Synthesis of highly potent second-generation taxoids through effective kinetic resolution coupling of racemic beta-lactams with baccatins

Synthesis and biological evaluation of novel larotaxel analogues

Taxoids are a class of successful drugs and have been successfully used in chemotherapy for a variety of cancer types. However, despite the hope and promises that these taxoids have engendered, their utility is hampered by some clinic limitations. Extensive structure-activity relationship (SAR) studies of toxoids have been performed in many different laboratories. Whereas, SAR studies that based on the new-generation toxoid, larotaxel, have not been reported yet. In view of the advantages in preclinical and clinical data of larotaxel over former toxoids, new taxoids that strategicly modified at the C3'/C3'-N and C2 positions of larotaxel were designed, semi-synthesized, and examined for their potency and efficacy in vitro. As a result, it has been shown that the majority of these larotaxel analogues are exceptionally potent against both drug-sensitive tumor cells and tumor cells with drug resistance arising from P-glycoprotein over expression. Further in vivo antitumor efficacies investigations revealed A2 might be a potent antitumor drug candidate for further preclinical evaluation.

Linker technologies for antibody-drug conjugates

Antibody-drug conjugates (ADCs), which combine the specificity, favorable pharmacokinetics, and biodistribution of a monoclonal antibody (mAb) with the cytotoxic potency of a drug, are promising new therapies for cancer. Along with the development of monoclonal antibodies (mAbs) and cytotoxic drugs, the design of the linker is of essential importance, because it impacts the efficacy and tolerability of ADCs. The linker needs to provide sufficient stability during systemic circulation but allow for the rapid and efficient release of the cytotoxic drug in an active form inside the tumor cells. This review provides an overview of linker technologies currently used for ADCs and advances that have resulted in linkers with improved properties. Also provided is a brief summary of some considerations for the conjugation of antibody and drug linker such as drug-to-antibody ratio and site of conjugation.

Kinetic resolution of N-acyl-β-lactams via benzotetramisole-catalyzed enantioselective alcoholysis

The first nonenzymatic kinetic resolution of β-lactams has been achieved. Alcoholysis of their N-aroyl derivatives in the presence of a simple chiral acyl transfer catalyst, benzotetramisole, produces β-amino acid derivatives with excellent enantioselectivity.

Synthesis of docetaxel and butitaxel analogues through kinetic resolution of racemic beta-lactams with 7-O-triethylsilylbaccatin III

The kinetic resolution of racemic cis-4-phenyl- and cis-4-tert-butyl-3-hydroxy-beta-lactam derivatives with 7-O-triethylsilylbaccatin III yielded paclitaxel and butitaxel analogues with high diastereoselectivity. The results demonstrated that the tert-butyldimethylsilyl protecting group at the C3-hydroxy group of the beta-lactams provided optimum kinetic resolution in comparison with the sterically less demanding triethylsilyl group and the larger triisopropylsilyl group. In addition, it was found that the C4 beta-lactam substituents also influenced diastereoselectivity. The C4 tert-butyl-beta-lactams provided better diastereoselectivity than the corresponding C4 phenyl beta-lactams.

Efficiency in nonenzymatic kinetic resolution

The Walden memorial at the Technical University in Riga is pictured in the frontispiece to mark the recent centennial of the Walden inversion. This is a rare public monument to key events from the first era of exploration in stereocontrolled synthesis, and may be the only such monument to use the language of organic chemistry expressed at the molecular level. The reaction of racemic substrates with chiral nucleophiles is one of many methods currently known to achieve kinetic resolution, a phenomenon that ranks as the oldest and most general approach for the synthesis of highly enantioenriched substances. The first nonenzymatic kinetic resolutions as well as the original forms of the Walden inversion were studied in the 1890s. All of these investigations were conducted within the first generation following the demonstration that carbon is tetrahedral, and provided abundant evidence that the principles and importance of enantiocontrolled syntheses were understood. However, a reliable, rapid technique to quantify results and guide the optimization process was still lacking. Many decades passed before this problem was solved by the advent of HPLC and GLPC assays on chiral supports, which stimulated explosive growth in the synthesis of nonracemic substances by kinetic resolution. The Walden monument is accessible to passers-by for hands-on inspection as well as for contemplation and learning. In a similar way, kinetic resolution is experimentally accessible and can be thought-provoking at several levels. We follow the story of kinetic resolution from the early discoveries through fascinating historical milestones and conceptual developments, and close with a focus on modern techniques that maximize efficiency.

