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 678–680, September–October, 1980.     

Mass spectrometry of sesquiterpenoids of the carotane series. Influence of various methods of ionization on the fragmentation of sesquiterpenols

The mass spectra of five natural sesquiterpenols with various methods of ionization have been studied. A distinct direction of breakdown according to the alternative positions of the OH group at the C-4 or C-5 atom for the skeleton has been found. It has been established that the use of chemical ionization and of secondary-ion mass spectrometry raises the intensity of the molecular ions and increases specific directions of fragmentation.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Republic of Uzbekistan, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 522–525, July–August, 1993.     

Study on fragmentation behavior of 5/7/6-type taxoids by tandem mass spectrometry

The mass spectrometric behaviors of seven compounds, namely four 4beta(20),5-oxetane 5/7/6-type taxoids (i.e. taxayuntin A, taxayuntin B, taxayuntin and taxayuntin C) and three 4(20)-methylene 5/7/6-type taxoids (i.e. brevifoliol, taxchinin A and 7-acetyl-10-deacetyl-7-debenzoylbrevifoliol) have been investigated by the positive ion FAB-MS/MS technique. The fragmentation has been correlated with the types and positions of substituents of these compounds. It has been found that with the OH group at the C-10 position, taxayuntin A, taxayuntin B and 7-acetyl-10-deacetyl-7-debenzoylbrevifoliol are dominated by the loss of H2O, while with the BzO group at the C-10 position, taxayuntin, taxayuntin C, brevifoliol and taxchinin A preferentially eliminate the BzO group. In addition, C-2 is an active site, and neutral loss from the C-2 position readily occurs. The four 4beta(20),5-oxetane 5/7/6-type taxoids produce the terminal product ion with a stable conjugated system at m/z 311, while the 4(20)-methylene 5/7/6-type taxoids brevifoliol and 7-acetyl-10-deacetyl-7-debenzoylbrevifoliol produce this ion at m/z 237, and taxchinin A at m/z 253. Interestingly, characteristic fragment ions involving the loss of a 118 u group were observed for taxayuntin, and a possible fragmentation mechanism is given. The major fragmentation pathways and mechanisms of ion formation for the compounds are proposed on the basis of CID spectra and accurate mass measurements. The results of this paper will be helpful for structural analysis of analogs.     

Mass spectra of artabin,hanphyllin, and solonitolide

The processes of fragmentation of the germacranolides artabin, hanphyllin, and solonitolide have been considered from the points of view of various methods of migration of the π-bonds of the ten-membered macrocycle, such as the retrodiene reaction, and the MacLafferty and Cope rearrangements. The occurrence of a thermal rearrangement has been detected for artabin. The influence of the additional OH group in the solonitolide molecule on the nature of its fragmentation is discussed. Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 636–643. September–October, 1980.     

Mass spectra of substituted Δ2-1,2,4-oxadiazolines—I

The electron impact fragmentation of four Δ²-1,2,4-oxadiazolines with substituents at positions 3 and 5 has been examined. The direct analysis of daughter ions and high resolution mass measurements provided valuable information regarding certain ions. The present study clearly demonstrates that the substitution of phenyl or a substituted phenyl group for alkyl at C-3 and alkyl in place of a phenyl substituent at C-5 in the oxadiazoline system alters the fragmentation modes considerably.     

Glycosylation of triterpenoids of the dammarane series. X. Regio- and stereoselective synthesis of 20(S)-protopanaxadiol 3-O-β-D-glucopyranoside (ginsenoside Rh2)

The regio- and stereoselective synthesis of ginsenoside R_h2, which possesses antitumoral activity, has been effected by the glycosylation of 12β-acetoxydammar-24-ene-3β,20(S)-diol. Condensation with α-acetobromoglucose was carried out in the presence of silver oxide in dichloroethane at room temperature, and the yield of the desired glycoside amounted to 50%. A method for the selective protection of the C-12-OH group of dammar-24-ene-3β,12β,20(S)-triol [20(S)-protopanaxadiol] has been proposed. Pacific Ocean Institute of Bioorganic Chemistry, Far Eastern Branch, USSR Academy of Sciences, Vladivostok. Translated from Khimiya Prirodnykh Soedinenii, Vol. 6, pp. 813–816, November–December, 1989.     

Stereochemistry of guaianolides ofFerula oopoda

The stereochemistries of badkhyzin, isobadkhyzin, ferulidin, and ferulin, guaianolides fromFerula oopoda (Boiss. et Buhse) Boiss. have been established. The stereochemistries of badkhyzin and of 8-hydroxyachillin (at C-5, C-6, C-7, C-8, C-11) are identical. When the lactone ring is opened with alkalis, badkhyzin isomerizes only at the C-6 center. V. L. Komarov Institute of Botany, Academy of Sciences of the Azerbaidzhan SSR, Baku. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 629–633, September–October, 1980.     

