Rubescins F–H, new vilasinin-type limonoids from the leaves of Trichilia rubescens (Meliaceae)

2019 ◽  
Vol 74 (7-8) ◽  
pp. 175-182
Author(s):  
Armelle Tontsa Tsamo ◽  
Julio Issah Mawouma Pagna ◽  
Pamela Kemda Nangmo ◽  
Pierre Mkounga ◽  
Hartmut Laatsch ◽  
...  
Keyword(s):  
Ab Initio ◽  
Methylene Chloride ◽  
High Resolution Mass Spectrometry ◽  
Optical Rotation ◽  
Cyclopropane Ring ◽  
Dispersion Data ◽  
Rotation Dispersion ◽  
Oxetane Ring ◽  
Related Compounds ◽  
Potential Precursor

Abstract Three new limonoids, designated as rubescins F (1), G (2), and H (3), together with two known compounds of this type, TS1 (4) and trichirubine A (5), were isolated from methylene chloride/methanol extracts of Trichilia rubescens leaves. The structures of these compounds were elucidated based on 1D and 2D nuclear magnetic resonance (NMR) analysis and complemented by electrospray ionization high-resolution mass spectrometry results and by comparison to data of related compounds described in the literature and ab initio calculations. Rubescin F (1) is the first limonoid from Trichilia spp. with an oxetane ring between C-7 and C-14, which seems to be formed by the isomerization of TS1 (4). The γ-hydroxybutenolide rubescin G (2) is a potential precursor of trichirubine A (5), whereas rubescin H (3) is the first example of a triterpenoid with a single bond between C-7/C-14, forming a cyclopropane ring. The absolute configuration of these limonoids was derived from biosynthetic considerations and ab initio calculations of NMR and optical rotation dispersion data.

scholarly journals OPTICAL ROTATION AND HELICAL POLYPEPTIDE CHAIN CONFIGURATION IN COLLAGEN AND GELATIN

1955 ◽  
Vol 1 (3) ◽  
pp. 203-214 ◽  
Author(s):  
Carolyn Cohen
Keyword(s):  
Optical Activity ◽  
Optical Rotation ◽  
Specific Rotation ◽  
X Ray Diffraction ◽  
Citrate Buffer ◽  
Gelatin Films ◽  
Dispersion Data ◽  
Single Term ◽  
Native Collagen ◽  
Helical Configuration

The optical rotation phenomena exhibited by a citrate-extracted fraction of ichthyocol (from carp swim bladder), as well as by the parent gelatin derived therefrom, have been studied. Dispersion data for all cases follow a single-term Drude equation, but the variations with state are adequately expressed by simple reference to changes in [α]D as follows:— 1. The native collagen fraction, dispersed in 0.15 M citrate buffer at pH 3.7 in the cold (11°C.), yields a high negative specific rotation, [α]D, near –350°. 2. During equilibration at 40°C., which causes conversion to a monodisperse parent gelatin, the rotation drops to about –110°. 3. Gelation at 2°C. results in a partial regain of rotation to around –290°. This mutarotation is reversible, depending on temperature. 4. In the range 0.02 to 0.28 per cent the native ichthyocol and the warm gelatin solutions show little concentration dependence, but with the cold gelatin solutions the specific rotation increases with concentration. Gelatin films formed by cold evaporation yield high specific rotation (ca. –620°), but those formed by hot evaporation retain low optical activity. 5. Since this same collagen-gelatin system has been investigated physicochemically, it is possible to relate molecular changes to the observed variations in optical rotation. Conclusions are similar to those of Robinson (1953), who studied other gelatins: high negative rotation is believed related to a native collagen polypeptide configuration, herein specified as helical (from x-ray diffraction considerations) and destroyed by heating. The possible roles of intermolecular interactions and of prevalent pyrrolidine constituents in influencing the helical configuration and optical activity are discussed.

scholarly journals Nucleic Acid Related Compounds. 8. Direct Conversion of 2′-Deoxyinosine to 6-Chloropurine 2′-Deoxyriboside and Selected 6-Substituted Deoxynucleosides and Their Evaluation As Substrates of Adenosine Deaminase

1973 ◽  
Vol 51 (19) ◽  
pp. 3161-3169 ◽  
Author(s):  
Morris J. Robins ◽  
Gerald L. Basom
Keyword(s):  
Adenosine Deaminase ◽  
Methylene Chloride ◽  
Potassium Fluoride ◽  
Direct Conversion ◽  
Chloride Complex ◽  
High Yield ◽  
Mass Spectral ◽  
Quaternary Ammonium Chloride ◽  
Related Compounds

Trifluoroacetylation of 2′-deoxyinosine (2), obtained by enzymatic deamination of 2′-deoxyadenosine (1), gave the 3′,5′-bis-O-trifluoroacetate (3). Reaction of the electronegatively substituted deoxynucleoside, 3, with DMF-thionyl chloride complex in refluxing methylene chloride gave a high yield of 6-chloropurine 2′-deoxyriboside (4) after deblocking.Displacement of chloride of 4 by hydrosulfide to give 6-mercaptopurine 2′-deoxyriboside (5) followed by sulfur alkylation with p-nitrobenzyl bromide gave 6-S-(p-nitrobenzyl) thiopurine 2′-deoxyriboside (6) which was alternatively prepared by displacement of chloride from 4 by p-nitrobenzyl mercaptide, generated in situ from the isothiouronium salt. Methyl mercaptide reaction with 4 gave 6-methylthiopurine 2′-deoxyriboside (7). Treatment of 4 with trimethylamine gave the corresponding quaternary ammonium chloride (8) which was allowed to react with potassium fluoride to give 6-fluoropurine 2′-deoxyriboside (9). Respective amine displacements on 4 gave 6-benzylaminopurine 2'-deoxyriboside (10), and 6-hydroxylaminopurine 2′-deoxyriboside (11). Reaction of 4 with liquid ammonia completed the first reported transformation of 2′-deoxyinosine (2) to 2′-deoxyadenosine (1).Biological rationale for the synthesis of these 2′-deoxynucleosides and their evaluation as substrates of adenosine deaminase are discussed. Major mass spectral fragmentations are tabulated.

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