Biomedical subjects

Mark McLaughlin

Publications and source records attributed to Mark McLaughlin.

12 recordsLinked to original sources

PubMed2007

PLP overexpression perturbs myelin protein composition and myelination in a mouse model of Pelizaeus-Merzbacher disease.

Duplication of PLP1, an X-linked gene encoding the major myelin membrane protein of the human CNS, is the most frequent cause of Pelizaeus-Merzbacher disease (PMD). Transgenic mice with extra copies of the wild type Plp1 gene, a valid model of PMD, also develop a dysmyelinating phenotype dependant on gene dosage. In this study we have examined the effect of increasing Plp1 gene dosage on levels of PLP/DM20 and on other representative myelin proteins. In cultured oligodendrocytes and early myelinating oligodendrocytes in vivo, increased gene dosage leads to elevated levels of PLP/DM20 in the cell body. During myelination, small increases in Plp1 gene dosage (mice hemizygous for the transgene) elevate the level of PLP/DM20 in oligodendrocyte soma but cause only minimal and transient effects on the protein composition and structure of myelin suggesting that cells can regulate the incorporation of proteins into myelin. However, larger increases in dosage (mice homozygous for the transgene) are not well tolerated, leading to hypomyelination and alteration in the cellular distribution of PLP/DM20. A disproportionate amount of PLP/DM20 is retained in the cell soma, probably in autophagic vacuoles and lysosomes whereas the level in myelin is reduced. Increased Plp1 gene dosage affects other myelin proteins, particularly MBP, which is transitorily reduced in hemizygous mice but consistently and markedly lower in homozygotes in both myelin and naïve or early myelinating oligodendrocytes. Whether the reduced MBP is implicated in the pathogenesis of dysmyelination is yet to be established.

Animals↗

PubMed2006

Synthesis of a naphthyridone p38 MAP kinase inhibitor.

Compound 1 is a p38 MAP kinase inhibitor potentially useful for the treatment of rheumatoid arthritis and psoriasis. A novel six-step synthesis suitable for large-scale preparation was developed in support of a drug development program at Merck Research Laboratories. The key steps include a tandem Heck-lactamization, N-oxidation, and a highly chemoselective Grignard addition of 4-(N-tert-butylpiperidinyl)magnesium chloride to a naphthyridone N-oxide. The N-oxide exerted complete chemoselectivity via chelation in directing the Grignard addition to the alpha position as opposed to 1,4-addition on the ene-lactam. The dihydropyridyl adduct was in situ aromatized with isobutylchloroformate followed by heating in pyridine. Syntheses of Grignard precursor, N-tert-butyl-4-chloro-piperidine, were accomplished via transamination with a quaternary ammonium piperidone or via addition of methylmagnesium chloride to an iminium ion. Utilizing this chemistry, multi-kilogram preparation of compound 1 was successfully demonstrated.

Cyclic N-Oxides↗

PubMed2006

Efficient access to azaindoles and indoles.

[Structure: see text] An expedient, catalytic method for the synthesis of diverse azaindoles and indoles, starting from readily available and inexpensive starting materials, is described. Conditions were developed for effective reductive alkylation of electron-deficient o-chloroarylamines, substrates previously viewed as poor partners in this reaction. The derived N-alkylated o-chloroarylamines were elaborated to N-alkylazaindoles and N-alkylindoles via a novel one-pot process comprising copper-free Sonogashira alkynylation and a base-mediated indolization reaction.

Alkylation↗

PubMed2006

Efficient access to cyclic ureas via Pd-catalyzed cyclization.

[Structure: see text] An efficient regioselective method for the preparation of structurally diverse imidazopyridinones and benzoimidazolones starting from readily available and economical starting materials is described. High-yielding reductive alkylation of electron-deficient o-haloarylamines followed by treatment with inexpensive N-chlorosulfonyl isocyanate afforded primary ureas in good overall yields. A Pd-catalyzed urea cyclization reaction furnished imidazopyridinones and benzoimidazolones in excellent yields. Overall, the developed chemistry provides rapid access to pharmaceutically important heterocyclic compounds with high efficiency.

Benzimidazoles↗

PubMed2006

Processing of PLP in a model of Pelizaeus-Merzbacher disease/SPG2 due to the rumpshaker mutation.

