Synthetic Building Blocks Research Articles

Divergent synthetic routes to biologically relevant types of compounds: chiral polyfunctional γ-lactams and amino acids

Divergent and versatile synthetic routes leading to the title compounds are described. They start from a common chiral precursor derived from (−)-(S)-verbenone and afford polyfunctional γ-lactams and γ- and ε-amino acids. The cyclobutane moiety in these molecules acts as a chiral and polyfunctional platform providing stereogenic centres with unambiguous absolute configuration that control the chirality of the newly produced asymmetric carbons. Furthermore, it affords functional groups and carbon chains suitable not only to create the basic skeleton of the desired products but additional functional groups. These features confer on these derivatives a great versatility for further uses in the development of new drugs and as synthetic building blocks.

ChemInform Abstract: Organocatalytic Enantioselective Vinylogous Michael Reaction of Vinylketene Silyl‐N,O‐acetals.

The enantioselective vinylogous Michael reaction of vinylketene silyl N,O-acetals derived from α,β-unsaturated N-acyl pyrroles and a broad range of α,β-unsaturated aldehydes proceeds with good regio-, diastereo-, and enantioselectivity when the Hayashi–Jorgensen diphenylprolinolsilylether was employed as a chiral organocatalyst. Products were obtained in generally good yields and as single stereoisomers after chromatographic purification with very high optical purity. They were easily derivatized into a set of useful synthetic building blocks.

ChemInform Abstract: A Journey from the Pool of Chiral Synthetic Building Blocks to Cell‐penetrating Peptides, to a Novel Type of Enzyme ‐ and Back.

The roles of polyhydroxy-butyrates/alkanoates (PHB/PHA) in biology, for the preparation of chiral building blocks, and as a source of inspiration for the discovery of β- and γ-peptides are discussed. The syntheses and structures of β-peptides are outlined. The prerequisites for mimicking peptide/protein interactions with β-peptides and two examples are presented. Single terminal β-amino-acid residues can lead to stabilization of peptides (cf. NTS(8-13)) in plasma. Cell-penetrating α-L-, α-D-, mixed α-L/D- and β-oligoarginines (OAs) and -oligoprolines, as well as the mechanism(s) of internalization are compared. Recent studies show that infected erythrocytes, parasitic organisms and mycobacteria are entered by OA-derivatives, which have been employed as transporters of the antibiotic fosmidomycin. While β-peptides are generally enzymatically stable (for days in mammals), a microorganism (S. xenopeptidilytica) with an Ntn enzyme (3-2W4 BapA) was discovered that cleaves only β-peptides, and that was applied in preparations of (enantiopure) β-amino acids and β-peptides.

Primary Structure Control of Oligomers Based on Natural and Synthetic Building Blocks.

Solid-phase synthesis was exploited for the preparation of oligomers constructed from natural and synthetic building blocks by combining the formation of amide bonds and copper-assisted alkyne-azide cycloaddition reactions extending the variety of oligomers with well-defined primary structures accessible through this technique and providing control over the spacing between amino acids.

Catalytic, Enantioselective Synthesis of 1,2‐anti‐Diols by Asymmetric Ring‐Opening/Cross‐Metathesis

AbstractAn enantioselective method for the synthesis of 1,2‐anti‐diols has been developed. A cyclometalated chiral‐at‐ruthenium complex catalyzes the asymmetric ring‐opening/cross‐metathesis of dioxygenated cyclobutenes, thus resulting in functionally rich synthetic building blocks. Syntheses of the insect pheromone (+)‐endo‐brevicomin and monosaccharide ribose demonstrate the synthetic utility of the 1,2‐anti‐diol fragments generated in the title reaction.

Catalytic, Enantioselective Synthesis of 1,2‐anti‐Diols by Asymmetric Ring‐Opening/Cross‐Metathesis

An enantioselective method for the synthesis of 1,2-anti-diols has been developed. A cyclometalated chiral-at-ruthenium complex catalyzes the asymmetric ring-opening/cross-metathesis of dioxygenated cyclobutenes, thus resulting in functionally rich synthetic building blocks. Syntheses of the insect pheromone (+)-endo-brevicomin and monosaccharide ribose demonstrate the synthetic utility of the 1,2-anti-diol fragments generated in the title reaction.

Fabrication of PEGylated fibrinogen: a versatile injectable hydrogel biomaterial.

