Facile syntheses of conformationally constrained analogues of lysine and homoglutamic acid

A facile divergent synthesis of the novel amino acid trans-4-aminoethyl-l-proline and trans-4-carboxymethyl-l-proline from commercially available trans-4-hydroxy-l-proline was developed. These conformationally constrained analogues of l-lysine and l-homoglutamic acid are useful proline templated amino acids (PTAAs) with potential applications in protein engineering and de novo protein design.     

Synthesis of conformationally constrained spirodihydrofuropyridine analogues of epibatidine

Conformationally constrained spirofuropyridine analogues of epibatidine, syn-2 and anti-2, in which the 7-azabicyclo[2.2.1]heptane system and the 2-chloropyridine ring are held rigidly with the shorter and longer N-N distances, respectively, were synthesized from N-Boc-7-azabicyclo[2.2.1]heptan-2-one. The preliminary binding studies suggested that syn-2 has stronger binding affinity for nAChRs than anti-2.     

Synthesis of conformationally constrained analogues of RGD tripeptide

Convergent syntheses of N-functionalized (3S,4S)-3-amino-4-vinyl-piperidin-2-one 10, trans-3-substituted proline 18 and (3S)-3-amino-piperidin-2-one 28 are developed. By incorporating these building blocks to an appropriate position, conformationally constrained analogues of RGD tripeptide (Arg-Gly-Asp) 2, 3 and 4 are designed and synthesized.     

Synthesis and chromatographic resolution of conformationally constrained analogues of homotaurine

The first series of conformationally constrained analogues of homotaurine is reported. The partial constriction of the skeleton was realized through the insertion of a cyclopropyl ring, between the α,β- and β,γ-positions, thus affording, respectively, trans- and cis-2-aminomethylcyclopropane-1-sulfonic acids and trans- and cis-(2-aminocyclopropyl)methanesulfonic acids. The resolution of all four racemic mixtures was accomplished using HPLC system carrying the polysaccharide-based Chiralpak^® IB^® column as the chiral stationary phase. The coupling with an ‘Evaporative Light Scattering Detector (ELSD)’ has been particularly valuable during the chromatographic study.     

Synthesis of two conformationally constrained analogues of the minor tobacco alkaloid anabasine

The anabasine analogues spiro[4-azaindan-1,2'-piperidine] (7) and spiro[6-azaindan-1,2'-piperidine] (8) have been prepared. A series of palladium-catalyzed reactions, where an intramolecular cyclization constituted a key reaction, were utilized for the preparation of the two target compounds.     

Synthesis of functionally diverse and conformationally constrained polycyclic analogues of proline and prolinol

Alkylation of the monoenolate of N-Boc-l-pyroglutamic acid methyl ester with a variety of benzylic halides and their homologues gave the corresponding anti-C-4-alkylated products as major products. Formation of the N-Boc-iminium ion and Friedel-Crafts intramolecular cationic ring closure afforded a series of fused 1-azacyclodihydroindene derivatives with interesting topologies. Functional diversity was introduced via further manipulation of pendant groups on the original proline motif as well as on the aromatic moiety.     

Synthesis of 5-substituted pipecolic acid derivatives as new conformationally constrained ornithine and arginine analogues

Two, orthogonally protected, constrained analogues of arginine have been synthesised in a diastereodivergent manner. The key step involved an electrophilic or radical functionalisation of methyl N-Boc-5,6-dehydropipecolate.     

Stereoselective synthesis of conformationally constrained omega-amino acid analogues from pyroglutamic acid

Bicyclic lactams derived from pyroglutamic acid provide a useful scaffold for synthesis of conformationally restricted analogues of lysine, ornithine and glutamine, as well as an Ala-Ala dipeptide analogue. Amino alcohol and carboxylic acid derivatives are accessible from a common intermediate. In this strategy, the bicyclic lactam system not only controls, but also facilitates the determination of the stereochemistry of the synthetic intermediates.     

Synthesis of conformationally locked versions of puromycin analogues

Conformationally locked North and South versions of puromycin analogues built on a bicyclo[3.1.0]hexane pseudosugar template were synthesized. The final assembly of the products was accomplished by the Staudinger-Vilarrasa coupling of the corresponding North (2 and 3) and South (6 and 7) 3'-azidopurine carbanucleosides with the Fmoc-protected 1-hydroxybenzotriazole ester of 4-methoxy-L-tyrosine. North azides 2 and 3 were reported earlier. The 3'-azido intermediates 6 and 7 that are necessary for the synthesis of the South puromycin analogues are described herein for the first time.     

Asymmetric synthesis of 4-substituted prolines as conformationally constrained amino acid analogues

Treatment of readily available chiral building block 1 with (2R)-2,3-O-isopropylideneglyceraldehyde (5) provides a new route for asymmetric synthesis of 2,4-disubstituted pyrrolidines. Several proline-amino acid chimeras: proline-leucine, proline-lysine, proline-arginine and proline-glutamic acid, are synthesized in highly diastereomerically pure forms.     

