Product Integration Rules at Clenshaw-Curtis and Related Points: A Robust Implementation

Product integration rules generalizing the Fej?r, Clenshaw-Curtis,and Filippi quadrature rules respectively are derived for integralswith trigonometric and hyperbolic weight factors. The Chebyshevmoments of the weight functions are found to be given by well-conditionedexpressions, in terms of hypergeometric functions ₀F₁. An a priori error estimator is discussed which is shown bothto avoid wasteful invocation of the integration rule and toincrease significantly the robustness of the automatic quadratureprocedure. Then, specializing to extended Clenshaw-Curtis (ECC) rules,three types of a posteriori error estimates are considered andthe existence of a great risk of their failure is demonstratedby large scale validation tests. An empirical error estimator,superseding them for slowly varying integrands, is found toresult in a spectacular increase in the output reliability. Finally, enhancements in the control of the interval subdivisionstrategy aiming at increasing code robustness is discussed.Comparison with the code DQAWO of QUADPACK, with about a hundredthousand solved integrals, is illustrative of the increasedrobustness and error estimate reliability of our computer codeimplementation of the ECC rules.     

Ceric ammonium nitrate on silica gel for efficient and selective removal of trityl and silyl groups

Silica gel-supported ceric ammonium nitrate (CAN-SiO2) was found effective for rapid and selective cleavage of trityl (Tr), monomethoxytrityl (MMTr), and dimethoxytrityl (DMTr) groups from protected nucleosides and nucleotides under mild conditions. Efficiency of deprotections depended upon the stability of the resultant carbocationic species: DMTr+ > MMTr+ > Tr+. Use of a catalytic amount of this solid-supported reagent can also efficiently and selectively remove the tert-butyldimethylsilyl or the triisopropylsilyl group from a primary hydroxyl functionality in di- or trisilyl ethers of ribonucleosides. A comparative study of deprotection reactions by utilization of CAN alone or CAN-SiO2 indicates a remarkable increase in the rate of the reactions involving a solid support. The mechanism of electron-transfer processes is proposed for the use of CAN-SiO2 in the removal of these protective groups from organic molecules.     

Synthesis of a Masked p -Quinone Methide β -Lactam as an active metabolite of nocardicins

Nocardicin A analogues 30, 34 , and 38 as well as the highly strained quinone methide 43 were synthesized. β -Lactam 34 was found biologically active against several Gram-negative microorganisms in vitro; pyridinium N-oxide derivative 38 possessed activity against Gram-positive S. aureus bacterium. Masked p-quinone methide β -lactam 43 exhibited significant antimicrobial activity in vitro. A mechanism involving an oxidation in vivo is proposed for the unprecedented biological properties of nocardicins.     

The Synthesis of 4-Decarboxy-4-phosphono-O-2-isooxacephems, -isopenams and -isooxacephems Containing Phosphorus at the 3-Position

Two new types of iso-oxacephems have been synthesized in which a phosphonate group replaces either the carboxyl group or C(3). The latter compound exists as a stable trialkoxyphosphonium ylide. Potassium thioacetate and O₂ in DMF are transformed in an autocatalytic, probably sulfur-catalyzed process to CH₃COOK and sulfur; the latter two reagents are sufficient to transform the methanesulfonate 7 to the isopenam 15 .     

N-Levulination of Guanosine

A procedure have been developed for the synthesis of the N-levulinoyl derivative of guanosine.     

Syntheses of Novel Isopenam and Isocephem Antibiotics. Preparation of a retinamido derivative of a highly strained β-lactam as potent anticancer agent

Syntheses of the cis-configurated isopenam 9 (Scheme 1), isocephem 14 (Scheme 2), and isocephem 19 (Scheme 3) are described. The key step in the preparation of 14 and 19 involved a Pummerer-type rearrangement of the corresponding sulfoxides 12 and 18 . These β-lactams were found to possess biological activity against several pathogenic microorganisms in vitro. The electronic activation of the lactam moiety of 19 remarkably enhanced its biological activity. A retinoic moiety was attached to 19 via an amino linker. The resultant retinamido-β-lactam 21 showed significant cytostatic activity in tracheal organ cultures obtained from vitamin-A-deficient hamsters.     

The Synthesis of 5,11,17-Trihalotetracyclo [13.3.1.13,7.19,13]henicosa-1 (19),3,5,7 (20),9,11,13 (21), 15,17-nonaene-19,20,21-triols and 5,11,17-trihalo-19,20,21-trihydroxytetracyclo [13.3.1.13,7. 19,13]henicosa-1 (19),3,5,7 (20),9,11,13(21), 15,17-nonaene-8,14-dione [1]. Cyclo-derivatives of Phloroglucide Analogues

The synthesis of the title compounds ( 1 and 3 ) is described. Some of the compounds prepared were found to be active against a number of pathogenic microorganisms in vitro. Structure-activity relationship is briefly discussed.     

Thermodynamic Complexation of Dopamine with Zinc(II) in Media with Different Dielectric Constants

The complexation of zinc(II) with dopamine has been investigated by spectrophotometric measurements in mixed solvent system at an ionic strength of 0.2 mol•dm－3 sodium chloride, employed at at (15±0.1), (25±0.1), (35±0.1) ℃ at inin a pH range of ca. 6 to ca. 7 with a high ratio of ligand to metal. The effect of solvent systems on protonation and complexation are was was discussed. Linear relationships are werewere observed by plotting lg K versus 1/D, where K and D show stability and dielectric constants, respectively.     

Synthesis of ethyl cis 2-[(Diethoxyphosphoryl)methyl]-7-oxo-3-phenyl-6-phthalimido-l-azabicyclo[3.2.0]hept-3-ene-2-carboxylate and Methyl cis-2-Bromo-3-methyl-8-oxo-7-phthalimido-4-oxa-1-azabicyclo[4.2.0]octane-2-carboxylate

The synthesis of a Δ¹-carbapenem and two β-lactams possessing a Br-atom at the N-substituting center not involved in the lactam ring and bearing the carboxyl group is described. The β-lactams having this kind of Br-substitution are more susceptible to nucleophilic attack than those having a conjugated double bond with the N-atom of the β-lactam ring. DBU is found to be an excellent reagent for the elimination of the silyloxy function. Moreover, a simple method for the addition of diethyl phosphite to an α, β-unsaturated double bond using a catalytic amount of NaH is described.     

Catalytic effect of tetrabutylammonium fluoride in the preparation of secoribo-nucleosides

A general and rapid procedure is developed for the preparation of secoribo-nucleoside analogues. Bu₄NF has a marked effect on the condensation of guanine ( 5 ) with 2-(chloromethoxy)ethyl benzoate ( 2 ) or 1-halo-2-(chloromethoxy)ethanes 12 and 16 . Condensation and deprotection of the acyl protecting group and nucleophilic displacement of the halogen atoms to yield 9-[(2-hydroxyethoxy)methyl] guanine ( 9 ) occurred in one step.