The rumpshaker mutation of the X-linked myelin proteolipid protein (PLP1) gene causes spastic paraplegia type 2 or a mild form of Pelizaeus-Merzbacher disease in man. The identical mutation occurs spontaneously in mice. Both human and murine diseases are associated with dysmyelination. Using the mouse model, we show that the low steady state levels of PLP result from accelerated proteasomal degradation rather than decreased synthesis. The T(1/2) for degradation of rumpshaker PLP is 11 h compared with 23 h for wild type. A minority of newly synthesized PLP is incorporated into myelin in the correct orientation but at a reduced rate compared with wild type. However, inhibition of proteasomal degradation does not increase the level of PLP incorporated into myelin. As Plp null mice do not have a similar myelin deficiency, it is unlikely that the reduced PLP levels are the main cause of the dysmyelination. Rumpshaker oligodendrocytes also have a reduced level of other myelin proteins, such as MBP, although the mechanisms are not yet defined but are likely to operate at a translational or post-translational level.

Animals↗

PubMed2005

Mild and practical method for the alpha-arylation of nitriles with heteroaryl halides.

[reaction: see text] A mild and transition-metal-free method for the alpha-arylation of aliphatic nitriles with activated heteroaryl halides was developed using NaHMDS or KHMDS as base at ambient temperature. The key to the success of this method is generation of the nitrile anion in the presence of the heteroaryl halide. The method is applicable to both primary and secondary carbonitriles and a wide range of heteroaryl halides. Selective monoarylation was observed with primary carbonitriles. The operational simplicity and the mild reaction conditions add to the value of this method as a practical alternative to the preparation of alpha-heteroaryl carbonitriles.

Alkylation↗

PubMed2005

Suzuki-Miyaura cross-coupling of benzylic phosphates with arylboronic acids.

[reaction: see text] Suzuki-Miyaura cross-coupling of benzylic phosphates with arylboronic acids was investigated. Optimum conditions employed the simple catalytic system of palladium(II) acetate (1 mol %) and triphenylphosphine (4 mol %) with either potassium phosphate or potassium carbonate as the base and toluene as the solvent at 90 degrees C. Using the developed conditions, a series of structurally diverse diarylmethanes were prepared.

Benzene Derivatives↗

PubMed2005

Characterization of the murine splice variant Mobp155: developmental CNS expression pattern and subcellular localization of epitope-tagged protein.

Members of the myelin-associated oligodendrocytic basic protein (MOBP) family constitute the third most abundant protein in CNS myelin. Although MOBP localizes to the major dense line (MDL) of CNS myelin, the function of the individual isoforms is unknown. Alternative splicing of pre-Mobp mRNA gives rise to six characterized splice variants in both the mouse and the rat. These splice variants share a common N-terminal encoded in Mobp exon 3 comprising 68 amino acids. The predicted protein isoforms differ in their C-termini. Sequence analysis of intron 3 revealed the presence of a putative initiation codon followed by an open reading frame (ORF) encoding 53 amino acids that extends in frame into Mobp exon 4 yielding a predicted MOBP isoform comprising 155 amino acids, designated MOBP155. This newly characterized isoform possessing a novel N-terminus shares a common C-terminus with MOBP170. Mobp170 message is detectable at low abundance throughout myelinogenesis. In contrast, the novel splice variant encoding MOBP155 is expressed at modest levels late in CNS development, coincident with the expression of the abundant splice variant, Mobp81A. Immunostaining of Cos7 cells transiently expressing an epitope-tagged MOBP155 suggested that most of the product was translocated to mitochondria. Although Mobp155 and Mobp170 encode a common predicted C-terminus they have different expression profiles and their products are targeted to mitochondria and the nucleus, respectively, in transiently transfected Cos7 cells.

Alternative Splicing↗

PubMed2005

Synthesis of 1-tert-butyl-4-chloropiperidine: generation of an N-tert-butyl group by the reaction of a dimethyliminium salt with methylmagnesium chloride.

