The asymmetric synthesis of (2 S ,3 R )-capreomycidine

Synthesis of pyrimidine-containing alkaloids

This review deals with the synthesis of naturally occurring alkaloids containing partially or completely saturated pyrimidine nuclei. The interest in these compounds is associated with their structural diversity, high biological activity and toxicity. The review is divided into four parts, each of which describes a number of synthetic methodologies toward structurally different naturally occurring alkaloids containing saturated cyclic six-membered amidine, guanidine, aminal and urea (thiourea) moieties, respectively. The development of various synthetic strategies for the preparation of these compounds has remarkably increased during the past few decades. This is primarily due to the fact that some of these compounds are isolated only in limited quantities, which makes it practically impossible to study their full structural characteristics and biological activity.

Stereocontrolled Total Synthesis of Muraymycin D1 Having a Dual Mode of Action against Mycobacterium tuberculosis

A stereocontrolled first total synthesis of muraymycin D1 (1) has been achieved. The synthetic route is highly stereoselective, featuring (1) selective β-ribosylation of the C2-methylated amino ribose, (2) selective Strecker reaction, and (3) ring-opening reaction of a diastereomeric mixture of a diaminolactone to synthesize muraymycidine (epi-capreomycidine). The acid-cleavable protecting groups for secondary alcohol and uridine ureido nitrogen are applied for simultaneous deprotections with the Boc and ^tBu groups. Muraymycin D1 (1) and its amide derivatives (2 and 3) exhibited growth inhibitory activity against Mycobacterium tuberculosis (MIC₅₀ = 1.56-6.25 μg/mL) and strong enzyme inhibitory activities against the bacterial phosphotransferases (MurX and WecA) (IC₅₀ = 0.096-0.69 μM).

Synthesis and bioactivity of antitubercular peptides and peptidomimetics: an update

This mini-review provides an update on the synthesis and bioactivity of peptides and peptidomimetics that exhibit very potent antitubercular activity.

A synthetic method to access symmetric and non-symmetric 2-(N,N'-disubstituted)guanidinebenzothiazoles

Symmetric and non-symmetric 2-(N-H, N-methyl, N-ethylenyl and N-aryl)guanidinebenzothiazoles were synthesized from the reaction of ammonia, methylamine, pyrrolidine and aniline with dimethyl benzo[d]thiazol-2-yl-carbonodithioimidate as intermediate. The products were characterized by ¹H-, ¹³C-NMR spectroscopy and three of them by X-ray diffraction analysis. HN-phenyl protons formed intramolecular hydrogen bonds that assist the stereochemistry of the second substituent, whereas the HN-alkyl protons were involved in intermolecular hydrogen bonding.

A biomimetic domino reaction for the concise synthesis of capreomycidine and epicapreomycidine

The non-proteinogenic amino acids capreomycidine and epicapreomycidine are constituents of antibiotically active natural products, but the synthesis of these unusual cyclic guanidine derivatives is challenging. The biosynthesis of capreomycidine has therefore been employed as a guideline to develop a concise biomimetic synthesis of both epimeric amino acids. The resulting domino-guanidinylation-aza-Michael-addition reaction provides the most convenient access to these amino acids in racemic form. Attempts to dissect the domino reaction into two separate transformations for a stereocontrolled version of this synthetic approach have also been made. The synthesized didehydro-arginine derivatives with urethane-protected guanidine moieties did not undergo the aza-Michael-addition anymore. These results may have wider implications for the 1,4-addition of guanidines to α,β-unsaturated carbonyl compounds, particularly to didehydro amino acids.

Synthesis of L-epi-capreomycidine derivatives via C-H amination

The L-epi-capreomycidine (Cpm) derivatives were efficiently and stereoselectively synthesized via nitrene C-H insertion starting from a readily available D-Tyr. Design of a substrate that takes into account hydrogen bonding is a critical feature in order to achieve high selectivity. Our synthetic strategy could be a new access to epi-Cpm and its derivatives, which are found in several biologically active natural products.

