1. A process for preparing an extract of a plant of the genus Trichocaulon or of the genus Hoodia, the extract comprising an appetite suppressant agent having the general structural formula (2)   in which R = alkyl; R1 = H, alkyl, tigloyl, benzoyl, or any other organic ester group; R2 = H, or one or more 6-deoxy carbohydrates, or one or more 2,6-dideoxy carbohydrates, or glucose molecules, or combinations thereof; and in which the broken lines indicate the optional presence of a further bond between C4-C5 or C5-C6, the process including the steps of treating collected plant material with a solvent to extract a fraction having appetite suppressant activity, separating the extraction solution from the rest of the plant material, removing the solvent from the extraction solution and recovering the extract. 2. A process as claimed in Claim 1 wherein the plant of the genus Trichocaulon is selected from the species Trichocaulon piliferum and Trichocaulon officinale and the plant of the genus Hoodia is selected from the species Hoodia currorii, Hoodia gordonii and Hoodia lugardii. 3. A process as claimed in Claim 1 or Claim 2 which includes the step of concentrating the active agent in the extracted material by further extraction with a solvent. 4. A process as claimed in any one of Claims 1 to 3, wherein the solvent in the solvent extraction step or steps is one or more of methylene chloride, water, methanol, hexane, ethyl acetate or mixtures thereof. 5. A process as claimed in any one of Claims 1 to 4 inclusive which includes the step of concentrating the active agent in the extracted material by chromatographic separation. 6. A process as claimed in Claim 5 wherein the chromatographic separation employs one or more of chloroform, methanol, ethyl acetate, hexane or mixtures thereof as an eluant. 7. A process as claimed in Claim 5 or 6 which includes carrying out the chromatographic separation on a column, collecting the eluate in fractions from the column, evaluating the fractions to determine their appetite suppressant activity, and selecting the at least one fraction containing the appetite suppressant agent. 8. A process as claimed in any of the preceding Claims wherein the extract is processed to form a free-flowing powder. 9. An extract comprising an appetite suppressant agent when produced by a process as claimed in any of the preceding Claims. 10. A composition having appetite suppressant activity comprising the extract claimed in Claim 9. 11. A composition as claimed in Claim 10 when admixed with a pharmaceutical excipient, diluent or carrier. 12. A composition as claimed in Claim 10 or 11 which is prepared in unit dosage form. 13. The use of an extract as claimed in Claim 9 in the manufacture of a medicament having appetite suppressant activity. 14. An extract as claimed in Claim 9 for use as a medicament having appetite suppressant activity. 15. A method of suppressing an appetite by administering to a human or animal an effective dosage of a composition as claimed in Claim 10, 11, or 12. 16. A process as claimed in Claim 1 including the steps of pressing collected plant material to separate sap from solid plant material and recovering the sap free of the solid plant material to form the extract. 17. A process as claimed in Claim 16 wherein the extract is dried to form a free-flowing powder. 18. An extract comprising an appetite suppressant agent when produced by a process as claimed in Claim 16 or 17. 19. A composition having appetite suppressant activity comprising the extract as claimed in Claim 18. 20. A composition as claimed in Claim 19 when admixed with a pharmaceutical excipient, diluent or carrier. 21. A composition as claimed in Claim 19 or Claim 20 which is prepared in unit dosage form. 22. The use of an extract as claimed in Claim 19 in the manufacture of a medicament having appetite suppressant activity. 23. An extract as claimed in Claim 18 for use as a medicament having appetite suppressant activity. 24. A method of suppressing an appetite by administering to a human or animal an effective dosage of a composition as claimed in Claim 19, 20, or 21. 25. An extract obtainable from a plant of the genus Trichocaulon or of the genus Hoodia which comprises an appetite suppressant agent having the formula   26. An extract as claimed in Claim 25 wherein the plant of the genus Trichocaulon is selected from the species Trichocaulon piliferum and Trichocaulon officinale and the plant of the genus Hoodia is selected from the species Hoodia currorii, Hoodia gordonii and Hoodia lugardii. 27. An extract as claimed in Claim 26 wherein substantially all the non-active impurities have been removed. 28. An extract as claimed in any one of Claims 25 to 27 inclusive which has been processed to a free-flowing powder. 29. A composition having appetite suppressant activity comprising the extract as claimed in any one of Claims 25 to 28 inclusive. 