Natural Products and Stereochemistry

GENERAL OBJECTIVES:

1. Understand the different forms of spatial arrangement of atoms in molecules and differentiate between the various types of stereoisomers

2. Understand the sources and chemistry of some natural products.

3. Discuss the extraction of steroids” from yams and their conversion by partial synthesis into medically important steroid drugs

1.1 Explain the concept off isomerism.

1.2 Explain the following forms of stereoisomerism:

(a) conformational isomerism

(b) cis-trans isomerism in alkenes

(c) enantiomorphism

1.3 Define chirality.

1.4 Explain the interconvertability of conformers and the noninterconvertability of enantiomers (except via chemical reactions)

1.5 Explain optical activity of enantiomers.

1.6 Define specific rotation.

1.7 Write equation for calculating specific rotation.

1.8 Describe parameters that affect specific rotation.

1.9 Define absolute configuration.

1.10 List notations used in absolute configuration.

1.11 Define racemic mixture.

1.12 Explain racemic resolution.

1.13 Explain diastereisomerism.

1.14 Write the equation for the number of stereoisomers in a given compound.

1.15 Describe meso forms.

1.16 List example of meso forms.

1.17 Know that chiral compounds can not be synthesised from achiral compounds

1.18 Know that reaction of a pure enantiomer with an achiral reagent may give rise to a mixture of diastereoisomers in which one diastereoisomer predominates

1.19 Understand that the process involved above may result from steric effects as the reagents interact.

1.20 Discuss the phenethanolamines, their extraction from “Ma Huang” and other species of Ephedra

1.21 Discuss the stereochemistries of the various phenethanolamines and their medical uses.

2.1 Discuss what chemists mean by the term "Natural Products"

2.2 Describe, in brief outline, the history of the exploitation of natural products.

2.3 Discuss primary and secondary metabolites

2.4 Discuss some of the more important reactions used by nature in constructing natural products (e.g. oxidation, reduction, carbon-carbon bond forming reactions)

2.5 Describe the role of cofactors in the biosynthesis of natural products

2.6 Discuss the elucidation of biosynthetic pathways and the use of labelled precursors and metabolites

2.7 Describe the biosynthesis of fatty acids

2.8 Describe the biosynthesis and importance of prostaglandins and leukotrienes

2.9 Explain the meaning of alkaloids.

2.10 List alkaloids formed from plants and animal tissues.

2.11 Design a plan for the extraction of alkaloids from plant sources.

2.12 Describe the source, chemical structure, physiological activity and biosynthesis of ephedrine

2.13 Discuss the biosynthesis of selected alkaloids from ornithine and lysine

2.14 Discuss the biosynthesis and importance of nicotine

2.15 Discuss the biosynthesis and importance of the tropane alkaloids and cocaine

2.16 Discuss the biosynthesis of selected alkaloids from phenylalanine and tyrosine

2.17 Discuss the biosynthesis and importance of:reticulene, thebaine, codeine and morphine

2.18 Describe the source, chemical structure, physiological activity and biosynthesis of quinine

2.19 Explain the meaning of Terpenes.

2.20 List broad classes of terpenes.

2.21 Outline the sources of terpenes.

2.22 Discuss the biosynthesis of monoterpenes from mevalonic acid and isopentenyl pyrophosphate

2.23 Discuss the import monoterpenes: alpha pinene, and thujone

2.24 Discuss the biosynthesis of: Sesquitrpenes, C15; Diterpenes, C20; Triterpenes, C30 and Steroids

2.25 Explain the meaning of steroids.

2.26 List the sources of steroids.

2.27 Explain the importance of steroids in the synthesis of sex hormones

2.28 Describe the characterisation of steroids with reference to dicyclic acetal side chain.

2.29 Describe the synthesis of sex hormones from a named steroid.

2.30 Draw the structures of the following: Testosterone, Progesterone, Estrone, Stillbestrol, Cortocisterone, Aldosterone, Cortisone etc.

2.31 Explain the uses of steroids.

2.32 Synthesise sex hormones from named steroids

3.1 Discuss the expense of producing steroid drugs by total synthesis

3.2 Describe the search for natural sources of steroids from plants (to be used as raw materials for the synthesis of drugs)

3.3 Describe the discovery in yams of sapogenins with a "steroid-like" structure

3.4 Describe the conversion of diosgenin, by partial syntheses, into progesterone and androstenedione

3.5 Describe the conversion of androstenedione into estrone.

3.6 Discuss the stereochemistry resulting at centres produced by the above reactions and introduce the concept of stereospecific and stereoselective reactions.

3.7 Give examples of stereoselective reactions in the organic chemistry of steroids