title: A delineation of diketopiperazine self-assembly processes: understanding the molecular events involved in Nepsilon-(fumaroyl)diketopiperazine of L-Lys (FDKP) interactions.
abstract: The Nepsilon-fumaroylated diketopiperazine of L-Lys (FDKP, 1) self-assembles into microparticles that can be used for pulmonary drug delivery. When these particles are formulated with insulin, the resultant powder (Technosphere Insulin) provides a novel prandial insulin therapy. To better understand the self-assembly of 1, a series of model compounds were synthesized that allowed for the determination of the preferred intramolecular hydrogen-bonding pattern of FDKP. Variable-temperature NMR (CDCl3) and FTIR studies of acyclic diamides (3-7a) and diketopiperazine models (7b- 9d) revealed the preference of a 10-membered hydrogen bond between one of the diketopiperazine's amido NH and the appended fumaramido-carbonyl (assigned as a "type B" H bond). Molecular modeling studies identified a low energy conformer in the architecture of 1, which contains two Nepsilon-fumaroylated lysine side chains appended to the diketopiperazine core. The lowest energy form involved a "cooperative" hydrogen bond motif which involved only one of the diketopiperazine amides and had one "arm" involved in a type B motif and the other in a "type A" hydrogen bond (i.e., the fumaramidyl NH H-bonding to the diketopiperazine amide carbonyl). This cooperative hydrogen bond scenario orients the appended fumaryl groups into a distinctive 90 degrees arrangement and is likely involved in its self-assembly into microparticles.
authors.affiliation: ophansti@mail.ucf.edu.
authors.forename: Navneet
authors.initials: N
authors.lastname: Kaur
authors.forename: Bo
authors.initials: B
authors.lastname: Zhou
authors.forename: Fred
authors.initials: F
authors.lastname: Breitbeil
authors.forename: Katherine
authors.initials: K
authors.lastname: Hardy
authors.forename: Kelly S
authors.initials: KS
authors.lastname: Kraft
authors.forename: Iva
authors.initials: I
authors.lastname: Trantcheva
authors.forename: Otto
authors.initials: O
authors.lastname: Phanstiel
mesh_terms: D005650:Fumarates / Q000737:chemistry*; D006860:Hydrogen Bonding; D008239:Lysine / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D010879:Piperazines / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D013696:Temperature
chemical_list: D005650:Fumarates; D010879:Piperazines; D008239:Lysine; C413290:3,6-bis(N-fumaryl-N(n-butyl)amino)-2,5-diketopiperazine