title: Self-assembling, cystine-derived, fused nanotubes based on spirane architecture: design, synthesis, and crystal structure of cystinospiranes.
abstract: A novel family of cystine-based spirobicyclic peptides (cystinospiranes) has been synthesized by a single-step procedure involving condensation of pentaerythritol-derived tetrachloride with either the simple L-cystine dimethyl ester or its C,C'-extended bispeptides leading to a variety of 19-membered spirobicyclic peptides or its N,N'-extended bispeptides affording the ring-expanded 25-membered cystinospiranes. The design is flexible with respect to the ring size that can be adjusted depending upon the length of the N,N'-extended cystine bispeptide, and the choice of an amino acid, as illustrated here with the preparation of a large number of cystinospiranes containing a wide variety of amino acids. X-ray crystal structure of the parent spirane (5a) revealed nanotube formation by vertical stacking of relatively flat spirobicyclic molecules through contiguous NH- - -O==C hydrogen bonding. The fused pair of parallel nanotubes is open-ended, hollow, and extends to infinity. Crystallographic parameters are the following: C(33)H(52)N(4)O(16)S(4), space group C2, a = 42.181(3) A, b = 5.1165(7) A, c = 11.8687(9) A, beta = 106.23(1) degrees.
authors.affiliation: Discovery Laboratory, Indian Institute of Chemical Technology, Hyderabad-500 007, India. ranganathan@iict.ap.nic.in
authors.forename: D
authors.initials: D
authors.lastname: Ranganathan
authors.forename: M P
authors.initials: MP
authors.lastname: Samant
authors.forename: I L
authors.initials: IL
authors.lastname: Karle
mesh_terms: D003460:Crystallization; D018360:Crystallography, X-Ray; D003553:Cystine / Q000737:chemistry*; D006860:Hydrogen Bonding; D015394:Molecular Structure; D010456:Peptides, Cyclic / Q000138:chemical synthesis* / Q000737:chemistry; D017433:Protein Structure, Secondary; D013141:Spiro Compounds / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D010456:Peptides, Cyclic; D013141:Spiro Compounds; D003553:Cystine