Synthesis of naturally occurring phloroglucinol derivatives

Starting with isobutyryl phloroglucinol nine naturally occurring compounds from $\text{Helichrysum}$ species were synthesized.     

Synthesis and structural revision of naturally occurring ayapin derivatives

The synthesis of three highly oxygenated naturally occurring coumarins, 8-methoxy-6,7-methylenedioxycoumarin, 5-methoxy-6,7-methylenedioxycoumarin and 5,8-dimethoxy-6,7-methylenedioxycoumarin is described for the first time, together with a new method for the preparation of ayapin (6,7-methylenedioxycoumarin). Comparison of the spectroscopic data of the synthetic tetraoxygenated coumarin 5,8-dimethoxy-6,7-methylenedioxycoumarin with literature reports resulted in the structural revision of several natural coumarins. Two coumarins, both identified as 5,8-dimethoxy-6,7-methylenedioxycoumarin must have other structures, while the structure of another coumarin, described as the isomeric 7,8-dimethoxy-5,6-methylenedioxycoumarin has to be revised to 5,8-dimethoxy-6,7-methylenedioxycoumarin.     

Synthesis of some naturally occurring prenylated juglone derivatives

Synthesis of -caryopterone (I), -dihydrocaryopterone )II), 9-methoxy--lapachone (III) and 4,9-dihydroxy--lapachone (IV) has been carried out starting from juglone via 2,8-dihydroxy-1,4-naphthoquinone.     

Separation ofcis andtrans isomers of naturally occurring hydroxycinnamic acids by high-pressure liquid chromatography

Summary The separation of hydroxycinnamic acids has been investigated by high-pressure liquid chromatography using a micro C₁₈ bonded phase. Irradiation oftrans-ferulic and sinapic acids readily gave a mixture ofcis-trans isomers which can be also separated with the system described.     

Mass spectra of trimethylsilyl derivatives of naturally occurring flavonoid aglycones and chalcones

Electron impact mass spectra of the trimethylsilyl derivatives of a series of flavonoid aglycones and chalcones are reported. The spectra show prominent ions arising from fragmentation of the trimethylsilyl (TMS) groups. Inter-actions between adjacent TMS groups, and between TMS groups in the 3- or 5-position (6′-position for the chalcones) and the C-ring carbonyl, yield structurally significant ions. Few fragments associated with the retro-Diels-Alder cleavage of the C-ring characteristic of the underivatized compounds, are observed. The TMS derivatives thus provide complementary information for the identification of flavonoid aglycones and chalcones in biological systems.     

Mass spectra of some naturally occurring stictane triterpenoids and their trimethylsilyl derivatives

The mass spectra of ten di- and tri-oxygenated stictane triterpenoids and their trimethylsilyl derivatives have been studied in detail. Gas chromatography mass spectrometry of the TMS derivatives on OV-17 and OV-101 columns provided useful separations and identifications of mixtures of stictanes triterpenoids in lichen extracts. The major fragmentations involve ring C, but specific cleavages in rings A, B and E are also observed which allow the substitution pattern of the skeleton to be readily determined. The formation of an intense [M – C₅H₁₁?]⁺ ion for 22α-OTMS stictanes appears specific to their ring E configuration.     

Cannabispirone and cannabispirenone,two naturally occurring spiro-compounds

Structure elucidation of two naturally occurring acidic compounds from Cannabis gave two spiro-compounds. The spectroscopic properties (¹H-NMR, ¹³C-NMR, MS, IR and UV) and interpretation of these spectra are given.     

Conformational isomers in the photocyclodimerization of N-acylated dibenz[b,f]azepine derivatives

The benzophenone-sensitised photodimerizations of N-acetyl- and N-propionyldibenz[e,f]azepine were investigated in acetone as the solvent. In both the systems, the ¹H NMR analysis of the products revealed two isomeric photodimers differing in the chemical shifts and coupling constants of the cyclobutane protons, aromatic protons and the protons of the acetyl or propionyl group. Upon raising the temperature to ca. 70 °C the signals merge. The findings can be ascribed to a single thermally restricted conformational process such as the rotation about the C–N amide bond. The process exhibits free activation energies: ΔG^#=(74±2) kJ mol⁻¹ (N-acetyl) and ΔG^#=(70±2) kJ mol⁻¹ (N-propionyl).     

