Catalytic enantioselective synthesis of (14R)-14-hydroxy-4,14-retro-retinol from retinyl acetate

NAGAI M., YOSHIMURA H., HIBI S., KIKUCHI K., ABE S., ASADA M., YAMAUCHI T., HIDA T., HIGASHI S., HISHINUMA I., YAMANAKA T.

Practical and facile total syntheses of the remarkably unstable (R)-(+)-14-hydroxy-4, 14-retroretinol[(R)-14HRR] 1 and of its enantiomer 2 have been achieved via an acid-catalyzed dehydration reaction of the respective tetraeneol intermediates 10 and its enantiomer obtained from (R)-(+)-1,2-O-isopropylidene-butane-1,2,3-triol 3

Corey E.J., Guzman-Perez A., Noe M.C.

Kolb H.C., VanNieuwenhze M.S., Sharpless K.B.

Corey E.J., Noe M.C., Grogan M.J.

On the basis of ideas recently advanced regarding the origin of enantioselectivity in the OsO 4 -promoted dihydroxylation of olefins catalyzed by bis-cinchona alkaloid derivatives such as 1 , specifically strong evidence for reaction via transition state assembly 2 , the mono-quinidine derivative 3 was selected as a promising catalytic ligand. The experimental observation of high enantioselectivity promoted by 3 provides additional evidence in favor of transition-state 2 . Graphic

Corey E.J., Noe M.C., Sarshar S.

X-Ray crystallographic analysis on single crystals and 1H NMR studies in solution of various bis-cinchona alkaloid derivatives reveal a general preference for a conformation which possesses a U-shaped binding pocket with favorable dimensions for the inclusion of olefinic substrates and the acceleration of face selective dihydroxylation by a proximate pentacoordinate OsO4.

Derguini F., Nakanishi K., Haemmerling U., Buck J.

14-Hydroxy-4,14-retro-retinol (14-HRR), first isolated from cultures of lymphoblastoid 5/2 and HeLa cells and characterized by NMR, UV, and CD, is a metabolite of retinol which promotes growth of B lymphocytes in culture and activation of T lymphocytes by antigen receptor-mediated signals. It is also produced by various tested cell lines: fibroblasts, leukemia, and Drosophila cells. 14-HRR is the first bioactive retro-retinoid to be discovered and, after retinal and retinoic acid, is the third intracellular messenger molecule derived from retinol. Physical properties and intracellular signaling activities of synthetic (14R)-HRR, (14S)-HRR, and racemic 14-HRR are described. CD spectra indicate that natural 14-HRR isolated previously was a mixture of enantiomers. B-cell survival and T-cell activation assays performed in the optimal range of (7-1.6) x 10(-7) M surprisingly showed that all 14-HRR compounds exhibit similar activity, with the 14R enantiomer exhibiting slightly higher activity in comparison to the 14S enantiomer. However, because of the semiquantitative nature of the assays, the conclusion as to which enantiomer is more active and which is the true ligand for the target receptor must await characterization of this protein.

Eppinger T.M., Buck J., Hämmerling U.

Vitamin A (retinol) is a prohormone that exerts its pleiotropic biological effects after conversion into multiple metabolites. In this report we describe the identification of three endogenous, retinolderived effector molecules, 14-hydroxy-retro-retinol (14-HRR), anhydroretinol (AR), and retinoic acid (RA) and a putative storage form of retinol, retinylesters (RE) in the human promyelocytic leukemia cell line HL-60. Exogenous application of the retinol metabolites in retinol-depleted serum-free cultures of HL-60 allowed the identification of unique cellular functions for each metabolite: 14-HRR is a growth factor for HL-60. AR is a functional antagonist of 14-HRR with growth-inhibiting activity, and RA is a potent inducer of granulocyte differentiation accompanied by growth arrest. Finally, intracellular RE serves as storage form allowing continuous production of 14-HRR when no external retinol is available.

Corey E.J., Noe M.C.

Buck J., Grün F., Derguini F., Chen Y., Kimura S., Noy N., Hämmerling U.

Vitamin A (retinol) is an essential cofactor for growth of B lymphocytes in culture and for activation of T lymphocytes by antigen receptor-mediated signals. 14-hydroxy-4,14-retro-retinol (14-HRR) a metabolite of retinol, has been implicated as the intracellular mediator of this effect. Anhydroretinol (AR) is a retinol derivative with retro structure produced in activated human B lymphocytes and the insect cell lines SF 21 and Schneider S2. AR reversibly inhibits retinol- and 14-HRR-dependent effects and blocks B lymphocyte proliferation as well as activation of resting T lymphocytes. The intracellular signaling pathway blocked by AR in T cell activation is distinct from the calcineurin/interleukin 2 pathway inhibitable by cyclosporine A or FK-506.

Corey E.J., Noe M.C., Sarshar S.

Garbe A., Buck J., Hämmerling U.

