The total synthesis of the title compounds has been accomplished. The key step involves the kinetic stereoselective conversion of 19 → 20. The synthesis of 20 represents for the first time a direct method for constructing exo-pyrroloindoles from protected tryptophans in a highly diastereoselective manner. This step was followed by reverse prenylation (see conversion of 20 → 27). Using the methodology worked out for the titled compounds, a practical synthesis of several promising MDR reversal agents was possible. Biological data that provided the basis for selection of candidates for advanced study are presented. Preliminary profiling of the zones of the molecules that are responsive to changes while still retaining MDR reversal ability are described. On the basis of these findings, compounds 2, 50, and 51 were selected for more extensive biological follow-up.

RNA interference in mammalian cells is actively used to conduct genetic screens, to identify and to validate targets, and to elucidate regulators and modifiers of cellular pathways. To ensure the specificity and efficacy of the active 21mer siRNA molecules, it is pertinent to develop a strategy for their rational design. Here we show that most functional siRNAs have characteristic sequence features. We tested 601 siRNAs targeting one exogenous and three endogenous genes. The efficacy of the siRNAs was determined at the protein level. Using a decision tree algorithm in combination with information analysis, our analyses revealed four sets of rules with a mean knockdown efficacy ranging from 60% to 73%. (To distinguish between percentages used to describe the quality of an siRNA and the percentages used to describe parts of data sets we underlined the former throughout this paper.) The best rule comprises an A/U at positions 10 and 19, a G/C at position 1, and more than three A/Us between positions 13 and 19, in the sense strand of the siRNA sequence. Using these rules, there is a 99.9% chance of designing an effective siRNA in a set of three with more than 50% knockdown efficiency in a biological readout.

A new synthesis of the hexasaccharide MBr1 antigen (globo-H) is reported. A revised construction with improved efficiency was necessary because an anti-cancer vaccine containing this antigen is entering phase II and phase III clinical trials for prostate cancer. The key feature of this second generation synthesis is the preparation of globo-H as its n-pentenyl glycoside. This group serves as an anomeric protecting group and as a linker for bioconjugation to carrier protein. The resultant synthesis allows for the production of suitable quantities of globo-H for clinical trials.

Three analogues of thiazole-4-carboxamide adenine dinucleotide (TAD) (1-3) containing a fluorine atom at the C2' of the adenine nucleoside (in the ribo and arabino configuration) and at the C3' (in the ribo configuration) were synthesized in high yield from the corresponding 5'-monophosphates of 2'-deoxy-2'-fluoroadenosine (9), 9-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)-adenine (17), and 3'-deoxy-3'-fluoroadenosine (14), respectively. Pure 2',3'-O-isopropylidene-tiazofurin 5'-phosphorimidazolide (8) was obtained by phosphorylation of the protected tiazofurin followed by treatment with carbonyldiimidazole and HPLC purification. Reaction of 8 with 9 in DMF-d7 (monitored by 1H and 31P NMR) afforded the desired dinucleotide 12, which after deisopropylidenation gave 1 in 82% yield. Small amounts of symmetrical dinucleotides AppA (10, 7.2%) and TRppTR (11, 8.0%) were also isolated during HPLC purification of the major product 12. In a similar manner, compounds 2 and 3 were obtained by coupling of 8 with 14 and 17 in 80% and 76% yield, respectively. All newly prepared fluoro-substituted compounds as well as beta-CF2-TAD, earlier synthesized by us, showed good inhibitory activity against inosine monophosphate dehydrogenase type II, the isozyme which is predominant in neoplastic cells. Binding of 1 (Kis = 0.5 microM), 2 (Kis = 0.7 microM), and 3 (Kis = 2.9 microM) was comparable to that of TAD (Ki = 0.2 microM). The difluoromethylene bisphosphonate analogue, beta-CF2-TAD (Ki = 0.17 microM), was found to be equally effective as the best cofactor-type inhibitor, beta-CH2-TAD (Ki = 0.11 microM). Interestingly, the level of inhibition of horse liver alcohol dehydrogenase by these compounds was found to be much lower (0.1 mM for 1 and 2 and no inhibition up to 10 mM for 3). These findings show that inhibition of tumor-induced inosine monophosphate dehydrogenase type II is selective and may be of therapeutic interest.