Chi-Sing Lee

A novel chiral terpyridine macrocycle as a fluorescent sensor for enantioselective recognition of amino acid derivativesElectronic supplementary information (ESI) available: plots for estimation of binding constants for tpy macrocycle 1 with (R)-PhEtOMe. See http://www.rsc.org/suppdata/cc/b3/b313960c/

Terpyridine macrocycle 1 is shown to be a strong chelating agent for organic ammonium salts and also a useful chromophore in fluorescent sensing. It exhibits very good enantioselectivity (K(obs)(S)/K(obs)(R)= 3.8) in chiral discrimination of alpha-phenylglycine methyl ester hydrochloride (PhEtOMe).

Synthesis of the central C18–C30 core of the phorboxazole natural products

Abstract A direct synthesis of the central C18C30 core of the phorboxazole natural products has been developed. This involves construction of an acyclic acrylate using Patersons ( E )-enol borinate aldol methodology followed by an intramolecular hetero-Michael addition to form the central pyran ring of the natural products.

Base-catalyzed Diels-Alder reactions of 2H-pyran-2,5-diones: a mild approach to basiliolide B.

A new class of base-catalyzed Diels-Alder reactions of 2H-pyran-2,5-diones has been developed using catalytic amount of dicyclohexylmethylamine in tert-butyl alcohol. This method has been successfully employed for construction of the tricyclic core of basiliolide B at room temperature with good yields and exclusive endo selectivity.

Construction of the Tricyclic Furanochroman Skeleton of Phomactin A via the Prins/Conia-Ene Cascade Cyclization Approach

A substrate-controlled asymmetric Prins/Conia-ene cascade cyclization has been developed with In(OTf)(3) in CH(3)CN from 0 to 70 °C. These conditions afforded very good yields of the 1-oxadecalin product in one pot and effectively suppressed the racemization of the 1-oxadecalin product with almost no enantiomeric excess (ee) loss. This cascade cyclization has been successfully employed for the construction of the highly functionalized 1-oxadecalin unit of phomactin A with an acyclic β-keto ester and an alkynal as the substrates via a one-pot operation (66% yield, single diastereomer). The 1-oxadecalin moiety has been readily converted to the tricyclic furanochroman skeleton of phomactin A via the epoxidation/dealkoxycarbonylation protocol under very mild conditions with 52% yield in three steps.

Total Synthesis of Phorboxazole A via de Novo Oxazole Formation: Strategy and Component Assembly

The phorboxazole natural products are among the most potent inhibitors of cancer cell division, but they are essentially unavailable from natural sources at present. Laboratory syntheses based upon tri-component fragment coupling strategies have been developed that provide phorboxazole A and analogues in a reliable manner and with unprecedented efficiency. This has been orchestrated to occur via the sequential or simultaneous formation of both of the natural products oxazole moieties from two serine-derived amides, involving oxidation-cyclodehydrations. The optimized preparation of three pre-assembled components, representing carbons 3-17, 18-30, and 31-46, has been developed. This article details the design and syntheses of these three essential building blocks. The convergent coupling approach is designed to facilitate the incorporation of structural changes within each component to generate unnatural analogues, targeting those with enhanced therapeutic potential and efficacy.

Amine-induced Michael/Conia-ene cascade reaction: application to a formal synthesis of (+/-)-Clavukerin A.

An efficient and versatile amine-induced Michael/Conia-ene cascade cyclization reaction has been developed for establishing 6,6- and 5,7-bicyclic fused carbocycles with simple acyclic beta-ketoesters as the substrates in one-pot condition and this new cyclization method has been successfully utilized in a formal synthesis of (+/-)-Clavukerin A.

Formal syntheses of (±)-platensimycin and (±)-platencin via a dual-mode Lewis acid induced cascade cyclization approach.

A mild and efficient dual-mode Lewis acid induced Diels-Alder (DA)/carbocyclization cascade cyclization reaction has been developed for construction of the tricyclic core of ent-kaurenoids in one pot with the aid of a theoretical study on the π,σ-Lewis acidities of a variety of Lewis acids. With ZnBr2 as the dual-mode Lewis acid, a series of substituted enones and dienes underwent DA/carbocyclization cascade cyclization reaction smoothly at room temperature and provided the tricyclic cyclized products in one pot with good yields and high diastereoselectivity. The tricyclic cyclized product has been successfully utilized as a common intermediate for formal syntheses of (±)-platensimycin and (±)-platencin.

Total synthesis of phorboxazole A via de novo oxazole formation: convergent total synthesis.

The phorboxazoles are mixed non-ribosomal peptide synthase/polyketide synthase biosynthetic products that embody polyketide domains joined via two serine-derived oxazole moieties. Total syntheses of phorboxazole A and analogues have been developed that rely upon the convergent coupling of three fragments via biomimetically inspired de novo oxazole formation. First, the macrolide-containing domain of phorboxazole A was assembled from C3-C17 and C18-C30 building blocks via formation of the C16-C18 oxazole, followed by macrolide ring closure involving an intramolecular Still-Genarri olefination at C2-C3. Alternatively, a ring-closing metathesis process was optimized to deliver the natural products (2Z)-acrylate with remarkable geometrical selectivity. The C31-C46 side-chain domain was then appended to the macrolide by a second serine amide-derived oxazole assembly. Minimal deprotection then afforded phorboxazole A. This generally effective strategy was then dramatically abbreviated by employing a total synthesis approach wherein both of the natural products oxazole moieties were installed simultaneously. A key bis-amide precursor to the bis-oxazole was formed in a chemoselective one-pot, bis-amidation sequence without the use of amino or carboxyl protecting groups. Thereafter, both oxazoles were formed from the key C18 and C31 bis-N-(1-hydroxyalkan-2-yl)amide in a simultaneous fashion, involving oxidation-cyclodehydrations. This synthetic strategy provides a total synthesis of phorboxazole A in 18% yield over nine steps from C3-C17 and C18-C30 synthetic fragments. It illustrates the utility of a synthetic design to form a mixed non-ribosomal peptide synthase/polyketide synthase biosynthetic product based upon biomimetic oxazole formation initiated by amide bond formation to join synthetic building blocks.

Total synthesis of (-)-teucvidin.

A concise enantioselective synthesis of (-)-teucvidin has been achieved. Our synthetic strategy involved the diastereoselective Michael/Conia-ene cascade cyclization reaction for rapid establishment of the cis-decalin skeleton with three new stereogenic centers in one pot (72%, single diastereomer), the epoxidation/dealkoxycarbonylation protocol for construction of the fused furanone moiety, and the O-allylation/Claisen rearrangement protocol for construction of the all-carbon quaternary center at C9 of the clerodane skeleton.

A highly convergent cascade cyclization to cis-hydrindanes with all-carbon quaternary centers and its application in the synthesis of the aglycon of dendronobiloside A.

An efficient and versatile ZnBr(2)-catalyzed Diels-Alder/carbocyclization cascade reaction has been developed for construction of highly functionalized cis-hydrindanes (70-96% yields with high diastereoselectivity), and it has been successfully utilized in the synthesis of the aglycon of dendronobiloside A.