A study of the hydrolysis of formamide is reported with the aims of isolating the water reaction for hydrolysis from the acid and base hydrolysis terms and determining the solvent deuterium kinetic isotope effect (dkie) on base-catalyzed hydrolysis. Respective activation parameters (ΔH‡ and ΔS‡) of (17.0 ± 0.4) kcal mol–1 and (–18.8 ± 1.3) cal mol–1 K–1 for the acid reaction and (17.9 ± 0.2) kcal mol–1 and (–11.1 ± 0.5) cal mol–1 K–1 for the base reaction were determined from Eyring plots of the second-order rate constants over the range of 27–120°C. Kinetic studies at the minima of the pH/rate profiles in the pH range from 5.6 to 6.2 in MES buffers at 56°C, and in the pH range of 4.25–6.87 in acetate and phosphate buffers at 120°C are reported. At 56°C the available data fit the expression k56obs = 0.00303[H3O+] + 0.032[HO–] + (3.6 ± 0.1) × 10–9, while at 120°C the data fit k120obs = (0.15 ± 0.02)[H3O+] + (3.20 ± 0.24)[HO–] + (1.09 ± 0.29) × 10–6. Preliminary experimental estimates of Ea (ln A) of 22.5 kcal mol–1 (15.03) for the water rate constant (kw) are calculated from an Arrhenius plot of the 56 and 120°C data giving an estimated kw of 1.1 × 10–10 s–1 (t1/2 = 199 years) at 25°C. Solvent dkie values of kOH/kOD = 1.15 and 0.77 ± 0.06 were determined at [OL–] = 0.075 and 1.47 M, respectively. The inverse value is determined under conditions where the the first step of the reaction dominates and is analyzed in terms of a rate-limiting attack of OL–.Key words: formamide, activation parameters, water reaction, acid and base hydrolysis, solvent kinetic isotope effect.

Highly fluorescent π-conjugated polycyclic azaborines can be prepared from B,N-heterocyclic compounds with a BR2 -CH2 unit through the elimination of an R-H molecule (see scheme). These clean photoelimination reactions occur both in solution and in polymers doped with the precursors.

Abstract:The structures and stereochemistry of 14 taxanes isolated from Taxus cunadensis have been rigorously established by high-resolution NMR techniques and mass spectrometry. Taus canadensis is the only yew that accumulates 9-dihydro-13-acetylbaccatin 111 (also called 7,9-deacetylbaccatin VI) as the most abundant taxane. Five 9-dihydrotaxanes derived from the Canadian yew are novel natural products not reported in the needles of other species of yew (8-11, 14, Fig. 1).

Three antibiotic peptides, LP237-F8 (I), F5 (2), and F7 (3), were isolated from the liquid culture of the fungus Toly~>ocladi~imgeorlrs. Chemical shift assignments of the 'H and "C NMR resonances and sequencing of these metabolites were achieved by extensive high-field 2D NMR spectroscopy. The N-terminal of peptides 1 and 2 is protected with an octanoyl (Oc) fatty acid unit, whereas that of peptide 3 is protected with a decanoyl (Dec) unit. The C-terminal of all three peptides is protected with the amino alcohol leucinol (Lol). All three metabolites contain the common amino acids Ala, Phe or Tyr, Pro, and Gln, as well as the unusual amino acid a-aminoisobutyric acid (Aib). In addition, peptides 1 and 2 contain the amino acid a-amino-aethyl-12-pentanoic acid (a-ethylnorvaline, EtNor), which has not been previously reported as a constituent of a natural product. Metabolites 1 , 2 , and 3 are new members of the class of natural products known as peptaibols.Key rvords: Tolypoclrirlilirn geodes, peptaibols, leucinol, a-amino-a-ethyl-11-pentanoic acid.RCsumC : On a isole trois peptides antibiotiques, LP237-F8 (I), F5 (2) et F7 (3) h partir de milieux de culture liquides du champignon Tol.yl,oclndirirrl geodes. On a attribuC les deplacements chimiques des spectres RMN du 'H et du "C ainsi que la sequence de ces mitabolites en faisant un usage extensif de la spectroscopie RMN 2D ii haut champ. Le groupe N-terminal des peptides 1 et 2 est protege par une unite d'acide gras octanoyle (Oc) alors que celui du peptide 3 est protege par une unit6 dCcanoyle (Dec.) Le groupe C-terminal de chacun de ces trois peptides est protCgC par l'alcool amin6 leucinol (Lol). Les trois metabolites contiennent les acides arnines usuels Ala, PhC ou Tyr, Pro et Gin ainsi que I'acide a-aminoisobutyrique (Aib), un acide aniinC inhabituel. De plus, les peptides 1 et 2 contiennent l'acide aminC, a-amino-a-Cthyl-n-pentano'ique (a-Cthylnorvaline, EtNor), dont on n'a jamais rapport6 la presence comme constituant d'un produit naturel. Les mCtabolites 1 , 2 et 3 sont de nouveaux membres de la classe des produits naturels connus comme des peptaibols.Most clGs : Tolypocladi~irrl geodes, peptai'bols, leucinol, acide a-amino-a-ethyl-12-pentano'ique.[Traduit par la redaction]

Identification of a macrocyclic tambjamine natural product, tambjamine MYP1, from a marine bacterium that may enhance bioactivity by restraining bond rotation.

A PPh2- and BMes2-functionalized (Mes = mesityl) 1,8-naphthalene molecule (1) has been synthesized and fully characterized. Compound 1 is a highly congested molecule with a P–B dative bond. NMR studies support that the P–B bond in 1 is persistent in solution. Compound 1 is thermally and photochemically stable. It is highly fluxional in solution. The only reactivity it displays is its reactions with halogen molecules (PhI·Cl2 and I2), leading to the isolation of a hydrolyzed product 2, in which an oxygen atom is inserted between the P and B atom. The crystal structures of 1 and 2 have been determined by single-crystal X-ray diffraction analyses. A DFT computational study established that the open form of 1 has a P–B separation distance of 3.00 Å, much longer than the closed one (2.23 Å). Furthermore, a computational study showed that the energy difference between the two forms is very small, ∼1 kcal/mol, which can be attributed to the highly congested nature of the molecule.

Caught in the act: An alkyl alkene Zr(IV) complex (see picture; Cp = C(5)H(5)) has been synthesized and characterized for the first time. The alkene bonding mode is highly asymmetric, and C2 is quite carbocationic. There is also evidence for rotation about the C1-C2 bond. This extremely unusual complex provides an exemplar of previously unknown intermediates in Ziegler-Natta and carbocationic polymerization reactions of alkenes.

Amino-borane functionalization is the key for isolating rare air-stable dihydrophenanthrene intermediates in stilbene photocyclization.