ABSTRACT
Antibody-drug conjugates (ADCs) have begun to fulfil their promise as targeted cancer therapeutics with ten clinical approvals to date. As the field matures, much attention has focused upon the key factors required to produce safe and efficacious ADCs. Recently the role that linker-payload reagent design has on the properties of ADCs has been highlighted as an important consideration for developers. We have investigated the effect of incorporating hydrophilic macrocycles into reagent structures on the in vitro and in vivo behavior of ADCs. Bis-sulfone based disulfide rebridging reagents bearing Val-Cit-PABC-MMAE linker-payloads were synthesized with a panel of cyclodextrins and crown ethers integrated into their structures via a glutamic acid branching point. Brentuximab was selected as a model antibody and ten ADCs with a drug-to-antibody ratio (DAR) of 4 were prepared for biological evaluation. In vitro, the ADCs prepared showed broadly similar potency (range: 16-34 pM) and were comparable to Adcetris® (16 pM). In vivo, the cyclodextrin containing ADCs showed greater efficacy than Adcetris® and the most efficacious variant (incorporating a 3'-amino-α-cyclodextrin component) matched a 24-unit poly(ethylene glycol) (PEG) containing comparator. The ADCs bearing crown ethers also displayed enhanced in vivo efficacy compared to Adcetris®, the most active variant (containing a 1-aza-42-crown-14 macrocycle) was superior to an analogous ADC with a larger 24-unit PEG chain. In summary, we have demonstrated that hydrophilic macrocycles can be effectively incorporated into ADC reagent design and offer the potential for enhanced alternatives to established drug-linker architectures.
ABSTRACT
A wide range of diseases have been shown to be influenced by the accumulation of senescent cells, from fibrosis to diabetes, cancer, Alzheimer's and other age-related pathologies. Consistent with this, clearance of senescent cells can prolong healthspan and lifespan in in vivo models. This provided a rationale for developing a new class of drugs, called senolytics, designed to selectively eliminate senescent cells in human tissues. The senolytics tested so far lack specificity and have significant off-target effects, suggesting that a targeted approach could be more clinically relevant. Here, we propose to use an extracellular epitope of B2M, a recently identified membrane marker of senescence, as a target for the specific delivery of toxic drugs into senescent cells. We show that an antibody-drug conjugate (ADC) against B2M clears senescent cells by releasing duocarmycin into them, while an isotype control ADC was not toxic for these cells. This effect was dependent on p53 expression and therefore more evident in stress-induced senescence. Non-senescent cells were not affected by either antibody, confirming the specificity of the treatment. Our results provide a proof-of-principle assessment of a novel approach for the specific elimination of senescent cells using a second generation targeted senolytic against proteins of their surfaceome, which could have clinical applications in pathological ageing and associated diseases.
Subject(s)
Cellular Senescence/drug effects , Duocarmycins , Immunoconjugates , Senotherapeutics , beta 2-Microglobulin/metabolism , Cell Line , Duocarmycins/pharmacokinetics , Duocarmycins/pharmacology , Gene Expression Regulation/drug effects , Humans , Immunoconjugates/pharmacokinetics , Immunoconjugates/pharmacology , Senotherapeutics/pharmacokinetics , Senotherapeutics/pharmacology , Tumor Suppressor Protein p53/biosynthesisABSTRACT
Preparation of antibody-drug conjugates (ADCs) with a highly homogeneous drug loading in general requires site-selective conjugation of a cytotoxic payload. Typically, functionality utilized for attachment of the payload is achieved through engineering of suitable chemical handles or by enzymatic modification of the antibody. Relatively few methods to produce ADCs with homogeneous drug loading via endogenous amino acid conjugation have been developed. Herein we describe a robust method for the conjugation of antibodies using a cysteine rebridging approach to produce ADCs with highly homogeneous drug-to-antibody ratios (DAR) at the native interchain disulfides, called ThioBridge®. The process described relies upon an elegant cascade of addition-elimination reactions carried out under mild aqueous conditions that can be readily applied to wild-type antibodies without the need for prior modification via recombinant or enzymatic means. Using this method, conversions to a conserved DAR ADC are typically in the range of 70-95% and overall process yields of >70% are readily achieved.
