Chemistry of Natural Products Lecture 4 PDF
Document Details
Uploaded by Deleted User
Dr. Ghada Emad
Tags
Summary
This lecture covers terpenoids, including their isolation, separation, structure elucidation, and synthesis. The document discusses various methods, chemical reactions, and functional groups associated with these compounds. It provides valuable insights into the chemical properties of terpenoids.
Full Transcript
Dr. Ghada Emad Lecture 4 Isolation of Mono- and Sesequiterpenes *· (i) Expression *· (ii) Steam distillation *· (iii) Extraction by means of volatile organic solvents *· (iv) Adsorption on fats. Methods for...
Dr. Ghada Emad Lecture 4 Isolation of Mono- and Sesequiterpenes *· (i) Expression *· (ii) Steam distillation *· (iii) Extraction by means of volatile organic solvents *· (iv) Adsorption on fats. Methods for Separation of mixtures Fractional distillation Other methods high pressure liquid chromatography thin layer chromatography HPLC TLC column chromatography CC * General methods for structure determination of terpenoids *Analytical methods * Determination of % of C,H and O by combustion empirical formula molecular formula *Degrees of unsaturation *Estimation of groups *Active hydrogen *Terpene + LiA1H4 H2 ----- estimated *Chemical methods * Functional groups OH ,COOH, C6H5 * Unsaturation * by bromination (Br2) * by nitrosyl chloride NOCl Ozonolysis is an example of oxidative degradation methods (O3, KMnO4, CrO3 & OsO4). Conjugated and isolated double bonds are differentiated by Diel's Alder reaction. Dehydrogenation by heating the terpene with S or Se converts the terpene into aromatic derivative which is easily identified. * Hydrogenation of the substance to the parent hydrocarbon leads to the cyclic nature of the terpene (acyclic, monocyclic, bicyclic,.... etc). *· Hydrocarbon CnH2n+2 --------- Acyclic * CnH2n -------------- Monocyclic * CnH2n-2 ------------ Bicyclic * CnH2n-4 ----------- Tricyclic * CnH2n-6 ------------ Tetracyclic Degrees of unsat. = no. of H atoms in parent HC – no. of H atoms in compound/2 No. of cycles in molecules = Degrees of unsaturation – no. of double bonds *Physical and spectral methods *a) Molecular refraction (refractive index, refractometer). *b) Optical rotation D (polarimeter) *c) IR absorption *d) NMR (1H-NMR & 13C-NMR) *e) X-Ray analysis *f) UV (ultraviolet absorption) *· A final confirmation of the proposed structure is usually achieved by synthesizing the compound and comparing the spectral data with those of an authentic sample. Structure-elucidation and Synthesis of selected terpenoids * Myrcene, 13 acyclic unsubstituted monoterpene Myrcene 3 C10H16 1 O3 2 H2, Pt C10H22 maleic anhydride CH3COCH3 + 2 HCHO + adduct ketodialdehyde C 5H6O 3 4 [O] H2CrO 4 succinic acid +CO 2 13 I II III Geraniol and Nerol OH Ac2O 1 5 2 Br2 tetrabromo compd. OH acetate 2 esters C10H18Br4O PhCOCl 3 6 4 Pt, H2 14 15 [O] benzoate one saturated alc. * Geraniol 14 and Nerol 15 esters dil. H2SO4, C10H22O C10H18O aldehydes heat -terpineol 1.8 OH 16 OH 9 10 CH3 + H3C H OH C CH CH2 CH2 C CH CH2 OH H3C 7 6 5 4 3 2 1 8 OH cis or Z trans or E 16 + + OH2 + OH + H geraniol 14 + + OH H + OH nerol 15 _ + H H2O + OH OH2 + -terpineol 16 O O O * Ionones 18-20 Differentiate -ionone by -optically active -ionone 18 -ionone 19 -ionone 20 - UV Spectroscopy absorbs at α-ionone (228.5mµ), β ionone (296mµ) CHO O Ba(OH)2 + C H3C CH3 _ HOH CHO O O O + + H + -ionone 18 O O + _ H + -ionone 19 -ionone 20 *-Terpineol 16 C10H18O 7 1 6 2 -Terpineol Ac2O KMnO 4 5 3 4 acetate 1 5 trihydroxy compd. OH H2SO 4, C10H22O 3 p-menthane or 9 8 10 KHSO 4 2 16 hexahydro-p-cymene 3 4 heat Br2 C10H16 CrO 3 6 -H2O C10H18Br2O C10 ketohydroxy acid - H2O terebic acid C 7H10O 4 - ketolactone p cymene C10H16O 3 8 warm alk. KMnO 4 warm alk. KMnO 4 7 terpenylic acid C 8H12O 4 + acetic acid OH OH OH OH I II III IV OH OH CrO 3 O 1% alk. KMnO 4 COOH OH OH OH _ HOH HOOC COOH O O O O warm KMnO 4 O O warm KMnO4 + CO2 O + CH3COOH *Synthesis of -terpineol 16 SO 3H OH H2SO 4 i. KOH, fusion ii. H+ COOH COOH COOH p-toluic acid Na, EtOH Br OH pyridine HBr - HBr COOH COOH COOH EtOH, HCl i. 2 CH3MgI ii. H + COOEt OH Diels Alder i. CH3MgI reaction ii. H + OH O O *Limonene 23 Limonene 2 Br2 KHSO4 1 3 C10H16Br4 -terpineol p-cymene 23 tetrabromo compd. 2 dil. H2SO4 I II -terpineol *Citral 17 NH2OH Citral AgO2 oxime 1 3 acid C 10H16O C10H18O named geranic acid 2 4 Na(Hg), EtOH alk. KMnO4 then H2SO4 CHO alcohol C 10H18O COOH named geraniol O O COOH C + + CH3 CH3 COOH CH3 laevulic acid 9 10 CH3 CH3 1 5 3 CHO 7 C 6 4 C 2 CHO 8 CH2 H3C CH CH2 CH CHO citral-a or geranial citral-b or neral
