greater than the response of similarly treated blanks at the 5-gg level and 400 times greater than the response of methanol to flame ionization detection (1 ,5 ) . The compound in which the methanol is to be determined, must be somewhat water soluble. Complete dissolution of the sample weight taken in the 1-ml water-urea mixture used is necessary to free the methanol for subsequent reaction. Ac...

The conserved pterin dithiolene ligand that coordinates molybdenum (Mo) in the cofactor (Moco) of mononuclear Mo enzymes can exist in both a tricyclic pyranopterin dithiolene form and as a bicyclic pterin-dithiolene form as observed in protein crystal structures of several bacterial molybdoenzymes. Interconversion between the tricyclic and bicyclic forms via pyran scission and cyclization has b...

A palladium-mediated intramolecular aryl–aryl coupling reaction was applied to the total synthesis of bioactive natural products, graphislactone G (1), and palmariols (2) B (3), which possess an unusual chloro-subsutituent on 6H-dibenzo[b,d]pyran-6-one skeleton. Based transition state model reaction, mechanistic aspect for regioselectivity is also discussed.

In the title compound, C26H24O5, the pyran ring has a flattened-boat con-formation, with the 1,4-related ether O and methine C atoms lying 0.1205 (18) and 0.271 (2) Å, respectively, above the least-squares plane involving the doubly bonded C atoms (r.m.s deviation = 0.0208 Å). An envelope conformation is found for the cyclo-hexene ring, with the flap atom being the middle methyl-ene C atom, lyi...

5-Fluorouracil (5-FUra), 5-deoxy-5-fluorouridine (5'dFUrd), and 5-fluorouridine were compared for their relative antitumor activity, their capacity to inhibit leukocyte exudation and macrophage (macrophage) killing of tumor cells in vivo and in vitro, and their ability to induce leukopenia and monocytopenia. 5'dFUrd was less toxic than 5-FUra and exhibited anti-Ehrlich ascites activity over a w...

In the title compound, C(6)H(6)O(4), inter- and intra-molecular hydrogen bonds are observed which help to establish the crystal structure. There are weak π-π interactions between pyran rings separated by 3.5692 (9) Å.

[reaction: see text] A diastereoselective tandem Stille-oxa-electrocyclization reaction provides access to the core of the diterpenoid natural product saudin. Additionally, this new reaction sequence was extended to the convergent preparation of related polycyclic pyran systems.

The title compound, C11H10O3, is a phenyl-subsituted dihydro-pyran-dione in which the heterocycle adopts a boat conformation with the phenyl substituent canted 72.14 (5)° relative to the mean plane of the heterocycle.

The pyran ring of the title compound, C(13)H(18)N(2)O(3), is almost planar (r.m.s. deviation = 0.059 Å). The crystal packing is stabilized by N-H⋯O and N-H⋯N hydrogen bonds.

A highly efficient synthesis of diversely substituted 2H-pyran-2-ones and indenes through Brønsted acid promoted tandem reaction of the readily obtainable 3-hydroxyhexa-4,5-allenic esters under extremely mild conditions has been developed.