Subject(s)
Antibodies, Monoclonal/chemistry , Cysteine/chemistry , Drug Development , Immunoconjugates/chemistry , Antibodies, Monoclonal, Humanized/chemistry , Chromatography , Disulfides/chemistry , Humans , Hydrophobic and Hydrophilic Interactions , Immunoconjugates/isolation & purification , Immunoconjugates/pharmacology , Structure-Activity RelationshipABSTRACT
Single domain antibodies that combine antigen specificity with high tissue penetration are an attractive alternative to conventional antibodies. However, rapid clearance from the bloodstream owing to their small size can be a limitation of therapeutic single domain antibodies. Here, we describe and evaluate the conjugation of a single domain i-body, AD-114, which targets CXCR4, to a panel of half-life extension technologies including a human serum albumin-binding peptide, linear and branched PEG, and PASylation (PA600). The conjugates were assessed in murine, rat and cynomolgus monkey pharmacokinetic studies and showed that the branched PEG was most effective at extending circulating half-life in mice; however, manufacturing limitations of PEGylated test material precluded scale-up and assessment in larger animals. PA600, by comparison, was amenable to scale-up and afforded considerable half-life improvements in mice, rats and cynomolgus monkeys. In mice, the circulating half-life of AD-114 was extended from 0.18 h to 7.77 h following conjugation to PA600, and in cynomolgus monkeys, the circulating half-life of AD-114-PA600 was 24.27 h. AD-114-PA600 was well tolerated in cynomolgus monkeys at dose rates up to 100 mg/kg with no mortalities or drug-related clinical signs.
Subject(s)
Bioengineering/methods , Polyethylene Glycols/chemistry , Receptors, CXCR4/immunology , Single-Domain Antibodies/pharmacology , Alanine/chemistry , Animals , Half-Life , Humans , Macaca fascicularis , Male , Mice , Mice, Inbred ICR , Pharmacokinetics , Proline/chemistry , Rats , Rats, Sprague-Dawley , Single-Domain Antibodies/chemistryABSTRACT
Antibody-drug conjugates (ADCs) are a promising class of anticancer agents which have undergone substantial development over the past decade and are now achieving clinical success. The development of novel site-specific conjugation technologies enables the systematic study of architectural features within the antibody conjugated drug linker that may affect overall therapeutic indices. Here we describe the results of a systematic study investigating the impact of drug-linker design on the in vivo properties of a series of homogeneous ADCs with a conserved site of conjugation, a monodisperse drug loading, a lysosomal release functionality and monomethyl auristatin E as a cytotoxic payload. The ADCs, which differed only in the relative position of certain drug-linker elements within the reagent, were first evaluated in vitro using anti-proliferation assays and in vivo using mouse pharmacokinetics (PK). Regardless of the position of a discrete polymer unit, the ADCs showed comparable in vitro potencies, but the in vivo PK properties varied widely. The best performing drug-linker design was further used to prepare ADCs with different drug loadings of 4, 6 and 8 drugs per antibody and compared to Adcetris® in a Karpas-299 mouse xenograft model. The most efficacious ADC showed complete tumor regression and 10/10 tumor free survivors at a single 0.5mg/kg dose. This study revealed drug-linker design as a critical parameter in ADC development, with the potential to enhance ADC in vivo potency for producing more efficacious ADCs.