Hydrogels are one of the most versatile biomaterials in use for tissue engineering and regenerative medicine. They are assembled from either natural or synthetic polymers, and their high water content gives these materials practical advantages in numerous biomedical applications. Semisynthetic hydrogels, such as those that combine synthetic and biological building blocks, have the added advantage of controlled bioactivity and material properties. In myocardial regeneration, injectable hydrogels premised on a semisynthetic design are advantageous both as bioactive bulking agents and as a delivery vehicle for controlled release of bioactive factors and/or cardiomyocytes. A new semisynthetic hydrogel based on PEGylated fibrinogen has been developed to address the many requirements of an injectable biomaterial in cardiac restoration. This chapter highlights the fundamental aspects of making this biomimetic hydrogel matrix for cardiac applications.

A Journey from the Pool of Chiral Synthetic Building Blocks to Cell-Penetrating Peptides, to a Novel Type of Enzyme – and back

The roles of polyhydroxy-butyrates/alkanoates (PHB/PHA) in biology, for the preparation of chiral building blocks, and as a source of inspiration for the discovery of β- and γ-peptides are discussed. The syntheses and structures of β-peptides are outlined. The prerequisites for mimicking peptide/protein interactions with β-peptides and two examples are presented. Single terminal β-amino-acid residues can lead to stabilization of peptides (cf. NTS(8-13)) in plasma. Cell-penetrating α-L-, α-D-, mixed α-L/D- and β-oligoarginines (OAs) and -oligoprolines, as well as the mechanism(s) of internalization are compared. Recent studies show that infected erythrocytes, parasitic organisms and mycobacteria are entered by OA-derivatives, which have been employed as transporters of the antibiotic fosmidomycin. While β-peptides are generally enzymatically stable (for days in mammals), a microorganism (S. xenopeptidilytica) with an Ntn enzyme (3-2W4 BapA) was discovered that cleaves only β-peptides, and that was applied in preparations of (enantiopure) β-amino acids and β-peptides.

Organocatalytic Enantioselective Vinylogous Michael Reaction of Vinylketene Silyl-N,O-Acetals

The enantioselective vinylogous Michael reaction of vinylketene silyl N,O-acetals derived from α,β-unsaturated N-acyl pyrroles and a broad range of α,β-unsaturated aldehydes proceeds with good regio-, diastereo-, and enantioselectivity when the Hayashi-Jørgensen diphenylprolinolsilylether was employed as a chiral organocatalyst. Products were obtained in generally good yields and as single stereoisomers after chromatographic purification with very high optical purity. They were easily derivatized into a set of useful synthetic building blocks.

Cell Surface Self-Assembly of Hybrid Nanoconjugates via Oligonucleotide Hybridization Induces Apoptosis

Hybrid nanomaterials composed of synthetic and biological building blocks possess high potential for the design of nanomedicines. The use of self-assembling nanomaterials as "bio-mimics" may trigger cellular events and result in new therapeutic effects. Motivated by this rationale, we designed a therapeutic platform that mimics the mechanism of immune effector cells to cross-link surface receptors of target cells and induce apoptosis. This platform was tested against B-cell lymphomas that highly express the surface antigen CD20. Here, two nanoconjugates were synthesized: (1) an anti-CD20 Fab' fragment covalently linked to a single-stranded morpholino oligonucleotide (MORF1), and (2) a linear polymer of N-(2-hydroxypropyl)methacrylamide (HPMA) grafted with multiple copies of the complementary oligonucleotide MORF2. We show that the two conjugates self-assemble via MORF1-MORF2 hybridization at the surface of CD20(+) malignant B-cells, which cross-links CD20 antigens and initiates apoptosis. When tested in a murine model of human non-Hodgkin's lymphoma, the two conjugates, either administered consecutively or as a premixture, eradicated cancer cells and produced long-term survivors. The designed therapeutics contains no small-molecule cytotoxic compounds and is immune-independent, aiming to improve over chemotherapy, radiotherapy and immunotherapy. This therapeutic platform can be applied to cross-link any noninternalizing receptor and potentially treat other diseases.

