Design and Synthesis of a 3,4-Dehydroproline Amide Discovery Library

Diverging DOS strategy using an allene-containing tryptophan scaffold and a library design that maximizes biologically relevant chemical space while minimizing the number of compounds

A diverging diversity-oriented synthesis (DOS) strategy using an allene-containing tryptophan as a key starting material was investigated. An allene-yne substituted derivative of tryptophan 12 gave indolylmethylazabicyclooctadiene 17 when subjected to a microwave-assisted allenic [2 + 2] cycloaddition reaction. This same tryptophan-derived precursor afforded an indolylmethyldihydrocyclopentapyridinone 14 when subjected to a rhodium(I)-catalyzed cyclocarbonylation reaction and an indolylmethylpyrrolidinocyclopentenones 16 when reacted with molybdenum hexacarbonyl. Construction of allenic tetrahydro-β-carboline scaffolds via a Pictet-Spengler reaction and subsequent silver(I)-catalyzed cycloisomerization afforded tetrahydroindolizinoindoles (21). Attachment of allene and alkyne groups to the tetrahydro-β-carboline, followed by a microwave-assisted allenic [2 + 2] cycloaddition reaction, provided tetrahydrocyclobutaindoloquinolizinones 24 and the tetrahydrocyclopentenone indolizinoindolone 26 when reacted with molybdenum hexacarbonyl. These six scaffolds were used as templates for the construction of a virtual library of 11 748 compounds employing 44 indoles, 12 aldehydes, and 51 alkynes. Diversity analyses using a combination of cell-based chemistry space computations using BCUT (Burden (B) CAS (C) Pearlman at the University of Texas (UT)) metrics and Tanimoto coefficient (Tc) similarity calculations using two-dimensional (2D) fingerprints showed that the compounds in the virtual library occupied new chemical space when compared to the 327,000 compounds in the molecular libraries small molecule repository (MLSMR). A subset of fifty-three compounds was identified from the virtual library using the DVS package of Sybyl 8.0; this subset represents the most diverse compounds within the chemical space defined by these compounds and will be synthesized and screened for biological activity.

Synthesis and evaluation of new endomorphin analogues modified at the Pro(2) residue

Six new endomorphin analogues, incorporating constrained amino acids in place of native proline have been synthesized. Residues of (S)-azetidine-2-carboxylic acid (Aze), 3,4-dehydro-(S)-proline (Delta(3)Pro), azetidine-3-carboxylic acid (3Aze) and dehydro-alanine (DeltaAla) have been used to prepare [Delta(3)Pro(2)]EM-2 (1), [Aze(2)]EM-1 (2), [Aze(2)]EM-2 (3), [3Aze(2)]EM-1 (4), [3Aze(2)]EM-2 (5) and [DeltaAla(2)]EM-2 (6). Binding assays and functional bioactivities for mu- and delta-receptors are reported. The highest affinity, bioactivity and selectivity are shown by peptides 2 and 3 containing the Aze residue.

Lewis acid catalyzed [1,3]-sigmatropic rearrangement of vinyl aziridines

This paper details the copper-catalyzed ring expansion of vinyl aziridines to 3-pyrrolines. Broad substrate scope (24 examples) using tosyl- and phthalimide-protected vinyl aziridine substrates is observed. Cu(hfacac)2 was determined to be superior to all other catalysts tested.

Diverging Rh(I)-catalyzed carbocylization strategy to prepare a library of unique cyclic ethers

A library of 90 carboxamide-containing oxepines and pyrans was synthesized. A dual-branching strategy was used where a common intermediate, an allenyl-hydroxy ester, was either allylated or propargylated then subjected to rhodium(I)-catalyzed carbocyclization reaction conditions to afford an oxepine- or triene-containing pyran, respectively. The oxepines were selectively reduced to afford two functionally unique scaffolds using complementary hydrogenation conditions. Diversification of the oxepines and pyrans involved conversion of the methyl carboxylate group to a carboxamide via either a microwave-assisted amidation using polymer-bound carbodiimide (DCC) and 1-hydroxybenzotriazole (HOBt) or a NaCN-catalyzed aminolysis. The scope of a rarely used carbonyl-yne reaction was expanded to the preparation of 10 new allenyl-hydroxy esters using microwave irradiation. Finally, a cell-based diversity analysis using BCUT (Burden (B) CAS (C) Pearlman at the University of Texas (UT)) metrics calculations and two-dimensional fingerprint similarity approaches shows that when compared to the 100,000 Pittsburgh Molecular Library Screening Center (PMLSC) compound database and PubChem the new compound library occupies a unique chemical space.