Direct-injection NMR (DI-NMR): a flow NMR technique for the analysis of combinatorial chemistry libraries.

A new tool for analyzing compound libraries by NMR has been developed. Aliquots of solution-state samples (between 120 and 350 microL) are directly injected, using a standard liquids handler, into an NMR (LC-NMR) flow probe. Automated NMR software tracks--and suppresses--intense signals arising from the nondeuterated solvents used (if any) and acquires high-sensitivity one-dimensional 1H NMR spectra. An 88-member combinatorial library, dissolved in DMSO and stored in a 96-well microtiter plate, has been analyzed a number of ways using this technique. This nondestructive technique, which we call direct-injection NMR (DI-NMR) and which is embodied in our versatile automated sample changer (VAST) hardware, has proven to be both routine and robust. Our success in automatically acquiring the NMR data for entire plates of library compounds (within 4-8 h) has caused us to develop new ways to display and analyze the resulting NMR data, as will be shown here.

The role of dianion coupling in the synthesis of dibenzylbutane lignans.

Dianion coupling reactions have been used to prepare structurally related lignan natural products in racemic form. A readily available alpha-idocarboxylic acid 10 has been employed in separate sequences to afford the tetrahydrofuran lignan burseran [6] and the butyrolactone lignan deoxypodorhizon [7]. The key strategy for both burseran and deoxypodorhizon involved reaction of the appropriate dianion with an alpha-iodo carboxylate salt 13. Equilibration under acid or base was employed to create the trans stereochemistry of the substituted benzyl side chains of both burseran and deoxypodorhizon. To achieve proper dianion reactivity and to avoid side reactions in the synthetic sequence to deoxypodorhizon, it was necessary to develop the chemistry of acylsulfonamide dianions. As a further structure proof, our synthetic deoxypodorhizon was also utilized as a substrate in a successful sequence to isostegane [8], a known relay intermediate to the antineoplastic prototype steganacin [9].

Stereoselectivity questions in the synthesis of wikstromol.

While the Davis oxaziridine reagent generally affords oxidation products based on simple steric considerations, this concept appears to have some limitations when used to design natural product synthetic strategies. Thus, an example has been found in which the observed stereoselectivity of an enolate oxidation is "anomalous." The system in question involves an enolate oxidation performed on a lignan butyrolactone having highly oxygenated aromatic rings. Besides establishing the course of this oxidation and confirming the proposed structure of wikstromol and related lignans, a single-crystal X-ray study on a wikstromol stereoisomer provides complementary data for comparison with the "natural" isomer.

Spiro hydantoin aldose reductase inhibitors.

Sorbitol formation from glucose, catalyzed by the enzyme aldose reductase, is believed to play a role in the development of certain chronic complications of diabetes mellitus. Spiro hydantoins derived from five- and six-membered ketones fused to an aromatic ring or ring system inhibit aldose reductase isolated from calf lens. In vivo these compounds are potent inhibitors of sorbitol formation in sciatic nerves of streptozotocinized rats. Optimum in vivo activity is reached in spiro hydantoins derived from 6-halogenated 2,3-dihydro-4H-1-benzopyran-4-ones (4-chromanones). In 2,4-dihydro-6-fluorospiro[4H-1-benzopyran-4,4'-imidazolidine]-2',5 '-dione, the activity resides exclusively in the 4S isomer, compound 115 (CP-45,634, USAN: sorbinil). This compound is currently being used to test, in humans, the value of aldose reductase inhibitors in the therapy of diabetic complications.