Two efficient routes to 1-tert-butyl-4-chloropiperidine are described. In the first route, the key thionyl chloride mediated chlorination reaction features the use of tetrabutylammonium chloride as an additive that effectively suppresses the formation of an elimination-derived side product. In the second route, a novel alternative synthesis of 1-tert-butyl-4-chloropiperidine was developed in which the tertiary butyl group on the nitrogen is efficiently generated through the addition of methylmagnesium chloride to a dimethyliminium salt in 71% overall yield.

Butanes↗

PubMed2004

Oligodendroglial modulation of fast axonal transport in a mouse model of hereditary spastic paraplegia.

Oligodendrocytes are critical for the development of the plasma membrane and cytoskeleton of the axon. In this paper, we show that fast axonal transport is also dependent on the oligodendrocyte. Using a mouse model of hereditary spastic paraplegia type 2 due to a null mutation of the myelin Plp gene, we find a progressive impairment in fast retrograde and anterograde transport. Increased levels of retrograde motor protein subunits are associated with accumulation of membranous organelles distal to nodal complexes. Using cell transplantation, we show categorically that the axonal phenotype is related to the presence of the overlying Plp null myelin. Our data demonstrate a novel role for oligodendrocytes in the local regulation of axonal function and have implications for the axonal loss associated with secondary progressive multiple sclerosis.

Alleles↗

PubMed2003

Multigram synthesis of the C29-C51 subunit and completion of the total synthesis of altohyrtin C (spongistatin 2).

A multigram synthesis of the C29-C51 subunit of altohyrtin C (spongistatin 2) has been accomplished. Union of this intermediate with the C1-C28 fragment and further elaboration furnished the natural product. Completion of the C29-C51 subunit began with the aldol coupling of the boron enolate derived from methyl ketone 8 and aldehyde 9. Acid-catalyzed deprotection/cyclization of the resulting diastereomeric mixture of addition products was conducted in a single operation to afford the E-ring of altohyrtin C. The diastereomer obtained through cyclization of the unwanted aldol product was subjected to an oxidation/reduction sequence to rectify the C35 stereocenter. The C45-C48 segment of the eventual triene side chain was introduced by addition of a functionalized Grignard reagent derived from (R)-glycidol to a C44 aldehyde. Palladium-mediated deoxygenation of the resulting allylic alcohol was followed by adjustment of protecting groups to provide reactivity suitable for the later stages of the synthesis. The diene functionality comprising the remainder of the C44-C51 side chain was constructed by addition of an allylzinc reagent to the unmasked C48 aldehyde and subsequent dehydration of the resulting alcohol. Completion of the synthesis of the C29-C51 subunit was achieved through conversion of the protected C29 alcohol into a primary iodide. The synthesis of the C29-C51 iodide required 44 steps with a longest linear sequence of 33 steps. From commercially available tri-O-acetyl-d-glucal, the overall yield was 6.8%, and 2 g of the iodide was prepared. The C29-C51 primary iodide was amenable to phosphonium salt formation, and the ensuing Wittig coupling with a C1-C28 intermediate provided a fully functionalized, protected seco-acid. Selective deprotection of the required silicon groups afforded an intermediate appropriate for macrolactonization, and, finally, global deprotection furnished altohyrtin C (spongistatin 2). This synthetic approach required 113 steps with a longest linear sequence of 37 steps starting from either tri-O-acetyl-d-glucal or (S)-malic acid.

Aldehydes↗

PubMed2003

An efficient procedure for the preparation of 4-substituted 5-aminoimidazoles.

The preparation of O-methylimidates from alpha-aminonitriles and their subsequent co-cyclization with primary amines to afford 4-substituted 5-aminoimidazoles was studied. It was found that the mildly acidic pyridinium p-toluenesulfonate efficiently catalyzed each stage of the reaction sequence: (a) the formation of the O-methylimidates, (b) their co-cyclization with a variety of primary amines, and (c) certain derivatizations of the resultant heterocycles. The developed reaction conditions tolerate a wide variety of alpha-aminonitriles and primary amine co-reactants. Thus, it is possible to easily prepare a diverse array of substituted heterocyclic compounds in good yield. The requisite alpha-aminonitriles were synthesized either from amino acids or by phase-transfer alkylation of a glycine anion equivalent. The unstable free 5-aminoimidazoles were normally protected in situ to provide derivatives (methyl imidates or N,N-dimethylamidines) that were amenable to characterization.

Journal Article↗