Rapid entry into the cryptophycin core via an acyl-beta-lactam macrolactonization: total synthesis of cryptophycin-24.

[see structure]. An efficient, concise approach to the macrolide core of the cryptophycins, potent antimitotic agents, has been achieved. The reaction sequence features a novel macrolactonization utilizing a reactive acyl-beta-lactam intermediate that incorporates the beta-amino acid moiety within the 16-membered macrolide core. This highly modular approach, which allows for multiple alterations throughout the structure, was successfully applied to the total synthesis of cryptophycin-24.

Chest wall irradiation with MLC-shaped photon and electron fields.

PURPOSE: To improve the treatment technique for chest wall irradiation, using the multileaf collimator (MLC) of the MM50 Racetrack Microtron to shape both photon and electron beams, and to check the dose delivery in the match-line region of these fields for the routine and improved technique. METHODS AND MATERIALS: Using diode and film phantom measurements, the optimal number of photon beam segments and their positions relative to the electron beam were determined. On phantoms, and during actual patient treatment using in vivo dosimetry, the dose homogeneity in the match-line region was determined for both the routine and improved techniques. RESULTS: Three photon beam segments (9-mm gap, perfect match, and 9-mm overlap) were used to match the electron beam, resulting in minimum-maximum dose values in the match-line region of 88-109%, compared to 80-115% for the routine technique (2 photon beam segments). During patient treatment, the average minimum and maximum dose values were 95% and 115%, respectively, compared to 78% and 127%, respectively, for the routine technique. The interfraction variation in dose delivery was reduced from 11.0% (1 SD) to 4.6% (1 SD). The actual treatment time was reduced from 10 to 4.5 min. CONCLUSION: Using the MLC of the MM50 to shape both photon and electron beams, an improved treatment technique for chest wall irradiation was developed, which is less labor intensive, faster, and yields a more homogeneous, and better reproducible dose delivery.

Total synthesis of cryptophycin-24 (Arenastatin A) amenable to structural modifications in the C16 side chain.

Two efficient protocols for the synthesis of tert-butyl (5S,6R,2E, 7E)-5-[(tert-butyldimethylsilyl)oxy]-6-methyl-8-phenyl-2, 7-octadienoate, a major component of the cryptophycins, are reported. The first utilized the Noyori reduction and Frater alkylation of methyl 5-benzyloxy-3-oxopentanoate to set two stereogenic centers, which became the C16 hydroxyl and C1' methyl of the cryptophycins. The second approach started from 3-p-methoxybenzyloxypropanal and a crotyl borane reagent derived from (-)-alpha-pinene to set both stereocenters in a single step and provided the dephenyl analogue, tert-butyl (5S,6R,2E)-5-[(tert-butyldimethylsilyl)oxy]-6-methyl-2, 7-octadienoate, in five steps. This compound was readily converted to the 8-phenyl compound via Heck coupling. The silanyloxy esters were efficiently deprotected and coupled to the C2-C10 amino acid fragment to provide desepoxyarenastatin A and its dephenyl analogue. The terminal olefin of the latter was further elaborated via Heck coupling. Epoxidation provided cryptophycin-24 (arenastatin A).

Enantioselective synthesis of a 3'-dephenylcryptophycin synthon.

An enantioselective synthesis of tert-butyl (5S,6R)-(E)-5-tert-butyldimethylsilyloxy-6-methyl-2,7-octadieno ate, a precursor for the synthesis of the antimitotic macrolides cryptophycin A and arenastatin A (cryptophycin-24), is presented. The key step in the reaction sequence features a crotyl boration that sets both stereocenters that become the C16 hydroxyl and Cl' methyl in the cryptophycins. Homologation of the terminal olefin via a Heck reaction is presented.

Peripheral venous monitoring with acute blood volume alteration: cuff-occluded rate of rise of peripheral venous pressure.

We investigated the use of a new peripheral hemodynamic monitoring technique, the cuff-occluded rate of rise of peripheral venous pressure (CORRP), in the assessment of volume status in fluid overload. Seven adult mongrel dogs were given a general anesthetic, and monitoring lines were inserted. The animals were then subjected to an incremental volume overload of approximately 13% of estimated initial blood volume at 5-min intervals until a total volume infusion nearly equal to the animal's initial blood volume was reached. Comparison of the various monitoring techniques (e.g., cardiac output, CVP, systemic BP, pulmonary wedge pressure) demonstrated that the peripheral measurement of CORRP had better correlation with known administered volume (r = .96) than any of the other variables. The sensitivity of each of the variables in assessing small amounts of volume overload was also studied. The volume of crystalloid infusion necessary to cause a clinically significant change (defined as greater than 2 SD above the baseline mean) was compared for each of the monitoring variables. CORRP was equivalent to the other variables in sensing early volume overload. In summary, in the anesthetized animal model CORRP appears to be a sensitive, minimally invasive method of assessing volume status in acute volume overload. The efficacy of CORRP in a canine hemorrhagic shock and reperfusion model had previously been demonstrated. This technique could be clinically applicable in situations such as trauma with hemorrhagic shock, intraoperative volume changes, and in the assessment of intravascular volume after resuscitation.

The purification and characterization of human kidney L-arginine:glycine amidinotransferase.

Human kidney L-arginine:glycine amidinotransferase (transamidinase) has been purified to a homogeneous state as defined by native and sodium dodecyl sulfate gel electrophoresis and by ultracentrifugation (sedimentation equilibrium) experiments. The four steps in the isolation procedure were chromatography with DEAE-cellulose, gel filtration with Sephadex G-150, chromatography with phenyl Sepharose, and high-pressure liquid chromatography with hydroxylapatite. The final product represented a 90-fold purification of the enzyme. Human kidney transamidinase is a dimer with a molecular mass of 89,000 Da and subunit masses of 44,000 Da. The Km for arginine and glycine were both 2.5 mM and the Vmax was 0.5 mumol ornithine/min/mg protein. The ultraviolet absorption spectrum, specific activity, and isoelectric points were determined for human kidney transamidinase. Multiple forms of the enzyme were obtained by isoelectric focusing. Human kidney transamidinase cross-reacted with polyclonal antibodies raised to rat kidney transamidinase. All of the properties of human kidney transamidinase that we have examined were similar to those of rat kidney transamidinase. A close evolutionary relationship between the rat and human kidney transamidinase is suggested.