Subject(s)
Antineoplastic Agents , Immunoconjugates , Oligopeptides , Animals , Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacokinetics , Antineoplastic Agents/therapeutic use , Cell Line, Tumor , Drug Design , Humans , Immunoconjugates/chemistry , Immunoconjugates/pharmacokinetics , Immunoconjugates/therapeutic use , Immunoglobulin G/chemistry , Immunoglobulin G/therapeutic use , Ki-1 Antigen/immunology , Mice, SCID , Neoplasms/drug therapy , Neoplasms/pathology , Oligopeptides/chemistry , Oligopeptides/pharmacokinetics , Oligopeptides/therapeutic use , Polyethylene Glycols/chemistry , Tumor Burden/drug effects , Xenograft Model Antitumor AssaysABSTRACT
Antibody Drug Conjugates (ADCs) use targeting ability of monoclonal antibodies to deliver potent cytototoxic payloads to their intended target. The linker encompasses a conjugating functionality suitable for attachment to the antibody, a spacer unit that typically incorporates a hydrophilic element and a trigger which releases the potent cytototoxic warhead. Understanding the conflicting requirements of ADC design, providing stability in systemic circulation but efficient payload release once the ADC reaches its intended target, is crucial to effective linker development. ADC linker design has been approached in a variety of different ways, with increasingly elegant solutions continuing to be reported as understanding of the intricate design complexities increases. This review focuses on the synthetic approaches used in ADC linkers, and the impact of linker design on antibody conjugation, ADC pharmacokinetics and payload release. Linker approaches utilized in commercial ADCs as well as ADCs currently in clinical, pre-clinical and early stage development are discussed.
Subject(s)
Antibodies, Monoclonal/immunology , Drug Design , Immunoconjugates/chemistry , Immunoconjugates/immunology , Antibodies, Monoclonal/chemistry , Antibodies, Monoclonal/pharmacokinetics , Humans , Immunoconjugates/pharmacokineticsABSTRACT
The conjugation of monomethyl auristatin E (MMAE) to trastuzumab using a reduction bis-alkylation approach that is capable of rebridging reduced (native) antibody interchain disulfide bonds has been previously shown to produce a homogeneous and stable conjugate with a drug-to-antibody ratio (DAR) of 4 as the major product. Here, we further investigate the potency of the DAR 4 conjugates prepared by bis-alkylation by comparing to lower drug loaded variants to maleimide linker based conjugates possessing typical mixed DAR profiles. Serum stability, HER2 receptor binding, internalization, in vitro potency, and in vivo efficacy were all evaluated. Greater stability compared with maleimide conjugation was observed with no significant decrease in receptor/FcRn binding. A clear dose-response was obtained based on drug loading (DAR) with the DAR 4 conjugate showing the highest potency in vitro and a much higher efficacy in vivo compared with the lower DAR conjugates. Finally, the DAR 4 conjugate demonstrated superior efficacy compared to trastuzumab-DM1 (T-DM1, Kadcyla), as evaluated in a low HER2 expressing JIMT-1 xenograft model.
Subject(s)
Cysteine/chemistry , Immunoconjugates/pharmacokinetics , Immunoconjugates/therapeutic use , Mammary Neoplasms, Experimental/drug therapy , Trastuzumab/chemistry , Animals , Cell Line, Tumor , Female , Humans , Immunoconjugates/chemistry , Mice , Xenograft Model Antitumor AssaysABSTRACT
To improve both the homogeneity and the stability of ADCs, we have developed site-specific drug-conjugating reagents that covalently rebridge reduced disulfide bonds. The new reagents comprise a drug, a linker, and a bis-reactive conjugating moiety that is capable of undergoing reaction with both sulfur atoms derived from a reduced disulfide bond in antibodies and antibody fragments. A disulfide rebridging reagent comprising monomethyl auristatin E (MMAE) was prepared and conjugated to trastuzumab (TRA). A 78% conversion of antibody to ADC with a drug to antibody ratio (DAR) of 4 was achieved with no unconjugated antibody remaining. The MMAE rebridging reagent was also conjugated to the interchain disulfide of a Fab derived from proteolytic digestion of TRA, to give a homogeneous single drug conjugated product. The resulting conjugates retained antigen-binding, were stable in serum, and demonstrated potent and antigen-selective cell killing in in vitro and in vivo cancer models. Disulfide rebridging conjugation is a general approach to prepare stable ADCs, which does not require the antibody to be recombinantly re-engineered for site-specific conjugation.