30. A composition as claimed in Claim 29 when admixed with a pharmaceutical excipient, diluent or carrier. 31. A composition as claimed in Claim 29 or Claims 30 which is prepared in unit dosage form. 32. The use of an extract as claimed in any one of Claims 25 to 28 inclusive in the manufacture of a medicament having appetite suppressant activity. 33. An extract as claimed in any one of Claims 25 to 28 inclusive for use as a medicament having appetite suppressant activity. 34. A method of suppressing an appetite by administering to a human or animal an effective dosage of a composition as claimed in Claim 29, 30 or 31. 35. A compound having the general structural formula (2)   in which R = alkyl; R1 = H, alkyl, tigloyl, benzoyl, or any other organic ester group; R2 = H, or one or more 6-deoxy carbohydrates, or one or more 2,6-dideoxy carbohydrates, or glucose molecules, or combinations thereof; and in which the broken lines indicate the optional presence of a further bond between C4-C5 or C5-C6. 36. A compound as claimed in Claim 35 wherein there is a bond between C5- C6, R = methyl, R1 = tigloyl, R2 = 30- [β-D-thevetopyranosyl-(1~4)- αβ-D-cymaropyranosyl-(1~4)- β-D-cymaropyranosyl], the compound having the structural formula   37. A compound having the general structural formula   in which R = alkyl; and R1 = H, alkyl, tigloyl, benzoyl, or any other organic ester group. 38. A compound having the general structural formula   in which R = alkyl; and R1 = H, alkyl, tigloyl, benzoyl, or any other organic ester group. 39. A compound having the general structural formula   in which R = alkyl; and R1 = H, alkyl, tigloyl, benzoyl, or any other organic ester group. 40. A compound having the general structural formula   in which R = alkyl; and R1 = H, alkyl, tigloyl, benzoyl, or any other organic ester group. 41. A compound having the general structural formula   in which R = alkyl; R1 = H, alkyl, tigloyl, benzoyl, or any other organic ester group. 42. A compound having the general structural formula   in which R = alkyl; and R1 = H, alkyl, tigloyl, benzoyl, or any other organic ester group; R2 = H, or one or more 6-deoxy carbohydrates, or one or more 2,6-dideoxy carbohydrates, or glucose molecules, or combinations thereof; and in which the broken lines indicate the optional presence of a further bond between C4 - C5 or C5 - C6. 43. A compound having the general structural formula   in which R = alkyl; and R1 = H, alkyl, tigloyl, benzoyl, or any other organic ester group; R2 = H, or one or more 6-deoxy carbohydrates, or one or more 2,6-dideoxy carbohydrates, or glucose molecules, or combinations thereof; and in which the broken lines indicate the presence of a further bond between C4 - C5 or C5 - C6. 44. A compound having the general structural formula   in which R = alkyl; and R1 = H, alkyl, tigloyl, benzoyl, or any other organic ester group; R2 = H, or one or more 6-deoxy carbohydrates, or one or more 2,6-dideoxy carbohydrates, or glucose molecules, or combinations thereof; and in which the broken lines indicate the optional presence of a further bond between C4 - C5 or C5 - C6. 45. A compound having the general structural formula   in which R = alkyl; and R1 = H, alkyl, tigloyl, benzoyl, or any other organic ester group; R2 = H, or one or more 6-deoxy carbohydrates, or one or more 2,6-dideoxy carbohydrates, or glucose molecules, or combinations thereof; and in which the broken lines indicate the optional presence of a further bond between C4 - C5, C5 - C6 or C14 - C15. 46. A compound having the general structural formula   in which R = alkyl; and R1 = H, alkyl, tigloyl, benzoyl, any other organic ester group; R2 = H, or one or more 6-deoxy carbohydrates, or one or more 2,6-dideoxy carbohydrates, or glucose molecules, or combinations thereof; and in which the broken lines indicate the optional presence of a further bond between C4 - C5, C5 - C6 or C14 - C15. 47. A compound having the general structural formula   in which R = alkyl; and R1 = H, alkyl, tigloyl, benzoyl, any other organic ester group; R2 = H, or one or more 6-deoxy carbohydrates, or one or more 2,6-dideoxy carbohydrates, or glucose molecules, or combinations thereof; and in which the broken lines indicate the optional presence of a further bond between C4 - C5, C5 - C6 or C14 - C15; and R3 = H, alkyl, aryl, acyl, or glucoxy. 48. A compound having the general structural formula   in which R = H, alkyl, aryl, or any steroid possessing a C14 beta hydroxy group, a C12 beta hydroxy functionality, a C17 acyl group, a C5 - C6 olefin, or combinations thereof. 49. A process for the preparation of a steroid intermediate of the formula   which includes the steps of (a) treating the compound   with a reducing agent to produce a compound 3β,12β-dihydroxy-20,20-ethylenedioxypregna-5,14-diene of the formula    (b) treating compound (23) with N-bromoacetamide (NBA) and a base to produce a compound 3β,12β-dihydroxy-14,15-epoxy-20,20-ethylenedioxypregn-5-ene of the formula   (c) treating comp