Parallel synthesis of a vitamin D(3) library in the solid-phase.

A highly efficient synthesis of the vitamin D(3) system on solid support is described. Two synthetic strategies for the solid-phase synthesis of vitamin D(3) were developed. One is for 11-hydroxy analogues, and the other is for most other synthetic analogues. In the latter strategy, the sulfonate-linked CD-ring 58 was initially immobilized on PS-DES resin to give solid-supported CD-ring 63 (Scheme 10). Similarly, solid-supported CD-ring 63 was prepared by attachment of the CD-ring 10 to the chlorosulfonate resin 64. The vitamin D(3) system was synthesized by Horner-Wadsworth-Emmons reaction of the A-ring phosphine oxide to a solid-supported CD-ring, followed by simultaneous introduction of the side chain and cleavage from resin with a Cu(I)-catalyzed Grignard reagent. Parallel synthesis of the vitamin D(3) analogues was accomplished by a split and pool methodology utilizing radio frequency encoded combinatorial chemistry, and a manual parallel synthesizer for side chain diversification and deprotection. Additionally, we demonstrated the synthesis of various A-rings in a similar protocol for efficient preparation of building blocks.     

Synthesis of 8-(S)-methoxy-11-desmethyl laulimalide: a novel laulimalide analogue

A strategy is outlined which enables preparation of novel laulimalide analogues at C.8 and C.11. A representative analogue, 8-(S)-methoxy-11-desmethyl laulimalide, was synthesized via this route.     

Synthesis and biological evaluation of (-)-laulimalide analogues

[reaction: see text] The syntheses of five laulimalide analogues are described, incorporating modifications at the C(16)-C(17)-epoxide, the C(20)-alcohol, as well as the C(1)-C(3)-enoate of the parent natural product. The resultant analogues are active in drug-sensitive HeLa and MDA-MB-435 cell lines. Significantly, like laulimalide, these analogues are poor substrates for the drug transport protein P-glycoprotein (Pgp) and are thus effective against Taxol-resistant cell lines.     

Synthesis of novel 11-desmethyl analogues of laulimalide by Nozaki-Kishi coupling

As a first entry into structurally simplified analogues of the anticancer agent laulimalide, 11-desmethyl compounds 2 and 3 were selected by molecular modeling. The unfavorable diastereoselectivity in the key synthetic step, a Nozaki-Kishi coupling between macrocyclic aldehyde 4 and vinyl iodide 5, was overcome either by use of catalytic amounts of DIANANE-type ligands or L-Selectride reduction of the derived enone. This methodology should allow modular introduction of other, unnatural, side chains. [reaction: see text]     

Total synthesis of laulimalide: assembly of the fragments and completion of the synthesis of the natural product and a potent analogue

Herein, we present a full account of our efforts to couple the northern and the southern building blocks, the synthesis of which were described in the preceding paper, along with the modifications required to ultimately lead to a successful synthesis of laulimalide. Key highlights include an exceptionally efficient and atom-economical intramolecular ruthenium-catalyzed alkene-alkyne coupling to build the macrocycle, followed by a highly stereoselective 1,3-allylic isomerization promoted by a rhenium complex. Interestingly, the designed synthetic route also allowed us to prepare an analogue of the natural product that possesses significant cytotoxic activity. We also report a second generation route that provides a more concise synthesis of the natural product.     

Synthesis and PKC binding of a new class of a-ring diversifiable bryostatin analogues utilizing a double asymmetric hydrogenation and cross-coupling strategy

The design, asymmetric synthesis, and biological evaluation of a new class of bryostatin analogues based on a pseudosymmetric spacer domain are described. An aryl bromide diversification site is incorporated allowing access to systematically varied analogues. The new analogues all exhibit potent, nanomolar affinity to PKC.     