Murine thymic T cells depleted of antigen-presenting cells proliferate poorly in response to crosslinking anti-CD3 monoclonal antibodies or concanavalin A when cultured in conventional fetal calf serum-containing serum. However, in a serum-free medium formulated to contain, in addition to basic ingredients, insulin, transferrin, albumin, linoleic acid (ITLB), and retinol, proliferation is vigorous. The presence of retinol is critical, because when omitted, cells do not become activated. The subsets of T cells proliferating with the assistance of retinol cofactor are both CD4+ and CD8+ thymic T cells, and CD4+ peripheral T cells. Mature CD8+ T cells of lymph nodes can also be activated in ITLB medium plus retinol, provided that interleukin 2 (IL-2) is added. Retinol needs to be present at the time when T cell receptor triggering is initiated, suggesting that early activation events (G0 to G1 transition) are dependent on retinol. It is currently less clear whether or not subsequent events associated with G1 to S phase transition also require the presence of retinol. 14-hydroxy-retroretinol (14HRR) is a metabolic product of retinol in lymphocytes, and this retinoid effectively supports T cell activation in conjunction with a mitogen in lieu of retinol. Thus, while retinol and its intracellular product, 14HRR, are unable to activate T cells on their own, they are important cofactors. The requirement for retinol in CD3-mediated T cell activation cannot be satisfied by retinoic acid or ILs-1, 2, 4, and 6, and tumor necrosis factor-alpha whereas interferon gamma can substitute for retinol. Our experiments are compatible with the idea that retinol, in the course of cellular activation, is converted to 14HRR, which is needed as intracellular messenger. If substantiated by molecular studies now underway, our data should lead to the description of a new signal pathway distinct from the retinoic acid signal pathway observed in nonlymphoid cells, but perhaps functioning by a similar mechanism, i.e., ligand-assisted transcriptional regulation.

Buck J., Derguini F., Levi E., Nakanishi K., Hämmerling U.

Buck J., Myc A., Garbe A., Cathomas G.

We have previously reported on the dependency of activated B lymphocytes for retinol. Here we confirm and extend these findings that cells deprived of retinol perish in cell culture within days, displaying neither signs of apoptosis nor of cell cycle arrest. Cell death can be prevented by physiological concentrations of retinol and retinal, but not by retinoic acid or three synthetic retinoic acid analogues. To exclude the possibility that retinoic acid is so rapidly degraded as to escape detection, we have tested its stability in intra- and extracellular compartments. Contrary to expectation, we find that retinoic acid persists for longer (t 1/2 3 d) in cultures than retinol (t 1/2 1 d). Furthermore, despite the use of sensitive trace-labeling techniques, we cannot detect retinoic acid or 3,4-didehydroretinoic acid among retinol metabolites. However, retinol is converted into several new retinoids, one of which has the ability to sustain B cell growth in the absence of an external source of retinol, supporting the notion of a second retinol pathway. We have also determined which of the known retinoid-binding proteins are expressed in B lymphoblastoid cells. According to results obtained with polymerase chain reaction-assisted mRNA detection, they transcribe the genes for cellular retinol- and cellular retinoic acid-binding proteins, for the nuclear retinoic acid receptors, RAR-alpha, -gamma, and RXR-alpha, but not RAR-beta. Our findings that B cells do not synthesize retinoic acid or respond to exogenous retinoic acid on the one hand, but on the other hand convert retinol to a novel bioactive form of retinol, suggest the existence of a second retinoid pathway, distinct from that of retinoic acids.

Buck J., Ritter G., Dannecker L., Katta V., Cohen S.L., Chait B.T., Hämmerling U.

When EBV-transformed human B cells are removed from conventional cell cultures, washed, and seeded at a low cell density in serum-free medium, their growth potential is greatly diminished. Fresh serum restores the growth of low density B cell cultures. We have traced this restorative effect to an essential factor present in the lipid fraction of serum and have identified it as all-trans retinol. The identification is based on the close similarities of the factor isolated from serum with authentic all-trans retinol as revealed by mass spectrometry, HPLC chromatography, and the ability to stimulate the growth of lymphoblastoid cells in the bioassay. Retinol is active at concentrations equal to its concentration in serum. Retinol is also a requirement for growth in suspension cultures at cell densities of 3 x 10(5)/ml. Cells removed at any time from such exponentially growing cultures and transferred to retinol-free medium cease to grow and consequently die, whereas in the continued presence of retinol, cell growth is unabated. All-trans retinal can substitute for retinol, but retinoic acid fails to stimulate the growth of lymphoblastoid cells at physiological concentrations. Normal human B lymphocytes also require retinol as a costimulator of proliferation after activation by anti-mu antibody or Staphylococcus aureus (Cowan strain) bacteria. In serum, retinol is bound to retinol-binding protein, which in turn forms a complex with prealbumin. Accordingly, we find that B cells respond to retinol bound to its physiological serum carrier, retinol-binding protein. In conclusion, human B cells are critically dependent for optimal growth in cell culture on an external supply of retinol.

Mitschke B., Turberg M., List B.

