Peptide Nanotubes: A Crystallographic Approach
97
R1 = H
R2 = H
ΔAla
R1 = CH3
R2 = H
Δ
Z Abu
R1 = CH3
R2 = CH3 ΔVal
R1 = CH(CH3)2 R2 = H
ΔLeu
R1 = C6H5
R2 = H
Δ
Z Phe
Fig. 2 The chemical structures of some of dehydroamino acids
introduces certain geometric alterations in dehydroresidues and restricts the conformational flexibility of dehydropeptide backbone and side chains of dehydroresidue.
These special features have influenced the use of α, β-dehydroamino acids in the
design of model peptides (Jain and Chauhan 1996; Mathur et al. 2004; Narula et al.
1998; Singh and Kaur 1996).
Dehydroalanine (Ala), dehydrovaline (Val), dehydroleucine (Val), dehydroaminobutyric acid (Abu), dehydroisoleucine (Ile), dehydroproline (Pro)
and dehydrophenylalanine (Phe) are some of the dehydroamino acids used in the
design of model peptides. However, dehydrophenylalanine is used in most of the
studies mainly because of its convenient chemical synthesis and interesting conformational restricting properties (Jain and Chauhan 1996; Mathur et al. 2004; Singh
and Kaur 1996). The chemical structures of some of these dehydroamino acids are
shown in Fig. 2.
2.1.1 α, β-dehydrophenylalanine (Phe) Residue
As mentioned earlier in the definition, it is an analogue of phenylalanine residue,
with a double bond between C
α and C
β atoms. It can exist in two isomeric forms,
Z-isomer (
Z Phe) and the E-isomer (
E Phe) (Noda et al. 1983) (Fig. 3). In the Zisomer the C=O group is in trans position with respect to the phenyl ring, while in the
E-isomer it is in cis position. Among these isomers, the conformational studies are
extensively done on Z-isomer due to the fact that most synthetic processes result in
Z-isomer (
Z Phe) and the E-isomer is sensitive to the chemical environment of the
synthetic procedure. However, recently E-isomer has been reportedly incorporated
in model peptide (Broda et al. 2005). The peptide work presented discussed here is
exclusively on Z-isomer (
Z Phe) and here afterwards we represent it by Phe or
F.
97
R1 = H
R2 = H
ΔAla
R1 = CH3
R2 = H
Δ
Z Abu
R1 = CH3
R2 = CH3 ΔVal
R1 = CH(CH3)2 R2 = H
ΔLeu
R1 = C6H5
R2 = H
Δ
Z Phe
Fig. 2 The chemical structures of some of dehydroamino acids
introduces certain geometric alterations in dehydroresidues and restricts the conformational flexibility of dehydropeptide backbone and side chains of dehydroresidue.
These special features have influenced the use of α, β-dehydroamino acids in the
design of model peptides (Jain and Chauhan 1996; Mathur et al. 2004; Narula et al.
1998; Singh and Kaur 1996).
Dehydroalanine (Ala), dehydrovaline (Val), dehydroleucine (Val), dehydroaminobutyric acid (Abu), dehydroisoleucine (Ile), dehydroproline (Pro)
and dehydrophenylalanine (Phe) are some of the dehydroamino acids used in the
design of model peptides. However, dehydrophenylalanine is used in most of the
studies mainly because of its convenient chemical synthesis and interesting conformational restricting properties (Jain and Chauhan 1996; Mathur et al. 2004; Singh
and Kaur 1996). The chemical structures of some of these dehydroamino acids are
shown in Fig. 2.
2.1.1 α, β-dehydrophenylalanine (Phe) Residue
As mentioned earlier in the definition, it is an analogue of phenylalanine residue,
with a double bond between C
α and C
β atoms. It can exist in two isomeric forms,
Z-isomer (
Z Phe) and the E-isomer (
E Phe) (Noda et al. 1983) (Fig. 3). In the Zisomer the C=O group is in trans position with respect to the phenyl ring, while in the
E-isomer it is in cis position. Among these isomers, the conformational studies are
extensively done on Z-isomer due to the fact that most synthetic processes result in
Z-isomer (
Z Phe) and the E-isomer is sensitive to the chemical environment of the
synthetic procedure. However, recently E-isomer has been reportedly incorporated
in model peptide (Broda et al. 2005). The peptide work presented discussed here is
exclusively on Z-isomer (
Z Phe) and here afterwards we represent it by Phe or
F.