Ynamides in Ring Forming Transformations

The ynamide functional group activates carbon-carbontriple bonds through an attached nitrogen atom that bears an electron-withdrawing group. As a result, the alkyne has both electrophilic and nucleophilic properties. Through the selection of the electron-withdrawing group attached to nitrogen, chemists can modulate the electronic properties and reactivity of ynamides, making these groups versatile synthetic building blocks. The reactions of ynamides also lead directly to nitrogen-containing products, which provides access to important structural motifs found in natural products and molecules of medicinal interest. Therefore, researchers have invested increasing time and research in the chemistry of ynamides in recent years. This Account surveys and assesses new organic transforma-tions involving ynamides developed in our laboratory and in others around the world. We showcase the synthetic power of ynamides for rapid assembly of complex molecular structures. Among the recent reports of ynamide transformations, ring-forming reactions provide a powerful tool for generating molecular complexity quickly. In addition to their synthetic utility, such reactions are mechanistically interesting. Therefore, we focus primarily on the cyclization chemistry of ynamides. This Account highlights ynamide reactions that are useful in the rapid synthesis of cyclic and polycyclic structural manifolds. We discuss the mechanisms active in the ring formations and describe representative examples that demonstrate the scope of these reactions and provide mechanistic insights. In this discussion, we feature examples of ynamide reactions involving radical cyclizations, ring-closing metathesis, transition metal and non-transition metal mediated cyclizations, cycloaddition reactions, and rearrangements. The transformations presented rapidly introduce structural complexity and include nitrogen within or in close proximity to a newly formed ring (or rings). Thus, ynamides have emerged as powerful synthons for nitrogen-containing heterocycles and nitrogen-substituted rings, and we hope this Account will promote continued interest in the chemistry of ynamides.

Improved Synthesis of Cyclic Tertiary Allylic Alcohols by Asymmetric 1,2‐Addition of AlMe3 to Enones

The development of an improved protocol for the enantioselective Rh(I) /binap-catalysed 1,2-addition of AlMe3 to cyclic enones is reported. (31)P NMR analysis of the reaction revealed that the catalyst in its resting state is a chloride-bridged dimer. This insight led to the use of AgBF4 as an additive for in situ activation of the dimeric precatalyst. Thus, the catalyst loading can now be reduced to only 1 mol% with respect to rhodium. Various 5-7-membered cyclic enones can be transformed into tertiary allylic alcohols with excellent levels of enantioselectivity and high yields. The obtained products are versatile synthetic building blocks, shown by a highly enantioselective formal total synthesis of the pheromone (-)-frontalin as well as formation of a bicyclic lactone that has the core structure of the natural flavour component "wine lactone".

Synthesis of 10-methyl-8,10-diazabicyclo[4.3.1]decane as a new building block for nicotinic modulators

A convenient method for the synthesis of 10-methyl- 8,10-diazabicyclo[4.3.1]decane, possessing a novel diazabicyclic ring system, as an important synthetic organic chemistry building block was developed using octanedioic acid as a starting material. The key transformation in the 5-step synthesis sequence involved a reaction of dimethyl 2,7-dibromooctanoate with methylamine, which resulted in the formation of cis -dimethyl 1-methylazepan-2,7-dicarboxylate. The lat ter was further transformed into bicyclic 8-benzyl-10-m ethyl-8,10-diazabicyclo[4.3.1]decane-7,9dione under heating with benzylamine. Reduction of the formed bicyclic dione with lithium aluminium hydride resulted in 8-benzyl-10-methyl-8,10-diazabicyclo[4.3.1]decane, and hydrogenolysis efficiently yielded the target produ ct.

Self‐assembly in nature: using the principles of nature to create complex nanobiomaterials

Self-assembly is a ubiquitous process in biology where it plays numerous important roles and underlies the formation of a wide variety of complex biological structures. Over the past two decades, materials scientists have aspired to exploit nature's assembly principles to create artificial materials, with hierarchical structures and tailored properties, for the fabrication of functional devices. Toward this goal, both biological and synthetic building blocks have been subject of extensive research in self-assembly. In fact, molecular self-assembly is becoming increasingly important for the fabrication of biomaterials because it offers a great platform for constructing materials with high level of precision and complexity, integrating order and dynamics, to achieve functions such as stimuli-responsiveness, adaptation, recognition, transport, and catalysis. The importance of peptide self-assembling building blocks has been recognized in the last years, as demonstrated by the literature available on the topic. The simple structure of peptides, as well as their facile synthesis, makes peptides an excellent family of structural units for the bottom-up fabrication of complex nanobiomaterials. Additionally, peptides offer a great diversity of biochemical (specificity, intrinsic bioactivity, biodegradability) and physical (small size, conformation) properties to form self-assembled structures with different molecular configurations. The motivation of this review is to provide an overview on the design principles for peptide self-assembly and to illustrate how these principles have been applied to manipulate their self-assembly across the scales. Applications of self-assembling peptides as nanobiomaterials, including carriers for drug delivery, hydrogels for cell culture and tissue repair are also described.

