Ginkgolide

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Chemical structure of ginkgolides
Miraculous Ginkgolide B
ginkgolide
R1 R2 R3
A OH H H
B OH OH H
C OH OH OH
J OH H OH
M H OH OH
Structure of Gingkolide B

Ginkgolides are biologically active terpenic lactones present in Ginkgo biloba. They are diterpenoids with 20-carbon skeletons, which are biosynthesized from geranylgeranyl pyrophosphate.[1]

Ginkgolide B specifically, is a diterpenoid trilactone with six five-membered rings. It contains a spiro[4,4]-nonane carbocyclic ring, a tetrahydrofuran ring, and a very specific tert-butyl group at one of the rings (Figure 1). The class of ginkgolides was first isolated from the Ginkgo biloba tree in 1932.[2] The elucidation of its structure set in 1967 by Maruyama et al.[3] who isolated ginkgolide B in 1967.

Background[edit]

It is extracted from the root bark and leaves of the Ginkgo biloba (ginkyo meaning "silver apricot") tree found native in China. It is marketed to other countries that include Korea, France, the United States, etc. for the drug and clinical properties of the extracts. Present in the tree is less than 0.1 to 0.25% of ginkgolide B, the most abundant being ginkgolide A.[4]

Clinical Applications[edit]

This class of molecules have been researched for many years due to its ability to act as an anti-platelet-activating antagonist (PAF Receptor, Figure 2) in treating cardiovascular diseases.[2][5]

Ginkgolide B may be effective as preventive treatment in reducing migraine attack frequency.[6]

Ginkgolide B is also used in treatment for cerebrovascular disease. Research has also proven that ginkgolide B can also treat migraines in young ages[2][7][8] The literature indicates that ginkgolide B functions as a selective antagonist of glycine receptors based on noncompetitive inhibition for the neurological system that this compound performs.[5]

Spectroscopic studies for the elucidation of the individual structures for the ginkgolides[edit]

To determine ginkgolide B from the other ginkgolides, a crude mixture was separated in protocol[3] to receive a pure sample of the compound. From this, using refractive index and evaporation light-scattering detections as well as mass spectrometry determined its absolute structure. There are X-ray crystallography data and detailed NMR studies dealt on this molecule to emphasize that there is a hydroxyl group that points into the plane of the molecule. There are also the hydroxyls that are in plane with some of the lactone motifs, which creates intramolecular hydrogen bonds compared to ginkgolide A which doesn't. This characteristic is also be proved in spectral analysis.

Biosynthesis of Ginkgolide B[edit]

The biosynthesis of Ginkgolide B

While researchers have published chemical pathways to make this molecule, most of the designed syntheses were too complex and produced little of the actual material to run full analyses.[3] Therefore, studying the biosynthesis of the molecule is preferable.

Most of the natural product terpenoids start with isopentenyl diphosphate synthesized by the MEP pathway. This pathway also generates dimethylallyl diphosphate, from pyruvate and D-glyercaldehyde 3-phosphate (GAP). When coupled together, they form one molecule of geranylgeranyl diphosphate with geranylgeranyl diphosphate synthase.

A molecule of GGPP generates (1) (+)-copalyl in the presence of levopimaradiene synthase. (a) Then (1) loses its OPP group catalyzed by this same synthase, performing an intramolecular allylic cyclization with the two alkenes, to form (2) the sandaracopimarenyl cation. (b) This cation then undergoes an internal cyclization to stabilize the carbocation in the ring by proton transfer to form (3) intermediate. (c) By doing this, the molecule sets itself up for a methyl migration to stabilize that secondary cation and generate that tertiary carbocation at (4). (d) This induces a loss of proton to get (5) levopimaradiene. (e) With oxidation, a loss of a proton to form an aromatic ring generates (6) abietatriene. (g) This newly formed abietatriene undergoes a 1,2-alkyl shift to break the 6-membered ring into (7) with a five-membered ring (more favorable). (h) Another 1,2-alkyl shift takes place at the same time a ring cleavage takes place to generate (8). (i) Oxidation at all the positions with alkenes generates (9) intermediate which then undergoes ring closures featuring one hemiacetal and all three lactones to get ginkgolide B at (10).[9]

See also[edit]

References[edit]

  1. ^ Niels H. Andersen, Niels Johan Christensen, Peter R. Lassen, Teresa B.N. Freedman, Laurence A. Nafie, Kristian Strømgaard, Lars Hemmingsen (February 2010). "Structure and absolute configuration of ginkgolide B characterized by IR- and VCD spectroscopy". Chirality 22 (2): 217–223. doi:10.1002/chir.20730. 
  2. ^ a b c Stromgaard, K.; Nakanishi, K. "Chemistry and Biology of Terpene Trilactones from Ginkgo Biloba". Agnew. Chem. Int. Ed. (43): 1670–58. doi:10.1039/C19680001117. 
  3. ^ a b c Maruyama, M.; Terahara, A.; Itagaki, Y.; Nakanishi, K. "The ginkgolides. I. Isolation and characterization of the various groups". Tetrahedron Letter: 299–302. doi:10.1016/S0040-4039(00)71538-3. 
  4. ^ Dewick, P. M. Medicinal Natural Products: A Biosynthetic Approach (3rd ed.). Wiley. pp. 230–232. 
  5. ^ a b Zen, Z.; Zhu, J.; Chen, L.; Wen, W.; Yu, R. "Biosynthesis pathways of ginkgolides". Pharmacognosy Review 7 (13): 47–52. doi:10.4103/0973-7847.112848. 
  6. ^ Usai S, Grazzi L, Bussone G"Gingkolide B as migraine preventive treatment in young age: results at 1-year follow-up."Neurol Sci. 2011 May;32 Suppl 1:197-9
  7. ^ Usai, S.; Grazzi, L.; Bussone, G. "Gingkolide B as migraine preventive treatment in young age: results at 1-year follow-up". Neurol Sci. 32 (Suppl 1): SI97–SI99. doi:10.1007/s10072-011-0522-7. 
  8. ^ Dewick, P.M. (2012). Medicinal Natural Products: A Biosynthetic Approach (3rd Ed.). Wiley; 3 edition. pp. 230–232. ISBN 978-0470741672. 
  9. ^ Dewick, P.M. (2012). Medicinal Natural Products: A Biosynthetic Approach (3rd Ed.). United Kingdom: John Wiley and Sons, Ltd. pp. 230–232. ISBN 978-0470741672.