2-Oxopiperazine-based gamma-turn conformationally constrained peptides: synthesis of CCK-4 analogues

2-Oxopiperazine derivatives 1 have been designed as mimetics of gamma-turn conformationally constrained tripeptides. The synthetic pathway devised for the preparation of both epimers of 1 at C(5) involves a reductive amination of cyanomethyleneamino pseudopeptides with amino acid derivatives, followed by regiospecific lactamization of the resulting C-backbone branched pseudopeptides. The versatility of this methodology is illustrated in the synthesis of analogues of the tetrapeptides Boc-[Nle(31)]-CCK-4 and Boc-[Lys(o-tolylaminocarbonyl)(31)]-CCK-4. The introduction of the new conformational restriction into these Boc-CCK-4 analogues led to a loss of 2 or 3 orders of magnitude in the affinity at CCK receptors. These results suggest the absence of a gamma-turn in the bioactive conformation of the C-terminal tripeptide of CCK-4.     

Synthesis of conformationally constrained benzoylureas as BH3-mimetics

The design of small molecules that mimic the BH3 domain and bind to Bcl-2 proteins has emerged as a promising approach to discovering novel anti-cancer therapeutics. We reveal the design and synthesis of conformationally constrained benzoylurea scaffolds as conformational probes. Central to helix mimicry, the intramolecular hydrogen bond in the benzoylurea plays a key role in the pre-organisation of the acyclic substrates for cyclisation via ring closing metathesis, providing efficient access to the constrained mimetics.     

Synthesis of conformationally constrained adamantane imidazolines with trypanocidal activity

Aiming at the development of new adamantano building blocks for treating African trypanosomiasis, we report on the synthesis of spiro adamantane 2‐imidazolines 8a‐f and 9a‐c , and their congeneric 5‐(1‐adamantyl)imidazolines 14 and 15 . The potency of these compounds against Trypanosoma brucei was compared to that of rimantadine and found, in the case of compound 14e , to be three fold higher. Together with the other active compounds, 14b and 15b , which were equipotent to rimantadine, the new molecules illustrate the synergistic effect of the lipophilic character of adamantane and the C1 amidine functionality on trypanocidal activity.     

Synthesis of a new conformationally constrained glycoamino acid building block

The synthesis of a suitably protected β-d-glucopyranosyl-(S)-α-methylserine derivative—a new conformationally constrained glycosylated quaternary amino acid analogue of β-d-glucopyranosyl-l-serine—is described. This compound can be used as an attractive building block for the synthesis of new, constrained glycopeptides.     

Synthesis and biological activities of conformationally restricted cyclopentenyl-glutamate analogues.

An efficient method for preparing conformationally restricted cyclopentenyl-glutamate analogues in a regioselective and diastereoselective manner has been developed using a formal [3 + 2] cycloaddition reaction of dehydroamino acids. Methods for preparing optically active versions of these compounds have also been devised. Of these compounds, (S)-2 is an agonist at the mGlu5 (EC(50) 18 microM) and mGlu2 (EC(50) 45 microM) receptors.     

Synthesis of B2,5 type conformationally constrained glucopyranosides

Isopropyl and p-nitrophenyl α- and β-d-glucopyranosides restrained in a conformation close to B_2,5 have been synthesized. They are all hydrolyzed at similar rates, close to those observed for the parent unlocked glucosides.     

Synthesis of a new stable conformationally constrained 2,7-anhydrosialic acid derivative

A stereoseletive synthesis of 2,7-anhydrosialic acid derivative 18 was achieved from d-glucono-delta-lactone. A highly syn-selective addition of Grignard reagent to theN-benzylimine 8 served as a key step.     

Synthesis of conformationally constrained cyclic peptides using an intramolecular sonogashira coupling

[Reaction: see text]. Small peptides having a 3-bromobenzyl group at the C-termini and n-alkynoyl group at the N-termini undergo a smooth copper-free intramolecular Sonogashira coupling reaction to afford the corresponding cyclic peptides in moderate yields. Scope and limitations of this macrocyclization is demonstrated with di-, tri-, and tetrapeptides.     

Constructing conformationally constrained macrobicyclic musks

To investigate the structure-odor correlation of musks, (12R)-12-methyl-13-tridecanolide (1), a macrocyclic musk, and 13-tridecanolide, its non-musky demethyl analogue, were conformationally constrained by introduction of methylene bridges between C-3 and C-8 or C-9. These [7.5.1]- and [8.4.1]-macrobicycles were synthesized starting from bicyclo[5.3.1]undec-8-en-9-one (3) and bicyclo[4.3.1]dec-7-en-8-one (8), respectively, by a sequence consisting of catalytic hydrogenation, alpha-alkylation with a TBS-protected (tert-butyldimethylsilyl) hydroxy halide, acid-catalyzed cyclization, oxidative cleavage of the formed enol ether double bond, and subsequent reduction of the carbonyl group via its tosylhydrazone. The compound (1R,6R,9R)-(+)-6-methyl-4-oxa-bicyclo[7.5.1]pentadecan-3-one (22) was found to possess the most pronounced musk odor, and this was rationalized by a superposition analysis with the polycyclic aromatic musk odorant (4S,7R)-Galaxolide (2). In its (1S,6R,9S)-(+)-stereoisomer 23 as well as in (1S,6R, 10R)-(+)-6-methyl-4-oxabicyclo[8.4.1]-pentadecan-3-one (18) the (6R)-methyl group seems to hinder the interaction with the musk receptor, while the demethyl compounds 7 and 12 showed only very faint odors.