13-Hydroxy gibberellins are dehydroxylated by esterifying the 13-hydroxy group with a sulphonic, carboxylic or thiocarboxylic acid or esterifiable derivative thereof and then reducing the 13-ester group with a tri-alkyltin hydride which is a selective reagent so that it is possible to remove a 13-hydroxy group in a gibberellin containing further hydroxy groups and/or lactone bridges. GA.sub.3 can be converted to GA.sub.7 by this process.

6' carbonate esters of zearalanol and its derivatives are used to promote growth in ruminants. The compounds have the structural formula: ##STR1## wherein R.sub.1 and R.sub.2, which may be the same or different, are H, X, or COX, where X is an alkyl group having from 1-6 carbon atoms; and R is an alkyl group or a Br or Cl substituted alkyl group having from 1-12 carbon atoms.

6' Carbamate esters of zearalanol and its derivatives are used to promote growth in ruminants. The compounds have the structural formula: ##STR1## wherein R.sub.1 and R.sub.2, which may be the same or different, are H, X, or COX, where X is an alkyl group having from 1-6 carbon atoms; and R is NH-Y, where Y is an alkyl group having from 1-6 carbon atoms or a five-membered or six-membered ring; N(C.sub.n H.sub.2n+1).sub.2, where n is an integer from 1 to 6; or a five-membered or six-membered heterocyclic ring having one N heteroatom and up to one other heteroatom selected from the group consisting of N, S, and O heteroatoms.

Ring opened halogenated Resorcyclic Acid Lactone (RAL) derivatives having the structure: ##STR1## are used to increase rumen fermentation efficiency.

The present invention relates to compounds having the structure (and pharmaceutically acceptable derivatives thereof) ##STR00001## wherein R.sub.0 R.sub.4, Z, X, A--B, D--E, G--J, and K--L are as defined herein, the synthesis thereof and the use of these compounds as therapeutic agents.