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The influence of 2-alkyl-2-carboxyazeti
dines (Aze) on the 3D structure of mo
del tetrapepti
des R
2CO-2-R
1Aze-
L-Ala-NHMe has been analyze
d by molecular mo
deling,
1H NMR, an
d FT-IR stu
dies. Theconformational constraints intro
duce
d by the four-membere
d ring resulte
d in an effective way to stabilize
-turn-like conformations in these short pepti
des. The conformational preferences of these Aze-containingpepti
des have been compare
d to those of the correspon
ding pepti
de analogues containing Pro or
-MeProin the place of 2-alkyl-Aze resi
due. In the mo
del stu
die
d, both Pro an
d Aze
derivatives are able to in
ducereverse turns, but the nature of the turn is
different as a function of the ring size. While the five-membere
dring of Pro ten
ds to in
duce
ddle">-turns, as previously suggeste
d by
different authors, the four-membere
d ringof Aze resi
dues forces the pepti
de to preferentially a
dopt
-turn conformations. In both cases, the presenceof an alkyl group at the
-position of Pro or the azeti
dine-2-carboxylate ring enhances significantly theturn-in
ducing ability. These results might open the opportunity of using 2-alkyl-Aze resi
dues as versatiletools in
defining the role of
-turn structures within the bioactive conformation of selecte
d pepti
des, an
drepresent an alternative to Pro
derivatives as turn in
ducers.