Fourcyclicpentapeptides and two cyclic heptapeptides modelled on the 310 helical Pro138-Gly144 segment of the water channel aquaporin-4 (AQP4) postulated to mediate adhesive interactions between AQP4 tetramers were synthesised by olefin metathesis. Three related acyclic pentapeptides Boc-Ser(All)-Xaa1-Val-Ser(All)-Gly-OMe (Xaa1 = Val, Aib; Boc = tert-butoxycarbonyl; All = allyl) and Boc-Ser(Bn)-Val-Val-Gly-Gly-OMe
A peptide comprising a unit of formula (I) and having a molecular weight of less than 2000 wherein each X is independently an organic group, e.g. a C
1-6
alkyl or C
1-6
alkenyl group, preferably —CH
2
—CH═CH
2
, or the two X groups taken together can form a covalent or non-covalent link between the two O groups, preferably a C
1-10
saturated or unsaturated carbon chain optionally interrupted by one or more heteroatoms selected from O, S, N, P, or Si, especially a C
3-10
carbon chain or one X represents an azido group and the other an C2-6-alkynyl group; both Z's are the same and are O or S; each Y is independently C, CH, CH
2
, N or NH; R
1
is H or C
1-6
alkyl; R
2
is H or C
1-6
alkyl; R
5
is a C
1-6
alkyl group, preferably isopropyl; or a salt, ester or prodrug thereof.