Tert-butyl Thiol Research Articles

HPLC with Electrochemical and Fluorescence Detection of the OPA/2-Methyl-2-propanethiol Derivative of Fumonisin B1

Abstract The o-phthalaldehyde (OPA) derivative of fumonisin B1 was prepared in the presence of 2-methyl-2-propanethiol (tert-butyl thiol). A hydrodynamic voltammogram for the derivative indicated that the optimum voltage for maximum electrochemical response was ±0.7 V. The electrochemical response of the OPA/tert-butyl derivative was unstable. However, the fluorescence response was found to be stable for over an hour after an initial 30 minute reaction time. The minimum detectable limit (MDL) of the OPA/tert-butyl derivative using fluorescence detection was 30 ng/ml as compared to 250 ng/ml for electrochemical detection.

Selective Generation of Free Radicals from Epoxides Using a Transition-Metal Radical. A Powerful New Tool for Organic Synthesis

Bis(cycIopentadienyl)titanium(III) chloride reacts with epoxides by initial C-0 homolysis. The regiochemistry of the opening is determined by the relative stabilities of the radicals. Depending on the reaction partners, these radicals undergo intramolecular (hex-5-enyl cyclization) or intermolecular additions to olefins. The resultant radicals are efficiently scavenged by a second equivalent of Ti(II1) to afford the corresponding Ti(1V) derivative. Treatment of this intermediate with electrophiles such as H+ or halogens provides a route to functionalized cyclopentanes and other useful products. The radical initially formed from an epoxide can also be trapped by H-atom donors such as 1,4- cyclohexadiene or tert-butyl thiol, resulting in an overall reduction of the epoxide. In the absence of a H-atom donor or an olefin, this radical is trapped by Ti(, resulting in a fl-oxido-Ti organometallic species which undergoes facile elimination to give an olefin. The reaction conditions are remarkably mild and are applicable to very sensitive substrates. The considerable utility of epoxides as building blocks for organic synthesis reflects both their ready availability and their ability to undergo selective nucleophilic substitution reactions (eq la) with predictable stereochemistry.' In contrast, the two-

Rate constants and Arrhenius functions for hydrogen atom transfer from tert-butyl thiol to primary alkyl radicals

Rate constants and Arrhenius functions for hydrogen atom transfer from tert-butyl thiol to primary alkyl radicals

1-(tert-butylthio)-1,2-hydrazinedicarboxylic acid derivatives. New reagents for the introduction of the S-tert-butylthio group into cysteine and cysteine derivatives.

The sterically hindered tert-butyl thiol reacts smoothly with azodicarboxylic acid derivatives only upon addition of catalytic amounts of sodium alcoholate, yielding crystalline and analytically well characterized 1-(tert-butylthio)-1,2-hydrazinedicarboxylic acid derivatives. These sulfur-activated reagents were found to be stable on storage and well suited as tert-butylthio carriers for the introduction of this thiol-protecting group on cysteine, cysteine derivatives and cysteine peptides; the related compounds are obtained in high yields.

CATALYTIC HYDROGENOLYSIS IN LIQUID AMMONIA.* CLEAVAGE OF Nα‐BENZYLOXYCARBONYL GROUPS FROM CYSTEINE‐CONTAINING PEPTIDES WITH tert‐BUTYL SIDE CHAIN PROTECTION

To exemplify the extension to synthesis of sulfur-containing peptides of the Nalpha-benzyloxycarbonyl and side chain tert-butyl protective group combination, somatostatin has been synthesized via incremental chain elongation starting from the COOH-terminal cysteine. Cleavage of the Nalpha-benzyloxycarbonyl groups was achieved in high yield, at each stage, by palladium-catalyzed hydrogenation in liquid ammonia. All side chain functionalities including the cysteine thiol groups were blocked by tert-butyl-derived groups. Each gave rise to individual n.m.r. signals which permitted sensitive characterization of all intermediate protected peptides. Mild conditions were used for the removal of all protecting groups from the completed somatostatin tetradecapeptide. The tert-butyl thiol protective groups were readily and completely cleaved by mercuric acetate at pH 4. Oxidation of dihydrosomatostatin with potassium ferricyanide provided somatostatin in good yield. The results indicate that the absolute selectivity between alpha-amine and side chain protective group cleavage afforded by Nalpha-benzyloxycarbonyl hydrogenolysis in the presence of omega-tert-butyl groups may now be extended to synthesis of cysteine- and methionine-containing peptides.