Strategies for the solid-phase diversification of poly-L-proline-type II peptide mimic scaffolds and peptide scaffolds through guanidinylation

A strategy for the solid-phase diversification of PPII mimic scaffolds through guanidinylation is presented. The approach involves the synthesis N-Pmc-N'-alkyl thioureas as diversification reagents. Analogues of Fmoc-Orn(Mtt)-OH can be incorporated into a growing peptide chain on Wang resin. Side chain deprotection with 1% TFA/CH2Cl2 followed by EDCI-mediated reaction of N-Pmc-N'-alkyl thioureas with the side chain amine affords arginine analogues with modified guanidine head groups. The scope, limitations, and incidental chemistry are discussed.     

A novel methodology for the synthesis of 1-desoxy-Δ-tetrahydrocannabinol (THC) analogues

A versatile and efficient sequence was developed for the synthesis of 1-desoxy-Δ⁸-THC analogues and is demonstrated by the synthesis of sulfonamide analogues with an acetylene group at the C-2^′ position in the side chain. In this procedure the 1-desoxy-Δ⁸- THC ring structure is built first and the synthesis of the side chain is then developed.     

Synthesis of gramicidin S and its analogues via an on-resin macrolactamization assisted by a predisposed conformation of the linear precursors

A simple and efficient preparation of gramicidin S and its analogues is described. It involves solid-phase peptide synthesis and on-resin macrolactamization without side chain protection, affording cyclic products in high yield and high purity. The high specificity of the cyclization reaction was shown to originate in the formation of a pre-organized conformation of the linear biosynthetic precursor of gramicidin S. This facile method will provide convenient access to the analogues of the natural product for functional optimization to counter microbial resistance.     

Method for the solid-phase parallel synthesis of a 6-alkylamino-2-(functionalized-aminomethyl)-2H-1-benzopyran Library

A 2000-member library of benzopyran analogues was prepared by using a solid-phase synthesis protocol. Polymer-bound 6-alkylaminobenzopyrans 7 were synthesized as part of a first generation diversification step by employing reactions of a variety of alkyl halides with the amine 6. Transformations of the resin-bound intermediates 8 formed in this manner by reactions with acid halides, sulfonyl chlorides, and isocyanates leads to introduction of the second level of diversification found in the series of 6-alkylamino-2-(functionalized-aminomethyl)-2-methyl-2H-1-benzopyran analogues 11 and 12.     

The thioacetate approach to the synthesis of the side chain of vitamin D metabolites and analogues

We describe an efficient synthesis of thia analogues of the vitamin D side chain that is based on the in situ generation of a thiolate anion and its alkylation with electrophiles.     

Synthesis and biological evaluation of a des-dihydropyran laulimalide analog

The preparation of a novel simplified Laulimalide analog via a highly convergent and efficient route and its biological evaluation are presented. The outlined route enables the synthesis of C₅–C₉ modified analog 2 and uses Julia–Kocienski olefination for fragment assembly and a regioselective Yamaguchi macrolactonization for ring closure. This strategy should be suitable for the generation of various new C₅–C₉ des-dihydropyran laulimalide derivatives for further SAR studies.     

Conformational studies and solution structure of laulimalide and simplified analogues using NMR spectroscopy and molecular modelling

The solution structures of the potent microtubule-stabilizing anti-cancer agent laulimalide and simplified analogues were determined by a combination of high field ¹H NMR spectroscopic studies (J-based configuration analysis and NOESY) and constrained molecular dynamics simulations and discussed in relation to their antiproliferative activity.     

Construction of a 2,6-difunctionalized 2-methyl-2H-1-benzopyran library by using a solid-phase synthesis protocol

[reaction: see text] A library containing 1200 analogues of 2,6-difunctionalized 2-methyl-2H-1-benzopyran was constructed by using a solid-phase synthesis protocol. Polymer-bound 6-amido-, 6-sulfonamido-, and 6-uredo-functionalized 2-hydroxymethyl-2-methylbenzopyrans 10 were prepared as part of a first-generation diversification step by employing reactions of respective acid halides, sulfonyl chlorides, and isocyanates with the amine precursor 7. Transformations of the resin-bound intermediates 10 by reactions with alkyl and acid halides were then used to produce a diverse series of 2,6-difunctionalized 2-methyl-2H-1-benzopyran analogues 12 and 14.     

