Substituted diphenylmethyl protecting groups in peptide synthesis

Direct Access to N-H-Aziridines from Asymmetric Catalytic Aziridination with Borate Catalysts Derived from Vaulted Binaphthol and Vaulted Biphenanthrol Ligands

The asymmetric catalytic aziridination reaction (AZ reaction) of N-dianisylmethylimines (N-DAM-imines) with ethyl diazoacetate is developed with chiral catalysts prepared from triphenylborate and both the vaulted binaphthol (VANOL) and vaulted biphenanthrol (VAPOL) ligands. Catalysts derived from both ligands were equally effective in terms of asymmetric induction, but the VANOL catalyst was slightly faster. Up to 400 turnovers could be achieved with the VANOL catalyst while still maintaining>or=90% ee in the aziridine product. The ligand could be recovered in 95% yield with no loss in optical purity. Excellent asymmetric inductions were observed with arylimines, and although slightly lower inductions were observed for alkyl-substituted imines, the optical purity of the aziridines from all of the imine substrates could be enhanced to>or=99% ee with a single crystallization. Methods were developed for deprotection of the N-DAM-aziridines under acidic conditions without causing an acid-promoted opening of the ring. Excellent yields of the N-H-aziridines could be obtained with both alkyl- and aryl-substituted aziridines. Finally, activation of the N-H-aziridines was achieved with Boc, tosyl, and Fmoc groups. The activated aziridines can be converted to beta3-amino esters, and unexpectedly, the N-Boc-protected aziridine-2-carboxylate 16b with a phenyl substituent in the 3-position cis to the ester group was found to undergo ring expansion to a mixture of cis- and trans-oxazolidinones.

Novel analogues of degarelix incorporating hydroxy-, methoxy-, and pegylated-urea moieties at positions 3, 5, 6 and the N-terminus. Part III

Novel degarelix (Fe200486) analogues were screened for antagonism of GnRH-induced response (IC(50)) in a reporter gene assay. Inhibition of luteinizing hormone release over time was measured in the castrated male rat. N(omega)-Hydroxy- and N(omega)-methoxy-carbamoylation of Dab and Dap at position 3 (3-6), and N(omega)-hydroxy-,N(omega)-methoxy-carbamoylation and pegylation of 4Aph at positions 5 and 6 (7-10, 15-17, 22-25) were carried out. Modulation of hydrophobicity was achieved using different acylating groups at the N-terminus (11-14, 18-21, 26-28). Analogues 8, 15-17, 22, and 23 were equipotent to acyline (IC(50) = 0.69 nM) and degarelix (IC(50) = 0.58 nM) in vitro. Analogues 7, 17, and 23 were shorter acting than acyline, when 9, 11, 13, 15, 16, and 22 were longer acting. Only 9 and 14 were inactive at releasing histamine. No analogue exhibited a duration of action comparable to that of degarelix. Analogues with shorter and longer retention times on HPLC (a measure of hydrophilicity) than degarelix were identified.

Iterative approach to the discovery of novel degarelix analogues: substitutions at positions 3, 7, and 8. Part II

