| abstract |
Synthetic novel cyclic hexapeptides having the structure: n Cyclo[(N-alkylamino acid)-X-(N-alkylamino acid)'-X-(N-alkylamino acid)"-X] n wherein (N-alkylamino acid), (N-alkylamino acid)' and (N-alkylamino acid)" have the structure: ##STR1## wherein R 1 is a lower alkyl group having 1 to 3 carbon atoms and R 2 is hydrogen and methyl or R 1 and R 2 are --CH 2 --N, n being an integer 2 or 3, and form a 4- or 5- membered ring; and X is D- or L-Ala, D- or L-Phe, D- or L-Leu, D- or L-p-halophenylalanyl or D- or L-p-nitrophenylalanyl, with the proviso that when R 1 is methyl and R 2 is hydrogen, X is not D-Ala are prepared. Oral administration of these cyclic peptides improves the digestive efficiency of certain herbivorous animals. |