Search

The halohydroxylation of 1,2-allenyl sulfides or selenides with Br(sub 2) (CuBr(sub 2) or NBS) or I(sub 2) and water demonstrate a fair good regioselectivity leading to the synthesis of synthetically important 3-organosulfur or seleno-2-haloallylic alcohols. The conclusion states that the stereoselectivity depends on the nature of X(super +) and S or Se, showing a Z-selectivity with the matched Lewis acid-base pair.

Hydration reactions of fully oxidized alumina clusters are measured with a quadrupole ion trap secondary ion mass spectrometer (IT-SIMS) 68-71, wherein the number of Lewis acid sites is determined. The observations set the stage for reactivity studies of the alumina clusters, which has the potential for close resemblance to hydroxylated surfaces.

A convergent, stereocontrolled total synthesis of the architecturally complex tregmorgenic indole alkaloid (_)-penitrem D (4) is achieved. The highlights of the synthesis include an efficient, asymmetric synthesis of the western hemisphere, the stereocontrolled assembly of the I-ring and discovery of a novel autoxidation to introduce the C(22) tertiary hydroxyl group.

alpha-Methylthreonines and alpha,beta-dimethylcysteines were synthesized through the Sharpless asymmetric dihydroxylation (AD) reaction. The novel enantioselective procedure starts with the asymmetric dihydroxylation of benzyl tiglate while exposed to (DHQ)2PHAL(AD-mix alpha) and methanesulfonamide and leads to the production of two chiral centers in one step. The procedure requires only one silica gel chromatographic purification for benzyl (2S,3S)-2-azido-3-hydroxy-2-methylbutyrate prior to hydrogenation.

The synthesis of conduramines from N-tert-butoxycarbonylpyrrole is described. Two synthetic strategies were used for the conversion of the Diels-Alder adduct of Boc-pyrrole and p-toluenesulfonylacetylene into several racemic and optically pure conduramines. One method employed the regio- and stereoselective hydroxylation of the Diels-Alder adduct to compounds, the exo-endo mixture and subsequent anionic fragmentation to the cyclohexene derivatives. Results indicate that the method can be used to prepare any imaginable conduramine derivative in racemic and pure forms.

The Mn-TMPyP/KHSO5 nuclear system can separate DNA at A-T base pair sites through hydroxylation of one C-H bond at the 5' position or both 3' side deoxyriboses next to the (A.T)3 metalloporphyrin high-affinity site. The oxidative cleavage which is succeeded by a reduction step is identical to the hydrolysis of a phosphodiester bond.

An alternative synthetic route to CBI, the fused cyclopropa(c)benz(e)indolone analogue of the CPI segment of CC-1065, involves the use of inexpensive 1, 4-naphthalenedione and benzylamine. The process uses an osmium-catalyzed dihydroxylation with N-methylmorpholine N-oxide instead of the more popular Sharpless method. The cyclopropyl ring is built through the bicyclization of a mesylated six-membered piperidine ring. Two CBI-PDE-I-dimers are synthesized and shown to possess half the antitumor potency of CC-1065 as well as its delayed lethality on mice specimens.

The synthesis of the southern pine beetle pheromone, (S)-(-)-frontalin, involves the metal-mediated construction of its carbon framework and its subsequent asymmetric dihydroxylation (AD). The coupling of the organocuprate Li2Cu(CN)(C(Ome):CH2)2 with allyl bromide provides a ketal that, after hydroboration, oxidation and Pd-catalyzed coupling with 2-bromopropene, yields the frontalin skeleton in 63% overall yield. AD of this bromide by the Sharpless method produces the optically active hormone in 35% enantiomeric excess. Osmium-based AD yields only the racemate.

Photolysis reaction of 1-methyl-9,10-anthraquinones is performed in the presence of oxygen to obtain endoperoxides that could be reduced to produce 1-hydroxymethyl-9,10-anthraquinones. The photochemical hydroxylation could also be used for total synthesis of a naturally occurring polyketide, 9'-hydroxyaloesaponarin II.

A new asymmetric synthetic method is described for (-)-swainsonine by using a chiral oxazoline precursor. The main features of this strategy are the diastereoselective oxazoline formation reaction catalyzed by palladium(0), diastereoselective dihydroxylation and the stereocontrolled allylation reaction with Ti[Cl.sub.4].

A stereocontrolled total synthesis of (-)-ephedradine A was accomplished by a Rh-catalyzed C-H insertion reaction and a sharpless asymmetric aminohydroxylation reaction. The synthesis features construction of all the secondary amines using the Ns-strategy, including macrocyclination and formation of the two amine bonds by the intramolecular ester-amine exchange reaction and the aza-Wittig reaction.

The study states that multicomponent enzyme system comprises three proteins, a hydroxylase (MMOH) which contains a pair of carboxylate-bridged diiron centers involved in O(sub 2) activation and substrate hydroxylation, a cofactorless coupling protein (MMOB), and a reductase (MMOR).(super 1,2). The result added a significant insight into the reaction of MMOH intermediate Q with substrates. The substrates fall into two well-defined categories, those for which the KIE is large and those for which it is essentially nonexistent.

The first synthesis of two naturally present acetogenins, natural solamin and reticulatacin 2, validates their absolute configuration previously identified from NMR findings. The replaced tetrahydrofuran ring, which has four stereogenic carbinol centers in a threo-trans-threo association, was decisive in this synthesis. The Sharpless asymmetric dihydroxylation reaction was used to predict the transformation of a suitably substituted (E,E)-1,5-diene, such as 3, into a threo,threo tetraol having high enantiomeric purity and forseeable absolute configuration, which would offer all four asymmetric centers in one stage.

A novel mechanism for polymer-sislica surface adhesion is presented. Alkoxysilane coupling agents reacts directly with highly strained siloxane bonds present on dehydroxylated silica. The extent of this reaction scales inversely with the surface hydroxyl concentration and increases with the dehydroxylation temperature leading to the conclusion that surface hydroxyl groups are not involved in the reaction.