Degarelix (FE200486, Ac-d-2Nal(1)-d-4Cpa(2)-d-3Pal(3)-Ser(4)-4Aph(l-Hor)(5)-d-4Aph(Cbm)(6)-Leu(7)-ILys(8)-Pro(9)-d-Ala(10)-NH(2)) is a potent and very long acting antagonist of gonadotropin-releasing hormone (GnRH) after subcutaneous administration in mammals including humans. Analogues of degarelix were synthesized, characterized, and screened for the antagonism of GnRH-induced response in a reporter gene assay in HEK-293 cells expressing the human GnRH receptor. The duration of action was also determined in the castrated male rat assay to measure the extent (efficacy and duration of action) of inhibition of luteinizing hormone (LH) release. Structurally, this series of analogues has novel substitutions at positions 3, 7, and 8 and N(alpha)-methylation at positions 6, 7, and 8 in the structure of degarelix. These substitutions were designed to probe the spatial limitations of the receptor's cavity and to map the steric and ionic boundaries. Some functional groups were introduced that were hypothesized to influence the phamacokinetic properties of the analogues such as bioavailability, solubility, intra- or intermolecular hydrogen bond forming capacity, and ability to bind carrier proteins. Substitutions at positions 3 ([N(beta)-(2-pyridyl-methyl)d-Dap(3)]degarelix, IC(50) = 2.71 nM) (5), 7 ([Pra(7)]degarelix, IC(50) = 2.11 nM) (16), and 8 ([N(delta)-(IGly)Orn(8)]degarelix, IC(50) = 1.38 nM) (20) and N-methylation ([N(alpha)-methyl-Leu(7)]degarelix, IC(50) = 1.47 nM) (32) yielded analogues that were equipotent to degarelix (2) in vitro (IC(50) = 1.64 nM) but shorter acting in vivo. Out of the 33 novel analogues tested for the duration of action in this series, two analogues ([N(epsilon)-cyclohexyl-Lys(8)]degarelix, IC(50) = 1.50 nM) (23) and ([N(beta)-(IbetaAla)Dap(8)]degarelix, IC(50) = 1.98 nM) (26) had antagonist potencies and duration of action similar to that of azaline B {inhibited LH (>80%) release for >72 h after sc injection to castrated male rats at a standard dose of 50 mug/rat in 5% mannitol}. Under similar conditions analogues ([N(gamma)-(IGly)Dab(8)]degarelix, IC(50) = 1.56 nM) (21) and ([IOrn(8)]degarelix, IC(50) = 1.72 nM) (18) had a longer duration of action {inhibited LH (>96 h) release} than azaline B; however they were shorter acting than degarelix. Hydrophilicity of these analogues, a potential measure of their ability to be formulated for sustained release, was determined using RP-HPLC at neutral pH yielding analogues with shorter as well as longer retention times. No correlation was found between retention times and antagonist potency or duration of action.

Enantiospecific Formation of Trans 1,3-Disubstituted Tetrahydro-beta-carbolines by the Pictet-Spengler Reaction and Conversion of Cis Diastereomers into Their Trans Counterparts by Scission of the C-1/N-2 Bond

The factors which effect the stereoselective formation of trans-1-alkyl-2-benzyl-3-(alkoxycarbonyl)-1,2,3,4-tetrahydro-beta-carbolines and trans-3-(alkoxycarbonyl)-1-alkyl-2-(diphenylmethyl)-1,2,3,4-tetrahydro-beta-carbolines by the Pictet-Spengler cyclization were examined by heating tryptophan derivatives with aldehydes of varied steric bulk under aprotic and acidic conditions, followed by determination of the ratio of cis to trans diastereomers so formed. The presence of a benzyl group at the N(b)-nitrogen atom alters the diastereochemical outcome of this condensation to provide 100% trans stereoselectivity when the cyclization is carried out with cyclohexanecarboxaldehyde. Furthermore, when N(b)-(diphenylmethyl)tryptophan isopropyl ester was condensed with aldehydes of any size, trans diastereomers are formed with 100% stereoselectively. The trans N(b)-substituted diastereomers are thermodynamically more stable than their cis congeners as shown by equilibration experiments in TFA. Conversion of the cis diastereomers into the more stable trans diastereomers is believed to occur under acidic conditions by cleavage of the carbon (C-1)-nitrogen (N-2) bond with complete retention of configuration at the C-3 stereocenter. Evidence from deuterium exchange experiments as well as optical rotations support this model for epimerization. In addition, when cis diastereomer 66a was allowed to stir in CF(3)COOD, the trans isomer 66b was isolated in 90% yield, while treatment of cis 66a with CF(3)COOH/NaBH(4) provided a mixture of the ring cleaved [scission across C(1)-N(2) bond] product 67 and the trans isomer 66b. Treatment of 66b (control experiment) with NaBH(4)/CF(3)COOH under the same conditions returned only starting trans 66b in excellent yield. The Pictet-Spengler reaction of substrates with sufficiently large substituents, followed by treatment with acid, permits the 100% enantiospecific formation of trans-1,3-disubstituted-1,2,3,4-tetrahydro-beta-carbolines for alkaloid total synthesis.