Natural products synthesis: enabling tools to penetrate Nature's secrets of biogenesis and biomechanism

Selected examples from our laboratory of how synthetic technology platforms developed for the total synthesis of several disparate families of natural products was harnessed to penetrate biomechanistic and/or biosynthetic queries is discussed. Unexpected discoveries of biomechanistic reactivity and/or penetrating the biogenesis of naturally occurring substances were made possible through access to substances available only through chemical synthesis. Hypothesis-driven total synthesis programs are emerging as very useful conceptual templates for penetrating and exploiting the inherent reactivity of biologically active natural substances. In many instances, new enabling synthetic technologies were required to be developed. The examples demonstrate the often untapped richness of complex molecule synthesis to provide powerful tools to understand, manipulate and exploit Nature's vast and creative palette of secondary metabolites.

Modular synthesis of non-peptidic bivalent NPY Y1 receptor antagonists

According to a 'bivalent ligand approach' to increase the affinity of the potent argininamide-type NPY Y(1) receptor antagonist BIBP-3226, dimeric ligands were synthesized in which two molecules of the parent compound were linked by different spacers via N(G)-acylation at the guanidino groups. A synthetic route for the preparation of the title compounds was developed, which includes a copper(I)-catalyzed azide alkyne cycloaddition as the key step. Three bivalent analogues of BIBP-3226 were prepared showing nanomolar antagonistic activity and binding affinity to the NPY Y(1) receptor (calcium assay on HEL cells, radioligand binding assay on SK-N-MC cells), but these ligands were not superior to the parent compound and there was no correlation with the length or the chemical nature of the spacer. A trivalent BIBP-3226 derivate showed, surprisingly, no affinity to the NPY Y(1) receptor at all.

An Easy Stereoselective Access to β,γ-Aziridino α-Amino Ester Derivatives via Mannich Reaction of Benzophenone Imines of Glycine Esters with N-Sulfonyl α-Chloroaldimines

Mannich-type addition of benzophenone imine glycinates across newly synthesized N-(p-toluenesulfonyl) alpha-chloroaldimines afforded gamma-chloro-alpha,beta-diamino ester derivatives with moderate diastereoselectivity as separable mixtures of anti and syn diastereomers. The gamma-chloro-alpha,beta-diamino esters were efficiently cyclized under basic conditions to the corresponding beta,gamma-aziridino alpha-amino ester derivatives, representing a new class of conformationally constrained heterocyclic alpha,beta-diamino acid derivatives. The relative configuration of the aziridines was determined via X-ray diffraction analysis. Mechanisms and intermediate transition states to explain the stereochemical outcome of the Mannich reaction with different substrates or under different conditions are proposed. The synthetic importance of the beta,gamma-aziridino alpha-amino ester derivatives is demonstrated by their conversion into the corresponding Boc-protected derivatives and ring opening reactions to alpha,beta-diamino esters and a gamma-amino alpha,beta-unsaturated amino ester.

New reagents, reactions, and peptidomimetics for drug design

It has been a major focus in our laboratories to prepare novel reagents and peptidomimetic structures for drug design. We have designed and prepared novel guanidinylation reagents that can be employed in solution or as solid phase reagents. We and others have utilized the reagent 3-(diethoxyphosphoryloxy)-1,2,3-benzotriazin-4(3H)-one (DEPBT) for amide bond formation to couple sterically hindered structures. These couplings proceed with remarkably strong resistance to racemization. In the area of peptidomimetics, we have incorporated novel building blocks to create biologically active compounds. These building blocks include thioether and alkylamine bridges, beta-methylated, and beta,beta-dimethylated amino acid residues. These mimetic structures have been incorporated into specific target molecules such as opioids to obtain cyclic peptidomimetics with potent and selective biological activity.