Subject(s)
Antibodies, Monoclonal, Humanized/chemistry , Antibodies, Monoclonal, Humanized/pharmacology , Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacology , Disulfides/chemistry , Oligopeptides/chemistry , Oligopeptides/pharmacology , Antineoplastic Agents/chemical synthesis , Cell Line, Tumor , Cell Proliferation/drug effects , Cell Survival/drug effects , Dose-Response Relationship, Drug , Drug Screening Assays, Antitumor , Humans , MCF-7 Cells , Molecular Structure , Structure-Activity Relationship , TrastuzumabABSTRACT
Quadruplexes DNA are present in telomeric DNA as well as in several cancer-related gene promoters and hence affect gene expression and subsequent biological processes. The conformations of G4 provide selective recognition sites for small molecules and thus these structures have become important drug-design targets for cancer treatment. The DNA G-quadruplex binding pentacyclic acridinium salt RHPS4 (1) has many pharmacological attributes of an ideal telomere-targeting agent but has undesirable off-target liabilities. Notably a cardiovascular effect was evident in a guinea pig model, manifested by a marked and sustained increase in QTcB interval. In accordance with this, significant interaction with the human recombinant ß2 adrenergic receptor, and M1, M2 and M3 muscarinic receptors was observed, together with a high inhibition of the hERG tail current tested in a patch clamp assay. Two related pentacyclic structures, the acetylamines (2) and (3), both show a modest interaction with ß2 adrenergic receptor, and do not significatively inhibit the hERG tail current while demonstrating potent telomere on-target properties comparing closely with 1. Of the two isomers, the 2-acetyl-aminopentacycle (2) more closely mimics the overall biological profile of 1 and this information will be used to guide further synthetic efforts to identify novel variants of this chemotype, to maximize on-target and minimize off-target activities. Consequently, the improvement of toxicological profile of these compounds could therefore lead to the obtainment of suitable molecules for clinical development offering new pharmacological strategies in cancer treatment.
Subject(s)
Acridines/chemistry , Acridines/pharmacology , G-Quadruplexes , Telomere/metabolism , Acridines/chemical synthesis , Animals , Cell Proliferation/drug effects , Cells, Cultured , Guinea Pigs , Humans , Ligands , Telomerase/antagonists & inhibitorsABSTRACT
Analogues of (dibenzo[b,d]thiophen-4-yl)-2-morpholino-4H-chromen-4-one (NU7441), a potent inhibitor of DNA-dependent protein kinase (DNA-PK; IC50 = 42 ± 2 nM), have been synthesized in which water-solubilizing groups [NHCO(CH2)nNR¹R², where n = 1 or 2 and the moiety R¹R²N was derived from a library of primary and secondary amines, e.g., morpholine] were placed at the 1-position. Several of the newly synthesized compounds exhibited high potency against DNA-PK and potentiated the cytotoxicity of ionizing radiation (IR) in vitro 10-fold or more (e.g., 2-(4-ethylpiperazin-1-yl)-N-(4-(2-morpholino-4-oxo-4H-chromen-8-yl)dibenzo[b,d]thio-phen-1-yl)acetamide, 39; DNA-PK IC50 = 5.0 ± 1 nM, IR dose modification ratio = 13). Furthermore, 39 was shown to potentiate not only IR in vitro but also DNA-inducing cytotoxic anticancer agents, both in vitro and in vivo. Counter-screening against other members of the phosphatidylinositol 3-kinase (PI-3K) related kinase (PIKK) family unexpectedly revealed that some of the compounds were potent mixed DNA-PK and PI-3K inhibitors.
