Base-catalyzed isomerization of retinoic acid. Synthesis and differentiation-inducing activities of 14-alkylated all-trans-, 13-cis-, and 20,14-retro-retinoic acids

Exploratory Chemistry toward the Identification of a New Class of Multidrug Resistance Reverters Inspired by Pervilleine and Verapamil Models

On the basis of the present knowledge of the substrate recognition site of ABC transporter proteins and inspired by the structures of verapamil and pervilleine A, a new class of Pgp-mediated multidrug resistance (MDR) reverters has been designed and synthesized. The new compounds are flexible molecules carrying one or two basic nitrogen atoms flanked, at properly modulated distance, by two aromatic moieties. Most of the molecules studied possess MDR inhibitory activity on anthracycline-resistant erythroleukemia K 562 cells, showing a potency that is higher than that of the reference compound verapamil and, in a few cases (7, 12, 13,17, 20, 22, 28), is in the high nanomolar range. These compounds may be useful leads to develop new MDR reverting agents. In fact, the chemical structure of the class is fairly simple and can be implemented in a variety of ways that will allow the synthesis of new compounds that might be useful leads for the development of drugs to control Pgp-dependent MDR.

Determination of endogenous levels of retinoic acid isomers in type II diabetes mellitus patients. Possible correlation with HbA1c values

A sensitive HPLC method for simultaneous determination of endogenous levels of all-trans-(ATRA), 13-cis-(13cRA), and 9-cis-retinoic acids (9cRA) was applied to serum samples from healthy volunteers and type II diabetes mellitus patients. Levels of 9cRA (around 0.2 ng/ml in both groups) were below the limit of quantification. The concentrations of ATRA and 13cRA were reliably quantified, and the within-day and between-days variances indicated that they were well maintained with little variation. Concentrations of serum ATRA and 13cRA of diabetic patients (ATRA: 1.76 +/- 0.54 ng/ml; 13cRA: 1.77 +/- 0.39ng/ml, n=13) were rather lower than those of healthy subjects (ATRA: 2.08 +/- 0.53 ng/ml; 13cRA: 2.05 +/- 0.26 ng/ml, n = 18), but the differences were not significant, except for the sum of ATRA and 13cRA (p = 0.033). Interestingly, the serum levels of retinoic acids in diabetic patients correlated positively with the hemoglobin A1c (HbA1c) values (ATRA: r = 0.57, p < 0.05; 13cRA: r = 0.62, p < 0.05). The results warrant further studies on the possible involvement of uncontrolled serum retinoic acids levels in the pathogenesis and/or treatment of diabetes mellitus.

Design and synthesis of a cephalosporin-retinoic acid prodrug activated by a monoclonal antibody-beta-lactamase conjugate

Two novel series of all-trans-beta-retinoic acid derivatives were synthesized and found to possess anticancer activity. The first series, cephalosporin 3'-retinoic esters 6 and 7 were, respectively, obtained by the condensation of all-trans-beta-retinoic acid (2) with cephalosporins 4 and 5. The second series, 7-(retinamido)cephalosporins 11 and 12, were synthesized, respectively, by the condensation of 2 with cephalosporins 9 and 10. These four heretofore undescribed compounds 6, 7, 11, and 12 showed inhibitory activity against murine leukemias (L1210 and P388), sarcoma 180, breast carcinoma (MCF7), and human T-lymphocytes (Molt4/C8 and CEM/0). They also inhibited squamous metaplasia and keratinization in tracheal organ cultures derived from vitamin-A-deficient hamsters. Moreover, cephalosporin 3'-retinoic ester 7 exhibited enhanced activity against keratinization with ED(50)=3.91 x 10(-11) M in the presence of a beta-lactamase from Staphylococcus aureus 95. A tumor targeting fusion protein (dsFv3-beta-lactamase) was also used in conjunction with cephem-based retinoid 7 and the potency of 7 toward L1210, P388, and MCF7 was found to approach that of the free retinoic acid (2). In the presence of dsFv3-beta-lactamase, tumor cells were found to be much more susceptible to retinoid 7 than normal human embryonic lung cells. These notions provide a new approach to the use of beta-retinoic acid for antitumor therapy.

A Novel Method for a Stereoselective Synthesis of Trisubstituted Olefin Using Tricarbonyliron Complex: A Highly Stereoselective Synthesis of (all-E)- and (9Z)-Retinoic Acids

In order to establish the stereoselective synthesis of retinoic acids, which are ligand molecules of the retinoic acid receptors (RARs, all-E-isomer) and the retinoid X receptors (RXRs, 9Z-isomer), the reaction of beta-ionone-tricarbonyliron complex 7 with carbanions was investigated. Treatment of 7 with the lithium salt of acetonitrile afforded (7E,9E)-beta-ionylideneacetonitrile-tricarbonyliron complex 8 exclusively, via addition, dehydration, and migration of tricarbonyliron complex. On the contrary, the reaction of 7 with the lithium enolate of ethyl acetate and subsequent dehydration by thionyl chloride afforded the ethyl (7E,9Z)-beta-ionylideneacetate-tricarbonyliron complex 16b predominantly. These compounds (8 and 16b) were converted to the corresponding beta-ionylideneacetaldehyde-tricarbonyliron complexes (10 and 22) in excellent yields, respectively. The Emmons-Horner reaction of these compounds with C5-phosphonate followed by the sequence of decomplexation and alkaline hydrolysis gave the corresponding retinoic acids (26 and 29).

Differentiation-inducing activity of retinoic acid isomers and their oxidized analogs on human promyelocytic leukemia HL-60 cells

Retinoidal activity of retinoic acid isomers [all-trans-retinoic acid (ATRA), 9-cis-retinoic acid (9CRA) and 13-cis-retinoic acid (13CRA)] and their oxidized derivatives [19-hydroxy and 19-oxo derivatives of ATRA (19-hydroxy-ATRA and 19-oxo-ATRA), 19-oxo derivative of 9CRA (19-oxo-9CRA), and 19-hydroxy derivative of 13CRA (19-hydroxy-13CRA)] was evaluated by means of a human promyelocytic leukemia HL-60 cell differentiation induction assay. All the compounds examined showed this activity with ED50 values of 2-30 nM, which are in accordance with their binding activity to nuclear retinoic acid receptors (RARs).