Function-Oriented and Modular (+/−)-cis-Pseudoguaianolide Synthesis: Discovery of New Nrf2 Activators and NF-κB Inhibitors

Described herein is a function-oriented synthesis route and biological evaluation of pseudoguaianolide analogues. The 10-step synthetic route developed retains the topological complexity of the natural product, installs functional handles for late-stage diversification, and forges the key bioactive Michael acceptors early in the synthesis. The analogues were found to be low-micromolar Nrf2 activators and micromolar NF-κB inhibitors and dependent on the local environment of the Michael acceptor moieties.     

The Laulimalide Family: Total Synthesis and Biological Evaluation of Neolaulimalide,Isolaulimalide, Laulimalide and a Nonnatural Analogue

A sensitive family : The first total synthesis of the antitumor agents neolaulimalide and isolaulimalide as well as a highly efficient route to laulimalide is described. A Kulinkovich reaction followed by a cyclopropyl–allyl rearrangement is used to install the exo‐methylene group. The cytotoxicity of neolaulimalide could be confirmed for the first time since its original isolation and it could be shown that it induces tubulin polymerization as efficiently as laulimalide.

     

Separation of Arylenevinylene Macrocycles with a Surface‐Confined Two‐Dimensional Covalent Organic Framework

A two‐dimensional surface covalent organic framework, prepared by a surface‐confined synthesis using 4,4′‐azodianiline and benzene‐1,3,5‐tricarbaldehyde as the precursors, was used as a host network to effectively immobilize arylenevinylene macrocycles (AVMs). Thus AVMs could be separated from their linear polymer analogues, which are the common side‐products in the cyclooligomerization process. Scanning tunneling microscopy investigations revealed efficient removal of linear polymers by a simple surface binding and solvent washing process.     

Solid-phase synthesis of N-nosyl- and N-Fmoc-N-methyl-alpha-amino acids

We report here a convenient and simple solid-phase synthesis of N-nosyl-N-methyl-alpha-amino acids and N-Fmoc-N-methyl-alpha-amino acids, important building blocks for the synthesis of conformationally restricted and protease-resistant natural peptides and peptide analogues. The methodology involves the use of 2-chlorotrityl chloride resin to temporarily protect the carboxylic group of alpha-amino acids and of diazomethane as the reagent to methylate the sulfonamidic function. The approach developed is particularly efficient also with alpha-amino acids bearing appropriately protected functionalized side chains.     

Total synthesis and biological evaluation of 11-desmethyllaulimalide, a highly potent simplified laulimalide analogue

[reaction: see text] A step-economical synthesis of 11-desmethyllaulimalide (2) is reported. This simplified analogue is available through an improved second-generation synthetic approach to the laulimalides, in a shorter step count and from much less expensive starting material than the parent compound. This new lead retains the anticancer function of laulimalide.     

Solid-phase synthesis of dihydrovirginiamycin S1, a streptogramin B antibiotic

We describe the first solid-phase synthesis of dihydrovirginiamycin S(1), a member of the streptogramin B family of antibiotics, which are nonribosomal-peptide natural products produced by Streptomyces. These compounds, along with the synergistic group A components, are "last line of defense" antimicrobial agents for the treatment of life-threatening infections such as vancomycin-resistant enterococci. The synthesis features an on-resin cyclization and is designed to allow production of streptogramin B analogues with diversification at positions 1', 1, 2, 3, 4, and 6. Several synthetic challenges known to hinder the synthesis of this class of compounds were solved, including sensitivity to acids and bases, and epimerization and rearrangements, through the judicious choice of deprotection conditions, coupling conditions, and synthetic strategy. This work should enable a better understanding of structure-activity relationships in the streptogramin B compounds, possible identification of analogues that bypass known resistance mechanisms, and perhaps the identification of analogues with novel biological activities.