Preparation and Use of a General Solid-Phase Intermediate to Biomimetic Scaffolds and Peptide Condensations.

The Distributed Drug Discovery (D3) program develops simple, powerful, and reproducible procedures to enable the distributed synthesis of large numbers of potential drugs for neglected diseases. The synthetic protocols are solid-phase based and inspired by published work. One promising article reported that many biomimetic molecules based on diverse scaffolds with three or more sites of variable substitution can be synthesized in one or two steps from a common key aldehyde intermediate. This intermediate was prepared by the ozonolysis of a precursor functionalized at two variable sites, restricting their presence in the subsequently formed scaffolds to ozone compatible functional groups. To broaden the scope of the groups available at one of these variable sites, we developed a synthetic route to an alternative, orthogonally protected key intermediate that allows the incorporation of ozone sensitive groups after the ozonolysis step. The utility of this orthogonally protected intermediate is demonstrated in the synthesis of several representative biomimetic scaffolds containing ozonolytically labile functional groups. It is compatible with traditional Fmoc peptide chemistry, permitting it to incorporate peptide fragments for use in fragment condensations with peptides containing cysteine at the N-terminus. Overall yields for its synthesis and utilization (as many as 13 steps) indicate good conversions at each step.

Synthesis and crystal structure of anhydrous analog of 1,25-dihydroxyvitamin d3.

As predicted by single crystal X-ray crystallography, and contrary to the reported suggestions, the anhydrous form of calcipotriol, a therapeutically important vitamin D analog, was found stable enough to be used as an active pharmaceutical ingredient. The crystal and molecular structure of calcipotriol anhydrate was solved and refined using single crystal X-ray diffraction. The analog was obtained by a novel convergent synthesis from the vitamin D C-22 sulfone, as an advanced intermediate and a side-chain fragment. The homo-chiral side-chain aldehyde was obtained from cyclopropanecarboxyaldehyde by the chromatographic separation of the intermediate diastereomeric salts with (S)-naproxen. Calcipotriol anhydrate showed a single peak in differential scanning calorimetry and the absence of a peak from a water molecule, typical for the monohydrate. Calcipotriol anhydrate, as the only 1,25-dihydroxylated analog of vitamin D3 , exists as a mixture of both α- and ß-forms of the A-ring, present in the asymmetric part of the unit cell of the crystal lattice. The intermolecular hydrogen bonding between both conformers in the crystal lattice indicated that the stability of calcipotriol anhydrate might be at least the same as for the known monohydrate. The usefulness of calcipotriol anhydrate as an active pharmaceutical ingredient was confirmed by the stability study in the standard conditions used for the storage of vitamin D analogs.

Solid-phase synthesis of amino- and carboxyl-functionalized unnatural alpha-amino acid amides.

A new solid-phase synthesis efficiently incorporates three different substituents (from R(1)-X, R(2)-CO(2)H, and R(3)-NH(2)) into a glycine-based peptidomimetic scaffold. The synthetic sequence is general and is typically accomplished in >50% overall isolated yield. Alkylating agents with a range of reactivities and normal and branched primary amines give good results. Utility was demonstrated by the synthesis of a series of protected phosphotyrosine mimetics.

Distributed Drug Discovery, Part 3: using D(3) methodology to synthesize analogs of an anti-melanoma compound.

For the successful implementation of Distributed Drug Discovery (D(3)) (outlined in the accompanying Perspective), students, in the course of their educational laboratories, must be able to reproducibly make new, high quality, molecules with potential for biological activity. This article reports the successful achievement of this goal. Using previously rehearsed alkylating agents, students in a second semester organic chemistry laboratory performed a solid-phase combinatorial chemistry experiment in which they made 38 new analogs of the most potent member of a class of antimelanoma compounds. All compounds were made in duplicate, purified by silica gel chromatography, and characterized by NMR and LC/MS. As a continuing part of the Distributed Drug Discovery program, a virtual D(3) catalog based on this work was then enumerated and is made freely available to the global scientific community.

Distributed Drug Discovery, Part 2: global rehearsal of alkylating agents for the synthesis of resin-bound unnatural amino acids and virtual D(3) catalog construction.