Summary Catalysis has fascinated scientists for centuries and is one of the main pillars of the modern world economy. Achieving high reactivity and selectivity is a crucial requirement of heterogeneous and homogeneous organic, metallic, and biological catalysts. Here, we highlight an underlying principle that is relevant to the reactivity and selectivity of all types of catalysts—"confinement," the shaping of a catalyst's active site. While this aspect has been well recognized within the fields of heterogeneous and enzymatic catalysis, and has been invoked in supramolecular systems, confinement has been less appreciated in the design of small-molecule catalysts. We identify confinement as a unifying element in the science of selective catalysis, reaching beyond the traditional boundaries of the individual subfields. A particular emphasis is given to the latest developments in the area of organocatalysis.

Álvarez R., Vaz B., Gronemeyer H., de Lera Á.R.

Leyva A., Blum F.E., Hewitt P.R., Ley S.V.

A new method for the synthesis of dienes and enynes containing chiral 1,2-diols is described. The strategy is based on the Pd-catalysed cross-coupling reactions of a series of vinyl and alkynyl asymmetric butanediacetal-protected building blocks. After the coupling, removal of the protecting group leads to the desired functionalised dienes and enynes.

Noe M.C., Letavic M.A., Snow S.L.

Abstract The oxidation of alkenes to vicinal diols using osmium tetroxide is one of the most selective and reliable transformations in organic synthesis. The reaction stereospecifically produces a cis‐1,2‐glycol and is tolerant of a wide array of functional groups. Methods have been developed to oxidize alkenes stoichiometrically, as well as in the presence of catalytic amounts of osmium tetroxide, when a suitable secondary oxidant is present. The latter process is particularly useful considering the expense and toxicity of osmium tetroxide. The utility of dihydroxylation in organic synthesis is enhanced by the facile transformations of the cis‐1,2‐diol products into other useful derivatives. Among the most versatile intermediates are the corresponding cyclic sulfates, which serve as reactive epoxide equivalents that can be used singly or doubly displaced with amine‐, oxygen‐, sulfur‐, or carbon‐based nucleophiles. The reaction of osmium tetroxide with alkenes is accelerated by several orders of magnitude in the presence of coordinating amine ligands such as triethylamine, quinuclidine, or diazobicyclooctane. The logical extension to asymmetric osmylation of alkenes in the presence of chiral amine bases spurred the study of asymmetric dihydroxylation. The breakthrough of catalytic turnover in the cinchona alkaloid‐osmium tetroxide system revolutionized the field of asymmetric dihydroxylation. Specialized ligands have been developed to provide position selectivity in the dihydroxylation of polyenes, efficient kinetic resolution of racemic substrates, and high levels of enantioselectivity for each of six alkene classes.

Alvarez S., Alvarez R., de Lera A.R.

The Stille cross-coupling of trienyliodide 4 and E-alkenylstannanes 5, derived from enantioenriched diols obtained by a Sharpless asymmetric dihydroxylation (SAD), provides a convergent route to all stereoisomers of 13,14-dihydroxyretinol (DHR), an immunomodulator derived from vitamin A.

Vakiani E., Buck J.

In a classic histological study published in 1925 Wolbach and Howe described the widespread pathology associated with vitamin A deficiency in rats. The reported abnormalities included stunted growth, blindness, keratinization of the epithelial linings of the respiratory and alimentary tracts, defective development of testis and atrophy of the central and peripheral lymphoid organs. Subsequent studies with vitamin A deficient animals have confirmed these findings and have established a critical role for retinol in the normal development and maintenance of most tissues.

Corey E.J., Noe M.C.

The Sharpless enantioselective dihydroxylation of terminal olefins by OsO4 using the catalytic chiral ligand (DHQD)2PYDZ (1) has been shown to follow Michaelis−Menten kinetics, demonstrating fast reversible formation of a complex of olefin, OsO4, and 1 prior to the rate-limiting conversion to the Os(VI) ester intermediate. There is a good correlation between the observed binding constants, Km, and the degree of enantioselectivity of the dihydroxylation indicating that van der Waals binding of the substrate by 1·OsO4 is important to enantioselective rate enhancement. Inhibition of the oxidation by various compounds has been demonstrated kinetically using Dixon analysis of the data, and Ki values have been determined and correlated with inhibitor structure. The strongest inhibitors are compounds with the ability to coordinate to Os(VIII) of the 1·OsO4 complex while simultaneously binding in the pocket formed by the aromatic subunits of the ligand. Parallelism between Km and Ki values and their relationship with structure indicate similar binding in the substrate and inhibitor complexes with 1·OsO4. The kinetic, structural, and stereochemical data, as summarized in Tables 1 and 3, support a mechanism for the enantioselective dihydroxylation which involves (1) rapid, reversible formation of an olefin-Os(VIII) π-d complex and (2) slow rearrangement to the [3 + 2] cycloaddition transition state which is exemplified in Figure 12. In terms of this mechanism, enantioselective acceleration is the result of two factors: (1) enzyme−substrate-like complexation which brings the reactants together in the appropriate geometry for further conversion to the predominating enantiomer, thereby providing a high effective reactant concentration (entropic effect) and (2) a driving force in the next step due to relief of eclipsing strain about the OsO4−N bond which lowers the activation enthalpy. Taken together with existing data on the Sharpless enantioselective dihydroxylation, the present results strongly support the [3 + 2] cycloaddition pathway and the U-shaped binding pocket which was advanced earlier.