The mass spectra of some C-19 modified cholesteryl derivatives

The mass spectra of twenty one C-19 modified cholesteryl derivatives have been determined and compared with results for related systems. In the case when the hydrogen(s) of the C-19 group have been replaced by other groups the metastable evidence shows that in those molecules with a C-3 hydroxyl group the loss of water followed by the loss of the C-19 group gives rise to an intense ion at m/e 353, whereas the loss of the C-19 group with hydrogen transfer to the ion, followed by the loss of water gives rise to the large ion at m/e 354. In contrast in the case of the C-3 acetates the main fragmentation is the loss of acetic acid followed by the loss of the C-19 group to give the ion at m/e 353. This is rationalised on the basis of results observed in other systems. In the case of the C-3 tosylates evidence for pyrolysis before electron impact fragmentation is presented. The subsequent fragmentation of the large ions at m/e 354, 353 and other m/e values in the high mass region is shown to be in line with earlier work.     

phosphate hydrate complexes of singly and doubly charged magnesium ions: Structure,energies, and spin states

For mixed magnesium phosphate hydrate complexes containing Mg²⁺ and Mg⁺ cations and HPO₄²⁻, HPO₄⁻, and H₂P₂O₇²⁻ anions, theoretical analysis of the electronic structure and energies has been performed at the model level in order to predict the actual role of these systems in various reactions that occur in the catalytic sites of ATP synthesizing enzymes. The calculations (DFT/B3LYP, MP2 with the 6–31G* basis set) of isolated aqua complexes Mg(H₂O) _n ^p (n = 1−6, p = 0, +1, +2) show that their relative stability monotonically increases with increasing n in each series and sharply decreases at a given n in going from the charged systems of Mg²⁺ (4–16 eV) and Mg⁺ (2–7 eV) to the neutral systems of Mg (<2 eV). An even higher stability is predicted for mixed magnesium complexes. The energies of fragmentation of mixed Mg²⁺ complexes into singlet phosphate and Mg²⁺-containing fragments at n = 0–4 are within 6–27 eV, and the energies of fragmentation into the corresponding radical ions are within 3–10 eV; for the Mg⁺ complexes, the fragmentation energies are also high (6–14 eV). The reasons for the enhanced stability of the complexes of both types have been analyzed with allowance for the predicted specific features of the electron density redistribution upon complex formation. Typical changes in the geometry of the P- and Mg-containing fragments caused by formation of mixed complexes have been discussed in the framework of the vibronic model of heteroligand systems. The high stability of all mixed magnesium complexes relative to various fragmentation products presumably rules out any dissociative processes in them in the course of ATP synthesis with the participation of phosphorylating enzymes.     

13C NMR spectra of biologically active compounds. VIII. Stereochemistry of a triterpeneglycoside — Glycyrrhizic acid — And its derivatives

Details of the¹³C NMR spectra of glycyrrhizic acid and four of its derivatives are given, and on their basis the configurations of the anomeric centers of the carbohydrate chain have been redetermined and the β-configuration of the C-1′ carbon atom has been suggested. Institute of Chemistry, Bashkir Scientific Center, Urals Branch, USSR Academy of Sciences, Ufa. Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 500–505, July–August, 1989.     

Etude en Basse Tension de l'Androstane Dione-3,17—Application a la Localisation du Deuterium

The fragmentation mechanisms of (5α) 3,17-androstanedione have been studied in order to determine whether the deuterium is located at C-4 or C-6. This is possible at low voltage where a peak at m/e 216, arising from a A-ring cleavage allows the determination of isotope distribution between C-4 and C-6.     

Selective reduction of 1,4-diarylimidazoline-3-oxides to imidazolidin-1-ols and hydroxylamine derivatives

Abstract  

C-2-unsubstituted imidazoline-3-oxides were reduced with NaBH₄ in THF to give the corresponding trans-3,5-diarylimidazolidin-1-ols, while under the same conditions C-2-substituted derivatives gave the corresponding ring–chain–ring tautomers. Treatment of the crude reaction mixture from the reduction of C-2-unsubstituted imidazoline-3-oxides with a MeOH–H₂O mixture provided reductive C–N bond cleavage to give hydroxylamines, while under the same conditions ring–chain–ring tautomers remained unchanged.     

Synthesis of 2-aryl-6-methyl-5-nitroquinoline derivatives as potential prodrug systems for reductive activation

A range of novel 2-aryl-5-nitroquinolines have been synthesised as potential prodrug systems for bioreductive activation. Thus 5-nitroquinoline underwent vicarious nucleophilic substitution at C-6 with bromoform anion to give, after hydrolysis and reduction, the quinoline-6-methanol. Introduction of chlorine at C-2 was followed by palladium-catalysed Suzuki coupling to install the 2-aryl substituent. A fluorescent model ‘drug’, 7-hydroxy-4-methylcoumarin was coupled to the 6-hydroxymethyl group, and its fragmentation upon reduction of the nitro group was investigated.     

Aconityl-derived polymers for biomedical applications. Modeling study of cis–trans isomerisation

 Soluble polymers have been prepared that are designed to undergo enhanced rates of hydrolysis at pH values less than that observed in blood circulation. The degradable element in the polymer mainchain is derived from cis-aconityl acid and is defined by a carboxylic acid pendent functionality (C-4) that is cis across a double bond to an amide at C-1 in the polymer mainchain. While degradation studies in vitro have confirmed these polymers do undergo enhanced rates of degradation at acidic pH values, there is also increasing evidence that during the degradation process the double bond isomerises to the trans configuration and thus prevents the full degradation of a polymer. From a molecular modelling perspective we are seeking to understand the propensity for this cis–trans isomerisation and the mechanism of this cis–trans isomerisation is discussed. Received: 29 April 2002 / Accepted: 6 September 2002 / Published online: 14 February 2003