Subject(s)
DNA-Activated Protein Kinase/antagonists & inhibitors , Morpholines/pharmacology , Phosphoinositide-3 Kinase Inhibitors , Protein Kinase Inhibitors/pharmacology , HeLa Cells , Humans , Morpholines/chemistryABSTRACT
Following the discovery of dibenzo[b,d]thiophen-4-yl)-2-morpholino-4H-chromen-4-one (NU7441) ( Leahy , J. J. J. ; Golding , B. T. ; Griffin , R. J. ; Hardcastle , I. R. ; Richardson , C. ; Rigoreau , L. ; Smith , G. C. M. Bioorg. Med. Chem. Lett. 2004 , 14 , 6083 - 6087) as a potent inhibitor (IC50 = 30 nM) of DNA-dependent protein kinase (DNA-PK), we have investigated analogues in which the chromen-4-one core template has been replaced by aza-heterocyclic systems: 9-substituted 2-morpholin-4-ylpyrido[1,2-a]pyrimidin-4-ones and 8-substituted 2-morpholin-4-yl-1H-quinolin-4-ones. The 8- and 9-substituents were either dibenzothiophen-4-yl or dibenzofuran-4-yl, which were each further substituted at the 1-position with water-solubilizing groups [NHCO(CH2)(n)NR¹R², where n = 1 or 2 and the moiety R¹R²N was derived from a library of primary and secondary amines (e.g., morpholine)]. The inhibitors were synthesized by employing a multiple-parallel approach in which the two heterocyclic components were assembled by Suzuki-Miyaura cross-coupling. Potent DNA-PK inhibitory activity was generally observed across the compound series, with structure-activity studies indicating that optimal potency resided in pyridopyrimidin-4-ones bearing a substituted dibenzothiophen-4-yl group. Several of the newly synthesized compounds (e.g., 2-morpholin-4-yl-N-[4-(2-morpholin-4-yl-4-oxo-4H-pyrido[1,2-a]pyrimidin-9-yl)dibenzothiophen-1-yl]acetamide) combined high potency against the target enzyme (DNA-PK IC50 = 8 nM) with promising activity as potentiators of ionizing radiation-induced cytotoxicity in vitro.
Subject(s)
Benzopyrans/chemistry , DNA-Activated Protein Kinase/antagonists & inhibitors , Pyridines/chemical synthesis , Pyrimidinones/chemical synthesis , Quinolones/chemical synthesis , Cell Membrane Permeability , DNA Damage/drug effects , DNA Damage/radiation effects , Furans/chemical synthesis , Furans/chemistry , Furans/pharmacology , HeLa Cells , Humans , Pyridines/chemistry , Pyridines/pharmacology , Pyrimidinones/chemistry , Pyrimidinones/pharmacology , Quinolones/chemistry , Quinolones/pharmacology , Small Molecule Libraries , Structure-Activity Relationship , Thiophenes/chemical synthesis , Thiophenes/chemistry , Thiophenes/pharmacologyABSTRACT
Ataxia telangiectasia (A-T) mutated (ATM) is critical for cell cycle checkpoints and DNA repair. Thus, specific small molecule inhibitors targeting ATM could perhaps be developed into efficient radiosensitizers. Recently, a specific inhibitor of the ATM kinase, KU-55933, was shown to radiosensitize human cancer cells. Herein, we report on an improved analogue of KU-55933 (KU-60019) with K(i) and IC(50) values half of those of KU-55933. KU-60019 is 10-fold more effective than KU-55933 at blocking radiation-induced phosphorylation of key ATM targets in human glioma cells. As expected, KU-60019 is a highly effective radiosensitizer of human glioma cells. A-T fibroblasts were not radiosensitized by KU-60019, strongly suggesting that the ATM kinase is specifically targeted. Furthermore, KU-60019 reduced basal S473 AKT phosphorylation, suggesting that the ATM kinase might regulate a protein phosphatase acting on AKT. In line with this finding, the effect of KU-60019 on AKT phosphorylation was countered by low levels of okadaic acid, a phosphatase inhibitor, and A-T cells were impaired in S473 AKT phosphorylation in response to radiation and insulin and unresponsive to KU-60019. We also show that KU-60019 inhibits glioma cell migration and invasion in vitro, suggesting that glioma growth and motility might be controlled by ATM via AKT. Inhibitors of MEK and AKT did not further radiosensitize cells treated with KU-60019, supporting the idea that KU-60019 interferes with prosurvival signaling separate from its radiosensitizing properties. Altogether, KU-60019 inhibits the DNA damage response, reduces AKT phosphorylation and prosurvival signaling, inhibits migration and invasion, and effectively radiosensitizes human glioma cells.
