Convergent assembly of highly potent analogues of bryostatin 1 via pyran annulation: bryostatin look-alikes that mimic phorbol ester function

Highly potent bryostatin analogues which contain the complete bryostatin core structure have been synthesized using a pyran annulation approach as a key strategic element. The A ring pyran was assembled using a pyran annulation reaction between a C1-C8 hydroxy allylsilane and an aldehyde comprising C9-C13. This pyran was transformed to a new hydroxy allylsilane and then coupled with a preformed C ring aldehyde subunit in a second pyran annulation, with concomitant formation of the B ring. This tricyclic intermediate was elaborated to bryostatin analogues which displayed nanomolar to subnanomolar affinity for PKC, but displayed properties indistinguishable from a phorbol ester in a proliferation/attachment assay.     

First-principles thermochemistry for the production of TiO2 from TiCl4

Despite the industrial importance of the process, the detailed chemistry of the high-temperature oxidation of titanium tetrachloride (TiCl4) to produce titania (TiO2) nanoparticles remains unknown, partly due to a lack of thermochemical data. This work presents the thermochemistry of many of the intermediates in the early stages of the mechanism, computed using quantum chemistry. The enthalpies of formation and thermochemical data for TiOCl, TiOCl2, TiOCl3, TiO2Cl2, TiO2Cl3, Ti2O2Cl3, Ti2O2Cl4, Ti2O3Cl2, Ti2O3Cl3, Ti3O4Cl4, and Ti5O6Cl8 were calculated using density functional theory (DFT). The use of isodesmic and isogyric reactions was shown to be important for determining standard enthlapy of formation (Delta(f)H(degree)(298K)) values for these transition metal oxychloride species. TiOCl2, of particular importance in this mechanism, was also studied with CCSD(T) and found to have Delta(f)H(degree)(298K) = -598 +/- 20 kJ/mol. Finally, equilibrium calculations were performed to identify which intermediates are likely to be most prevalent in the high temperature industrial process, and as a first attempt to identify the size of the critical nucleus.     

Advantages of synthesizing trans-1,2-cyclohexanediol in a continuous flow microreactor over a standard glass apparatus

Comparison is made between the preparation of trans-1,2-cyclohexanediol in standard glassware (conventional batch production) and in a microreactor (continuous flow production). The reaction sequence involved two exothermic steps where the standard procedure demands slow reagent addition and careful temperature control. In the microreactor, the reaction could be carried out safely with up to 3 times higher reagent concentration. Synthetic benefits were a faster reaction rate and a higher purity product free of colored impurities (a feature of the batch procedure).     

On a Model for Fires in Tunnel Network Structures

A one dimensional model to describe the dynamics of tunnelfires is used to model tunnel network structures. The corresponding conditions at the nodes are formulated. A numerical methods is presented. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Identification of m-Mentha-3(8),6-diene (Isosylveterpinolene) in Black Pepper Oil

m-Mentha-3(8),6-diene (&sequals n01; isosylveterpinolene; 5 ), which has not been found in nature before, was shown by GC/MS analysis and co-injection with a synthetic sample to be present to the extent of 0.12 – 0.17% in black and green pepper oil. The synthetic reference 5 was prepared by deconjugation of 3-methylcyclohex-2-en-1-one ( 1 ), subsequent alkylation with lithium 2-lithio-2-methylpropanoate, and decarboxylative dehydration of the resulting hydroxycarboxylic acid 3 employing dimethylformamide dimethyl acetal. On polar GC columns, 5 was eluted between p-cymene and terpinolene, and was characterized by an MS similar to that of terpinolene, but with the fragment m/z 121 (59, [M−Me]⁺) being less intense than that of the molecular ion at m/z 136 (67, M⁺). Since m-mentha-3(8),6-diene was also found to the extent of 0.24% in the headspace of ground black peppercorns, it can be considered to be of genuine natural origin, and thus is the first established example of a naturally occurring m-menthadiene.     

Synthesis of Tricyclic Ketones with Sesquiterpene Skeletons by Acid-Catalyzed Rearrangement of β-Monocyclofarnesol

Starting from dihydro-β-ionone ( 6 ) a mixture of three tricyclic ketones with sesquiterpene skeletons 14 , 15 , and 16 was prepared by Wittig-Horner reaction with triethyl phosphonoacetate, Red-Al^® reduction, acid-catalyzed rearrangement of the resulting β-monocyclofarnesol ( 7 ), alkaline hydrolysis of the formates 8 – 10 , and subsequent molybdenium-catalyzed oxidation. The mechanistic background of the acid-catalyzed rearrangement of β-monocyclofarnesol ( 7 ) is discussed in detail. The resulting tricyclic ketones 14 – 16 exhibit intense woody odor notes with peppery vetiver or camphoraceous cedarwood aspects.