Distributed Drug Discovery (D(3)) proposes solving large drug discovery problems by breaking them into smaller units for processing at multiple sites. A key component of the synthetic and computational stages of D(3) is the global rehearsal of prospective reagents and their subsequent use in the creation of virtual catalogs of molecules accessible by simple, inexpensive combinatorial chemistry. The first section of this article documents the feasibility of the synthetic component of Distributed Drug Discovery. Twenty-four alkylating agents were rehearsed in the United States, Poland, Russia, and Spain, for their utility in the synthesis of resin-bound unnatural amino acids 1, key intermediates in many combinatorial chemistry procedures. This global reagent rehearsal, coupled to virtual library generation, increases the likelihood that any member of that virtual library can be made. It facilitates the realistic integration of worldwide virtual D(3) catalog computational analysis with synthesis. The second part of this article describes the creation of the first virtual D(3) catalog. It reports the enumeration of 24,416 acylated unnatural amino acids 5, assembled from lists of either rehearsed or well-precedented alkylating and acylating reagents, and describes how the resulting catalog can be freely accessed, searched, and downloaded by the scientific community.

Neural network-based QSAR and insecticide discovery: spinetoram.

Improvements in the efficacy and spectrum of the spinosyns, novel fermentation derived insecticide, has long been a goal within Dow AgroSciences. As large and complex fermentation products identifying specific modifications to the spinosyns likely to result in improved activity was a difficult process, since most modifications decreased the activity. A variety of approaches were investigated to identify new synthetic directions for the spinosyn chemistry including several explorations of the quantitative structure activity relationships (QSAR) of spinosyns, which initially were unsuccessful. However, application of artificial neural networks (ANN) to the spinosyn QSAR problem identified new directions for improved activity in the chemistry, which subsequent synthesis and testing confirmed. The ANN-based analogs coupled with other information on substitution effects resulting from spinosyn structure activity relationships lead to the discovery of spinetoram (XDE-175). Launched in late 2007, spinetoram provides both improved efficacy and an expanded spectrum while maintaining the exceptional environmental and toxicological profile already established for the spinosyn chemistry.

Solid-phase synthesis of multiple classes of peptidomimetics from versatile resin-bound aldehyde intermediates.

A wide variety of highly substituted lactam containing peptidomimetic scaffolds are prepared by solid-phase synthesis from a single, versatile class of resin-bound aldehyde intermediates (1). These include monocyclics 3, bicyclics 4, tricyclics 5, and tetracyclics 6. The key intermediate 1 is readily synthesized from resin-bound natural or unnatural alpha-amino acids. The synthetic procedures permit the construction of a large diversity of substitution patterns for ready use in combinatorial chemistry. In every case, the release of final products from resin is by a cyclitive cleavage process. Since this depends on successful completion of multiple intermediate synthetic steps, the products are often quite pure, even though previous steps involve only a filtration workup. The mild conditions for many of these synthetic procedures offer the promise of using this chemistry in peptide fragment condensations to produce modified peptides, at either the N-terminus or C-terminus, or as individually assembled peptide segments with a wide variety of conformationally restricted peptidomimetic linkers at the point of juncture.

Spinosyn g: proof of structure by semisynthesis.

[reaction: see text] Spinosyn G was isolated in the late 1980s as a minor component from the broth of our potent, fermentation-derived insecticide spinosad. Its structure was then tentatively identified as 5' '-epispinosyn A (3) on the basis of (1)H and (13)C NMR data, but the 4' '-epi compound 4 could not be conclusively ruled out with the data available. Described herein are unambiguous syntheses of both 3 and 4, whereby 3 was proved identical to the natural product. Compound 4 was prepared from intact spinosyn A by a novel F-TEDA-promoted oxidative deamination to the 4' '-ketone 5, stereoselective reduction to the equatorial alcohol 6, and nitrogen incorporation via the axial azide 7. Compound 3 was obtained by coupling spinosyn A 17-pseudoaglycone (9) with the N-protected dihydropyran 16 derived from methyl l-ossaminide (14). This gave an approximately 2:1 mixture of anomeric products 17 with the desired equatorial glycoside predominating, which was then converted to 3 by N-deprotection and methylation.