Subject(s)
Cell Movement , Extracellular Signal-Regulated MAP Kinases/metabolism , Glioma/drug therapy , Glioma/enzymology , Insulin/metabolism , Morpholines/therapeutic use , Protein Kinase Inhibitors/therapeutic use , Proto-Oncogene Proteins c-akt/metabolism , Thioxanthenes/therapeutic use , Ataxia Telangiectasia/enzymology , Ataxia Telangiectasia/pathology , Ataxia Telangiectasia Mutated Proteins , Cell Cycle Proteins/antagonists & inhibitors , Cell Cycle Proteins/metabolism , Cell Movement/drug effects , Cell Movement/radiation effects , Cell Survival/drug effects , Cell Survival/radiation effects , DNA-Binding Proteins/antagonists & inhibitors , DNA-Binding Proteins/metabolism , Fibroblasts/drug effects , Fibroblasts/enzymology , Fibroblasts/radiation effects , Gamma Rays , Glioma/pathology , Humans , Insulin/pharmacology , MAP Kinase Signaling System/drug effects , MAP Kinase Signaling System/radiation effects , Morpholines/chemistry , Morpholines/pharmacology , Neoplasm Invasiveness , Phosphoserine/metabolism , Protein Kinase Inhibitors/chemistry , Protein Kinase Inhibitors/pharmacology , Protein Serine-Threonine Kinases/antagonists & inhibitors , Protein Serine-Threonine Kinases/metabolism , Pyrones/chemistry , Pyrones/pharmacology , Radiation-Sensitizing Agents/pharmacology , Radiation-Sensitizing Agents/therapeutic use , Thioxanthenes/chemistry , Thioxanthenes/pharmacology , Tumor Suppressor Proteins/antagonists & inhibitors , Tumor Suppressor Proteins/metabolismABSTRACT
The synthesis and biological evaluation of libraries of 8-biarylchromen-4-ones enabled the elucidation of structure-activity relationships for inhibition of the DNA-dependent protein kinase (DNA-PK), with 8-(3-(thiophen-2-yl)phenyl)chromen-4-one and 8-(3-(thiophen-3-yl)phenyl)chromen-4-one being especially potent inhibitors.
Subject(s)
Chromones/chemistry , Chromones/pharmacology , DNA-Activated Protein Kinase/antagonists & inhibitors , Protein Kinase Inhibitors/chemistry , Protein Kinase Inhibitors/pharmacology , Chromones/chemical synthesis , HeLa Cells , Humans , Protein Kinase Inhibitors/chemical synthesis , Radiation-Sensitizing Agents/chemical synthesis , Radiation-Sensitizing Agents/chemistry , Radiation-Sensitizing Agents/pharmacology , Structure-Activity RelationshipABSTRACT
Structure-activity relationships have been investigated for inhibition of DNA-dependent protein kinase (DNA-PK) and ATM kinase by a series of pyran-2-ones, pyran-4-ones, thiopyran-4-ones, and pyridin-4-ones. A wide range of IC50 values were observed for pyranones and thiopyranones substituted at the 6-position, with the 3- and 5-positions proving intolerant to substitution. Related pyran-2-ones, pyran-4-ones, and thiopyran-4-ones showed similar IC50 values against DNA-PK, whereas the pyridin-4-one system proved, in general, ineffective at inhibiting DNA-PK. Extended libraries exploring the 6-position of 2-morpholino-pyran-4-ones and 2-morpholino-thiopyrano-4-ones identified the first highly potent and selective ATM inhibitor 2-morpholin-4-yl-6-thianthren-1-yl-pyran-4-one (151C; ATM; IC50=13 nM) and revealed constrained SARs for ATM inhibition compared with DNA-PK. One of the most potent DNA-PK inhibitors identified, 2-(4-methoxyphenyl)-6-(morpholin-4-yl)pyran-4-one (16; DNA-PK; IC50=220 nM) effectively sensitized HeLa cells to the topoisomerase II inhibitor etoposide in vitro.
