title: Synthesis of spirohydantoins and spiro-2,5-diketopiperazines via resin-bound cyclic alpha,alpha-disubstituted alpha-amino esters.
abstract: A seven-step solid-phase synthesis of spirohydantoins and an eight-step solid-phase synthesis of spiro-2,5-diketopiperazines is reported. Key intermediate in the synthesis of both compound libraries is the resin-bound cyclic alpha,alpha-disubstituted alpha-amino ester, which can be obtained after selective homogeneous reduction of the aliphatic nitro ester using tin(II) chloride dihydrate. Nitro ester, in turn, is synthesized by a high-pressure-assisted [4 + 2] cycloaddition of resin-bound nitro alkene and butadiene, whereas nitro alkene is obtained by a Knoevenagel condensation of resin-bound nitro acetate with an imine. Novel spirohydantoins are obtained by isocyanate coupling with the resin-bound amino ester 5, followed by cyclization cleavage using a base. Novel spiro-2,5-diketopiperazines are obtained by PyBOP coupling of a Fmoc-protected amino acid with resin-bound amino ester, followed by Fmoc deprotection and an acid-assisted cyclization cleavage. After preparation of seven different resin-bound alpha,alpha-disubstituted alpha-amino esters, a 7 x 8 compound library of spirohydantoins was synthesized using eight different isocyanates, and a 7 x 8 compound library of spiro-2,5-diketopiperazines was synthesized using eight different Fmoc amino acids.
authors.affiliation: Institute for Molecules and Materials, Radboud University Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands.
authors.forename: George J T
authors.initials: GJ
authors.lastname: Kuster
authors.forename: Leon W A
authors.initials: LW
authors.lastname: van Berkom
authors.forename: Mohamed
authors.initials: M
authors.lastname: Kalmoua
authors.forename: Arnold
authors.initials: A
authors.lastname: van Loevezijn
authors.forename: Leo A J M
authors.initials: LA
authors.lastname: Sliedregt
authors.forename: Bart J
authors.initials: BJ
authors.lastname: van Steen
authors.forename: Chris G
authors.initials: CG
authors.lastname: Kruse
authors.forename: Floris P J T
authors.initials: FP
authors.lastname: Rutjes
authors.forename: Hans W
authors.initials: HW
authors.lastname: Scheeren
mesh_terms: D000596:Amino Acids / Q000737:chemistry; D002853:Chromatography, Liquid; D020650:Combinatorial Chemistry Techniques / Q000379:methods*; D003500:Cyclization; D004952:Esters / Q000737:chemistry; D006827:Hydantoins / Q000138:chemical synthesis* / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D015394:Molecular Structure; D010879:Piperazines / Q000138:chemical synthesis* / Q000737:chemistry; D012117:Resins, Synthetic / Q000737:chemistry*; D013141:Spiro Compounds / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D000596:Amino Acids; D004952:Esters; D006827:Hydantoins; D010879:Piperazines; D012117:Resins, Synthetic; D013141:Spiro Compounds