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  • 1
    ISSN: 1434-193X
    Keywords: Peptidomimetics ; Octahydro[2H]pyrazino[1,2-a]pyrazine ; Diastereoselectivity ; Tripeptides ; Crystal structures ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: -A new route to octahydrospiro(cyclopropane-1,1′-[2H]-pyrazino[1,2-a]pyrazine)-3′,6′,9′-triones 12-15 has been developed. Michael additions of primary amines onto methyl 2-Me or tert-butyl 2-tBu 2-chloro-2-cyclopropylideneacetates, followed by DCC- or EDC-induced coupling with Boc- or FmocGlyOH, deprotection and cyclization led to α-amino esters 4a-c and chlorohexahydrodiazepinediones 5a-c, or in the case of 2-tBu to the α-amino ester 7 exclusively. This reaction sequence with (S)-BocPheOH and (S)-BocTrpOH diastereoselectively gave (3′R,5′S)-9a,b and (2′S,6′R)-11a,b as the main products. Further peptide coupling, deprotection and cyclization with 4a-c yielded octahydrospiro(cyclopropane-1,1′-[2H]pyrazino[1,2-a]pyrazine)-3′,6′,9′-triones (7′S,9a′S)-12a-d, (6a′S,11a′S)-12e, (7′S,9a′R)-13a-d and (6a′S,11a′R)-13e which were easily separated. The α-amino esters 9a,b yielded (4′S,9a′R)-14a (≡15a) and (4′S,9a′R)-14b (≡15b), (4′S,7′S,9a′R)-14c and (4′R*,7′S*,9a′S*)-15c. The formation of compounds with three stereogenic centers 14c and 15c was accompanied by partial racemization. The versatility of the reported reaction sequence is limited by the steric availability of the secondary amino group in the intermediates 4, 9 and 10, as well as in the Michael adducts formed from primary amines and 2-Me.
    Additional Material: 4 Ill.
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  • 2
    ISSN: 1434-193X
    Keywords: Amino acids ; Spiro compounds ; Michael addition ; Copper reagents ; Curtius degradation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Racemic spiropentylglycine (8) has been synthesized by sodium borohydride reduction of benzyl (E/Z)-2-chloro-2-spiropentylideneacetate (5-Bn), nucleophilic substitution of the chlorine in the product 6 with azide and hydrogenolytic deprotection of the resulting 7 (overall yield 15%). An alternative approach to 8 consisted of the coupling of the higher-order cuprate 10, generated by halogen-metal exchange from bromospiropentane (9), with the electrophilic glycine equivalent 11 followed by deprotection (overall yield 47%). Enantiomerically pure (1′-aminospiropentyl)acetic acid [(R)-16] (overall yield 16% from 5-Me) and 1-aminospiropentanecarboxylic acid [(R)-23] (29% from 5-Me) were obtained from the Michael adduct 14-Me of (4R,5S)-4,5-diphenyloxazolidin-2-one (13) and methyl (E/Z)-2-chloro-2-spiropentylideneacetate (5-Me). Racemic 1-aminospiropentanecarboxylic acid (R/S-23) was prepared by rhodium-catalyzed addition of dimethyl diazomalonate to methylenecyclopropane and subsequent Curtius degradation of the halfester 28 via the azide 29 (overall yield 14%). Upon standing in aqueous solution, 23 underwent complete rearrangement to the new 1-amino-2-methylenecyclobutanecarboxylic acid (24). The interesting derivative of azabicyclo[3.1.0]hexane-1-carboxylate 34 with an annelated spiropentane moiety and a β-amino acid fragment was incidentally obtained in a one-step intermolecular domino reaction starting with the addition of lithium benzylamide to methyl 2-chloro-2-cyclopropylideneacetate (32, 41% yield).
    Additional Material: 2 Ill.
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