Subject(s)
Antineoplastic Agents/chemical synthesis , Cell Cycle Proteins/antagonists & inhibitors , DNA-Activated Protein Kinase/antagonists & inhibitors , DNA-Binding Proteins/antagonists & inhibitors , Morpholines/chemical synthesis , Phosphatidylinositol 3-Kinases/chemistry , Protein Serine-Threonine Kinases/antagonists & inhibitors , Pyrans/chemical synthesis , Pyridones/chemical synthesis , Pyrones/chemical synthesis , Tumor Suppressor Proteins/antagonists & inhibitors , Antineoplastic Agents/chemistry , Antineoplastic Agents/pharmacology , Ataxia Telangiectasia Mutated Proteins , Cell Cycle Proteins/chemistry , Combinatorial Chemistry Techniques , DNA-Binding Proteins/chemistry , Etoposide/pharmacology , HeLa Cells , Humans , Morpholines/chemistry , Morpholines/pharmacology , Protein Serine-Threonine Kinases/chemistry , Pyrans/chemistry , Pyrans/pharmacology , Pyridones/chemistry , Pyridones/pharmacology , Pyrones/chemistry , Pyrones/pharmacology , Structure-Activity Relationship , Topoisomerase II Inhibitors , Tumor Suppressor Proteins/chemistryABSTRACT
A new enantioselective synthesis of Masamune's AB fragment (1) for bryostatin 7 is described. Key steps in the new route include a Meerwein-Ponndorf-Verley reduction to set the O(7) stereocenter and an alkylative union between the dithiane 6 and iodide 5 to construct the C(9)-C(10) bond. Because we have previously published a synthesis of Masamune's C-ring phenyl sulfone 2, our new route to 1 constitutes a formal total synthesis of bryostatin 7; it also corrects the previously reported spectral data for 1 in CDCl3.
Subject(s)
Antineoplastic Agents/chemical synthesis , Macrolides/chemical synthesis , Antineoplastic Agents/chemistry , Bryostatins , Macrolides/chemistry , StereoisomerismABSTRACT
[structure: see text] The synthesis of two truncated bryostatin analogues 2 and 3 is described. High-field NMR measurements on the C-ring analogue 3 in C(2)H(3)CN containing 25% (2)H(2)O have shown that it binds to the CRD2 of human PKC-alpha at virtually the same position as phorbol-13-acetate (PA) and bryostatin 1 (1). NMR titration studies have also revealed that 3 binds to the CRD2 with a potency similar in magnitude to PA but much less potently than 1.
Subject(s)
Antineoplastic Agents/chemistry , Lactones/chemistry , Protein Kinase C/chemistry , Antineoplastic Agents/metabolism , Binding Sites , Bryostatins , Humans , Lactones/metabolism , Macrolides , Nuclear Magnetic Resonance, Biomolecular , Phorbol Esters , Protein Binding , Protein Kinase C/metabolism , Protein Kinase C-alpha , Structure-Activity Relationship , TitrimetryABSTRACT
[reaction: see text] The "Southern Hemisphere" intermediate 2, used by Masamune and co-workers for their asymmetric total synthesis of bryostatin 7 (1), has been synthesized from (E)-1,4-hexadiene (11) by a 24-step pathway that has a longest linear sequence of only 20 steps. This is the shortest synthesis of 2 so far recorded, and moreover, it is fully stereocontrolled.
Subject(s)
Antineoplastic Agents/chemical synthesis , Lactones/chemical synthesis , Alkenes , Bryostatins , Lactones/chemistry , Macrolides , Organometallic CompoundsABSTRACT
This review summarises the main developments that have occurred in bryostatin chemistry over the period 1982 to 2001 and has 117 references.
Subject(s)
Antineoplastic Agents , Lactones/chemistry , Lactones/chemical synthesis , Macrolides , Bryostatins , Catalysis , Cyclization , Humans , Models, Molecular , Molecular Structure , StereoisomerismABSTRACT
[reaction: see text] A biosynthetic proposal for ring formation in the antitumor agent halichomycin is presented in which macrocyclization of the putative prehalichomycin intermediate 1 is the first step. Compound 2 then undergoes dehydration to the alpha-keto N-acylimine 3 followed by tandem nucleophilic addition of the C(16)-hydroxyl to form the hemimacrolactam. A stereospecific Michael ring closure and enol protonation complete C-ring assembly. So far, synthetic efforts toward 1 have resulted in 8.