Synthesis of a bisphosphonate derivative of folic acid

1-Amino-1,1-bisphosphonates are attracting heightened attention in various sectors of chemistry and medicine owing to a combination of unique chemical, physical, and biological properties. The combination of these properties opens possibilities for molecular design and synthesis of various biologically active compounds that are used as immunomodulators, calciumexchange regulators, and antitumor drugs [1]. Complex conjugates of bisphosphonates and natural biologically active compounds have recently become interesting. Thus, bisphosphonates based on widely known antibiotics of the fluoroquinolone series [2] and the folic-acid antagonist methotrexate, which is used to treat neoplastic diseases [3], were synthesized. Targeted delivery of drugs through covalent binding of carboxymethylchitosan nanoparticles and folic acid was recently found to be possible. It was assumed that the latter would assist penetration of the nanoparticle into the cell and cause its apoptosis [4]. The present communication reports the synthesis of the conjugate of a bisphosphonate derivative and folic acid. A one-step synthesis using the structural synthetic building block 1-(2-aminoethylamino)-1-(diethylphosphoryl)ethylphosphonic acid diethyl ester (2) was proposed for modifying folic acid. Compound 2 was obtained in 45% yield by phosphorylation of N-(2-aminoethyl)acetamide (1) (2.2 g, 22 mmol) by analogy with the literature method [5]. The reaction of folic acid (3) (0.20 g, 0.45 mmol) and 2 (0.19 g, 0.53 mmol) in the presence of dicyclohexylcarbodiimide (0.28 g, 1.36 mmol) was carried out according to the literature method [4]. The yield of 2-{4-[(2-amino-4-hydroxypteridin-6-ylmethyl)-amino]-benzamido}5-{2-[1,1-bis-(diethylphosphoryl)-ethylamino]-ethylamino}-5-oxopentanoic acid (4) was 20%. The structure of the product was confirmed using PMR and 31 P NMR spectroscopy and mass spectrometry. Thus, the first bisphosphonate derivative of folic acid was synthesized.

ChemInform Abstract: Supramolecular Chemical Biology; Bioactive Synthetic Self‐Assemblies

AbstractReview: 120 refs.

Allenamides: a powerful and versatile building block in organic synthesis.

Allenamides: a powerful and versatile building block in organic synthesis.

Organic Preparations with Molar Amounts of Volatile Malodorous Thiols

Thiols are indispensable for the preparation of many organic sulfur compounds. Their strong smell and use for gas leakage perception render it almost impossible to work with them without arousing public attention. Molar amounts of the very odoriferous thiol 2-methyl-2-propanethiol (t-butylthiol) are needed, for example, for the large-scale synthesis of two useful synthetic building blocks, 1,2,4,5-tetrakis(t-butylthio)benzene and tetramethylbenzo-2,2,6,6-[1,2-d;4,5-d']bis[1,3]dithiol. We investigated an array of alternatives to circumvent the problem: (1) alternative thiols (primary, long-chain, tertiary thiols of larger molar mass); (2) exhaust cleaning methods (adsorption, oxidation, conversion to a salt); and (3) thermal exhaust treatment. Only combustion of the fumehood exhaust with domestic gas at 900 °C in a regenerative thermal oxidation unit was able to completely prevent the thiol smell from escaping. Supplemental materials are available for this article. Go to the publisher's online edition of Synthetic Communications® to view the free supplemental file.

Synthesis of cis-2-alkoxycyclopropylamines via intramolecular cyclization of 2-azaallylic anions derived from alkoxybrominated N-(arylidene)-2-methyl-2-propenylamines

N-(Arylidene)-2-alkoxy-3-bromo-2-methylpropylamines, obtained in a straightforward way via regiospecific alkoxybromination of the corresponding N-(2-methyl-2-propenyl)imines, represent promising densely functionalized synthetic building blocks. The substituted N-(3-bromopropyl)imines were deprotonated to the corresponding 2-azaallylic anions, which underwent a highly diastereoselective intramolecular ring closure to new cis-N-(arylidene)-2-alkoxy-2-methylcyclopropylamines (cis:trans up to 99:1) in good to excellent yields (62–95%). These cis-cyclopropylamines proved to be excellent precursors of new conformationally constrained β-amino ethers.

Asymmetric routes to pentadec-1-en-4-ol: application to the syntheses of aculeatins F and epi-F, (R)- and (S)-5-hexadecanolide and a formal synthesis of solenopsin

Abstract A short and simple route to the synthesis of pentadec-1-en-4-ol, an important synthetic building block for the aculeatins F and epi -F, insect pheromone 5-hexadecanolide, solenopsin and various other natural products has been developed via proline-catalyzed α-aminoxylation of an aldehyde and hydrolytic kinetic resolution of a terminal epoxide. While the synthesis of aculeatins F and epi -F has been accomplished using a PIFA promoted oxidative spirocyclization/dithiane deprotection reaction sequence and linchpin coupling as key steps, the synthesis of hexadecanolide and a formal synthesis of solenopsin was performed using ring-closing metathesis (RCM) as key step.