TY - JOUR
T1 - 97. Synthesis of Unnatural Lipophilic N-(9H-Fluoren-9-ylmethoxy)carbonyl-Substituted α-Amino Acids and Their Incorporation into Cyclic RGD-Peptides
T2 - A Structure-Activity Study
AU - Koppitz, Marcus
AU - Huenges, Martin
AU - Gratias, Rainer
AU - Kessler, Horst
AU - Goodman, Simon L.
AU - Jonczyk, Alfred
PY - 1997
Y1 - 1997
N2 - The ανβ3 integrin is implicated in human tumor metastasis and angiogenesis. It has been shown that structures of the sequence cyclo(-Arg1-Gly2-Asp3-D-Phe 4-Xaa5-) (I) and cyclo(-Arg1-Gly2-Asp3-Phe 4-D-Xaa5-) (II) bind with high affinity and the latter with high selectivity to this receptor. The residues Xaa and D-Xaa accept a broad variety of amino acids. Here, we report on the synthesis, activities, and conformational analysis of cyclic Arg-Gly-Asp (RGD) peptides containing lipophilic amino acids Xaa or D-Xaa in position 5. For I, these were (2S)-2-aminohexadecanoic acid (Ahd) and N-hexadecylglycine (Hd-Gly) and in II, D-Ahd and Hd-Gly, and, for control purposes, Ahd were incorporated (Fig. 1). The enantiomerically pure α-amino acids were obtained by non-enantioselective synthesis and subsequent enzymatic separation of isomers using acylase I (Scheme). Hd-Gly was prepared in a modified procedure according to Stewart from ethyl bromoacetate and hexadecylamine (Scheme). The synthesis and physicochemical properties of the corresponding (9H-fluoren-9-ylmethoxy)carbonyl (Fmoc) derivatives, compatible with solid-phase peptide synthesis, are described. Structure elucidation by NMR reveals that the lipid modification has no significant impact on the template structures when incorporated into them. For peptides I with Xaa = Ahd or Hd-Gly (1 or 2), a βII′/γ-turn-like arrangement with D-Phe in i + 1 position of the β-turn is found. Peptides II with D-Xaa = D-Ahd or Hd-Gly (3 or 4) exhibit a βII′/γ-turn conformation with Gly in i + 1 position of the β-turn, whereas II with Ahd instead of D-Xaa, i.e., lacking a D-amino acid in position 4 or 5 (5), adopts no defined conformation. However, in assays of receptor specificity employing human ανβ3 integrin, the compounds exhibit IC50 values ranging from nanomolar to less than millimolar. These results indicate that although the arrangement of the pharmacophoric groups is preserved in the target compounds, the biological activity is highly dependent on spatial requirements of the lipid anchor in the receptor binding pocket. Obviously, only certain positions do not affect the binding.
AB - The ανβ3 integrin is implicated in human tumor metastasis and angiogenesis. It has been shown that structures of the sequence cyclo(-Arg1-Gly2-Asp3-D-Phe 4-Xaa5-) (I) and cyclo(-Arg1-Gly2-Asp3-Phe 4-D-Xaa5-) (II) bind with high affinity and the latter with high selectivity to this receptor. The residues Xaa and D-Xaa accept a broad variety of amino acids. Here, we report on the synthesis, activities, and conformational analysis of cyclic Arg-Gly-Asp (RGD) peptides containing lipophilic amino acids Xaa or D-Xaa in position 5. For I, these were (2S)-2-aminohexadecanoic acid (Ahd) and N-hexadecylglycine (Hd-Gly) and in II, D-Ahd and Hd-Gly, and, for control purposes, Ahd were incorporated (Fig. 1). The enantiomerically pure α-amino acids were obtained by non-enantioselective synthesis and subsequent enzymatic separation of isomers using acylase I (Scheme). Hd-Gly was prepared in a modified procedure according to Stewart from ethyl bromoacetate and hexadecylamine (Scheme). The synthesis and physicochemical properties of the corresponding (9H-fluoren-9-ylmethoxy)carbonyl (Fmoc) derivatives, compatible with solid-phase peptide synthesis, are described. Structure elucidation by NMR reveals that the lipid modification has no significant impact on the template structures when incorporated into them. For peptides I with Xaa = Ahd or Hd-Gly (1 or 2), a βII′/γ-turn-like arrangement with D-Phe in i + 1 position of the β-turn is found. Peptides II with D-Xaa = D-Ahd or Hd-Gly (3 or 4) exhibit a βII′/γ-turn conformation with Gly in i + 1 position of the β-turn, whereas II with Ahd instead of D-Xaa, i.e., lacking a D-amino acid in position 4 or 5 (5), adopts no defined conformation. However, in assays of receptor specificity employing human ανβ3 integrin, the compounds exhibit IC50 values ranging from nanomolar to less than millimolar. These results indicate that although the arrangement of the pharmacophoric groups is preserved in the target compounds, the biological activity is highly dependent on spatial requirements of the lipid anchor in the receptor binding pocket. Obviously, only certain positions do not affect the binding.
UR - http://www.scopus.com/inward/record.url?scp=0030797714&partnerID=8YFLogxK
U2 - 10.1002/hlca.19970800423
DO - 10.1002/hlca.19970800423
M3 - Article
AN - SCOPUS:0030797714
SN - 0018-019X
VL - 80
SP - 1280
EP - 1300
JO - Helvetica Chimica Acta
JF - Helvetica Chimica Acta
IS - 4
ER -