Recent advances in tumor-targeting anticancer drug conjugates

Traditional cancer chemotherapy relies on the premise that rapidly proliferating cancer cells are more likely to be a killed by cytotoxic agent. In reality, however, cytotoxic agents have very little or no specificity, which leads to systemic toxicity, causing severe undesirable side effects. Therefore, various drug delivery protocols and systems have been explored in the last three decades. Tumor cells overexpress many receptors and biomarkers, which can be used as targets to deliver cytotoxic agents into tumors. In general, a tumor-targeting drug delivery system consists of a tumor recognition moiety and a cytotoxic warhead connected directly or through a suitable linker to form a conjugate. The conjugate, which can be regarded as 'prodrug', should be systemically non-toxic. This means that the linker must be stable in circulation. Upon internalization into the cancer cell the conjugate should be readily cleaved to regenerate the active cytotoxic agent. Tumor-targeting conjugates bearing cytotoxic agents can be classified into several groups based on the type of cancer recognition moieties. This review describes recent advances in tumor-targeting drug conjugates including monoclonal antibodies, polyunsaturated fatty acids, folic acid, hyaluronic acid, and oligopeptides as tumor-targeting moieties.

Synthesis of novel optically pure β-lactams

Several new β-lactams were synthesized as racemates via a Staudinger reaction. The corresponding optically pure compounds were obtained in subsequent biotransformation steps either through baker's yeast reduction or lipase resolution. Their absolute configurations were established. The X-ray crystal structures of three new substituted β-lactams are reported here. These compounds represent key building blocks for a variety of medicinally important molecules, including inhibitors of aspartyl proteases and Taxol® analogues.Key words: optically pure β-lactams, lipase resolutions, baker's yeast reductions, Staudinger reaction.

The discovery of BMS-275183: an orally efficacious novel taxane

The evolution of 2, a C-4-methylcarbonate analogue of paclitaxel with minimal oral bioavailability and oral efficacy, into its C-3'-t-butyl-3'-N-t-butyloxycarbonyl analogue (15i), a novel taxane with oral efficacy in preclinical models that is comparable to iv administered paclitaxel, is described.

Baker’s yeast-catalyzed synthesis of optically pure 4-tert-butyl-3-hydroxy beta-lactam cis-(3R,4S) and trans-(3R,4R) diastereomers

Baker's yeast (Saccharomyces cerevisiae) reductions were applied to the synthesis of the paclitaxel C-13 side-chain analogue. An easily synthesized alpha-keto-beta-lactam (1-(4-methoxyphenyl)-4-tert-butylazetidin-2,3-dione, 4) was reduced by yeast cells to give a mixture of enantiomerically pure cis and trans isomers. Both compounds were isolated and characterized, and their absolute configurations were confirmed by X-ray crystallographic analysis.Key words: Taxol®, C-13 side-chain, paclitaxel analogues, optically pure alpha-hydroxy-beta-lactams, baker's yeast-catalyzed reductions.

Novel molecules that interact with microtubules and have functional activity similar to Taxol

Taxol is an antitumor drug approved by the FDA for the treatment of ovarian, breast and non-small-cell lung carcinomas. Originally isolated from the bark of the Pacific yew, Taxus brevifolia, it was the first natural product described that stabilized microtubules. In the past five years, a group of novel natural products, including the epothilones, discodermolide, eleutherobin, sarcodictyins and the laulimalides, all of which have biological activities similar to those of Taxol, has been discovered. In this review, we discuss each of these novel microtubule-stabilizing agents and the search for a common pharmacophore among them, taking into consideration recent advances in our understanding of the taxanes and tubulin.