Synthesis of naturally occurring polyynes

Over the past fifty years, hundreds of polyyne compounds have been isolated from nature. These often unstable molecules are found in sources as common as garden vegetables and as obscure as bacterial cultures. Naturally occurring polyynes feature a wide range of structural diversity and display an equally broad array of biological properties. Early synthetic efforts relied primarily on Cu-catalyzed, oxidative acetylenic homo- and heterocoupling reactions to assemble the polyyne framework. The past 25 years, however, have witnessed a renaissance in the field of polyyne natural product synthesis: transition-metal-catalyzed alkynylation reactions and asymmetric transformations have combined to substantially expand access to natural polyynes. This Review recounts these synthetic achievements and also highlights both the natural source(s) and biological relevance for many of these compounds.     

A novel strategy for the preparation of naturally occurring phosphocitrate and its partially esterified derivatives

A novel method for the synthesis of phosphocitrate (1, PC) starting from triethyl ester of citric acid and MeOPCl2 is described. The method is based on selective stepwise hydrolysis of ester moieties from the intermediate Me-O-P(O)(Cl)(Z) (Z = triethylcitrate), 4a, which also allows one to prepare partially esterified derivatives of PC with good yield and purity without chromatographic purifications.     

Tetrahydroberberine,a pharmacologically active naturally occurring alkaloid

Tetrahydroberberine (systematic name: 9,10‐dimethoxy‐5,8,13,13a‐tetrahydro‐6H‐benzo[g][1,3]benzodioxolo[5,6‐a]quinolizine), C₂₀H₂₁NO₄, a widely distributed naturally occurring alkaloid, has been crystallized as a racemic mixture about an inversion center. A bent conformation of the molecule is observed, with an angle of 24.72 (5)° between the arene rings at the two ends of the reduced quinolizinium core. The intermolecular hydrogen bonds that play an apparent role in crystal packing are 1,3‐benzodioxole –CH₂...OCH₃ and –OCH₃...OCH₃ interactions between neighboring molecules.     

The synthesis of carboxymethyl derivatives of purines and pyrimidines and their condensation with naturally occurring macromolecules

1-Carboxymethylthymine, 1-carboxymethylcytosine and 9-carboxymethyladenine were obtained by the direct carboxymethylation of the appropriate bases. In addition a small amount of 3-carboxymethyladenine was obtained. 9-Carboxymethylhypoxanthine was obtained by deamination of 9-carboxymethyladenine. 1-Carboxymethyluracil, 1-carboxymethylthymine and 9-carboxymethyl-hypoxanthine were each condensed with protamine and with dextran to give water-soluble, base-substituted polymers. The 1-carboxymethylthymine-dextran showed a slow decrease in optical density at 268 nm in 2 × SSC at 20°, of 30%. This did not occur in 7M urea. 1-Carboxymethylthymine-dextran gave an additional hypochromic effect with polyadenylic acid in 2 × SSC at 4° or 14° of 13% and 9% respectively. The ratio of thymine: adenine residues at the point of maximum hypochromicity was 3:1. The other dextran derivatives did not show similar hypochromic effects. The 1-carboxy-methylthymine-protamine gave a precipitate with polyadenylic acid probably due to electrostatic interaction.     

Conformational studies by dynamic NMR. 86. Structure, stereodynamics, and cryogenic enantioseparation of the stereolabile isomers of o-dinaphthylphenyl derivatives

Static and dynamic stereochemistry of the hydrocarbon comprising a phenyl ring bearing two alpha-naphthyl substituents in the ortho positions, i.e., 1,2-di-(4-methyl-naphth-1-yl)-benzene 1, has been studied by a combination of variable temperature NMR, cryogenic HPLC, and MM calculations. Whereas in solution both syn (meso) and anti (chiral) forms were observed and the corresponding interconversion barrier was determined (Delta G(++) = 19.5 kcal mol(-1)), only the diastereoisomer anti was found to be present in the crystalline state (X-ray diffraction). When the molecule is rendered asymmetric by introduction of a nitro group in the phenyl ring as in 1,2-di-(4-methyl-naphth-1-yl)-4-nitrobenzene 2, the chiral syn and anti diastereoisomers are simultaneously present both in solution and in the solid state, albeit in different proportions. Cryogenic chromatography on a HPLC chiral stationary phase at 20 degrees C allowed the stereolabile diastereoisomers and the corresponding enantiomers to be separated.