Abstract: The present invention is directed to compounds of the formula I: Wherein R1, R2, R3, R4, R5, R6, R7, R8, R9, X, n and the broken lines are as defined herein which are useful as modulators of chemokine receptor activity. In particular, these compounds are useful as modulators of the chemokine receptor CCR-2.

Abstract: An aminomethylpyridyloxymethyl/benzisoxazole substituted azabicyclic compound of formula I, pharmaceutical composition comprising same, and a method of treating one or more CNS or other disorders, including concurrent treatment of disorders such as schizophrenia and depression, wherein formula I is or a pharmaceutically acceptable salt or thereof, wherein Z is wherein Y is methylene; X is oxygen; n is 0; R1 and R2 are each hydrogen or halogen; and R3 and R4 together with the nitrogen atom to which they are attached form i) a saturated non-aromatic 3 to 7 membered monocyclic ring, said ring i) being unsubstituted or substituted or substituted with one or more (C1–C4)alkyl, (C1–C4)alkoxy(C1–C4)alkyl, or hydroxy groups.

Abstract: Disclosed are compounds of formula (I) Where Ar1, X, Y, Q, W, R3, R4, R5, R6 and Ry are defined herein. The compounds of the invention inhibit production of cytokines involved in inflammatory processes and are thus useful for treating diseases and pathological conditions involving inflammation such as chronic inflammatory disease. The compounds are also useful for treating diseases or conditions related to oncology and anticoagulant or fibrinolytic therapy. Also disclosed are processes for preparing these compounds and pharmaceutical compositions comprising these compounds.

Abstract: The present invention relates to 1-[(indol-3-yl)carbonyl]piperazine derivative according to the general formula I or a pharmaceutically acceptable salt thereof. The invention also relates to pharmaceutical compositions comprising said 1-[(indol-3-yl)carbonyl]piperazine derivatives, and to the use of these derivatives in the treatment of pain, such as peri-operative pain, chronic pain neuropathic pain, cancer pain, and pain and spasticity associated with multiple sclerosis.

Abstract: This invention relates to novel diazabicyclic biaryl derivatives, which are found to be cholinergic ligands at the nicotinic acetylcholine receptors and modulators of the monoamine receptors and transporters. Due to their pharmacological profile the compounds of the invention may be useful for the treatment of diseases or disorders as diverse as those related to the cholinergic system of the central nervous system (CNS), the peripheral nervous system (PNS), diseases or disorders related to smooth muscle contraction, endocrine diseases or disorders, diseases or disorders related to neuro-degeneration, diseases or disorders related to inflammation, pain, and withdrawal symptoms caused by the termination of abuse of chemical substances.

Abstract: This invention relates to a method for treating an angiogenesis-related disease. The method includes administering to a subject in need thereof an effective amount of a piperazinedione compound having the formula: In the above formula, each of and , independently, is a single bond or a double bond; A is H or CH(RaRb) when is a single bond, or C(RaRb) when is a double bond; Z is CH(RcRd) when is a single bond, or C(RcRd) when is a double bond; each of R1 and R2, independently, is H, C(O)Re, C(O)ORe, C(O)NReRf, or SO2Re; and each of Ra, Rb, Rc, Rd, Re, and Rf, independently, is H, C1-C6 alkyl, aryl, heteroaryl, C3-C8 cycloalkyl, or C3-C8 heterocycloalkyl; or Ra and Rb taken together are C3-C8 cycloalkyl, C3-C8 heterocycloalkyl, aryl, or heteroaryl; or R1 and Ra or R1 and Rb taken together are C3-C8 cycloalkyl, C3-C8 heterocycloalkyl, aryl, or heteroaryl; provided that one of Rc and Rd is aryl or heteroaryl.

Abstract: Described herein are compounds with affinity for the 5-HT6 receptor, which have the general formula I: Wherein A, B, D, E, R1 to R3 and n are described herein. Also described is the use of these compounds as pharmaceuticals to treat indications where inhibition of the 5-HT6 receptor is implicated, such as schizophrenia.

Abstract: The present invention is directed to small molecule inhibitors of the IgE response to allergens, which are useful in the treatment of allergy and/or asthma or any diseases where IgE is pathogenic. This invention also relates to phenyl-aza-benzimidazole molecules that are cellular proliferation inhibitors and thus are useful as anticancer agents. This invention further relates to small molecules which suppress cytokines and leukocytes.

Abstract: Compounds of Formula I are provided, in which variables are as described herein: Such compounds may be used to modulate MCH binding to MCH receptors in vivo or in vitro, and are particularly useful in the treatment of a variety of metabolic, feeding and sexual disorders in humans, domesticated companion animals and livestock animals. Pharmaceutical compositions and methods for treating such disorders are provided, as are methods for using such ligands for detecting MCH receptors (e.g., receptor localization studies).

Abstract: The invention relates to hexahydro-pyrido[1,2-a]pyrazine derivatives having interesting neurokinin-NK1 receptor antagonistic activity. The invention also relates to methods for the preparation of these compounds, to pharmaceutical compositions containing a pharmacologically active amount of at least one of these compounds as an active ingredient, as well as to the use of these compositions for the treatment of disorders in which neurokinin receptors are involved. The invention relates to compounds represented by the general formula (1) wherein the symbols have the meanings as given in the description.

Abstract: This invention relates to novel diazabicyclic biaryl derivatives, which are found to be cholinergic ligands at the nicotinic acetylcholine receptors and modulators of the monoamine receptors and transporters. Due to their pharmacological profile the compounds of the invention may be useful for the treatment of diseases or disorders as diverse as those related to the cholinergic system of the central nervous system (CNS), the peripheral nervous system (PNS), diseases or disorders related to smooth muscle contraction, endocrine diseases or disorders, diseases or disorders related to neuro-degeneration, diseases or disorders related to inflammation, pain, and withdrawal symptoms caused by the termination of abuse of chemical substances.

Abstract: This invention relates to novel 1,4-diazabicycloalkane derivatives and their use in the manufacture of pharmaceutical compositions. The compounds of the invention are found to be cholinergic ligands at the nicotinic acetylcholine receptors and modulators of the monoamine receptors and transporters. Due to their pharmacological profile the compounds of the invention may be useful for the treatment of diseases or disorders as diverse as those related to the cholinergic system of the central nervous system (CNS), the peripheral nervous system (PNS), diseases or disorders related to smooth muscle contraction, endocrine diseases or disorders, diseases or disorders related to neuro-degeneration, diseases or disorders related to inflammation, pain, and withdrawal symptoms caused by the termination of abuse of chemical substances.

Abstract: The present invention relates to a nitrogen-containing fused ring compound represented by the following formula [I] wherein each symbol is as defined in the specification, or a pharmaceutically acceptable salt thereof, and an anti-HIV agent containing such compound. The compound of the present invention has an HIV integrase inhibitory activity, and is useful as an agent for the prophylaxis or treatment of AIDS, or as an anti-HIV agent. In addition, by the combined use with other anti-HIV agents such as a protease inhibitor, a reverse transcriptase inhibitor and the like, it can be a more effective anti-HIV agent. Because it shows integrase-specific high inhibitory activity, the compound can be a pharmaceutical agent safe on human body, which causes only a fewer side effects.

Abstract: The present invention relates to a group of unique diazabicyclo alkane derivatives having interesting neurokinin-NK1 receptor antagonistic activity represented by the general formula (1) wherein: R1 represents phenyl, 2-indolyl, 3-indolyl, 3-indazolyl or benzo[b]thiophen-3-yl, which groups may be substituted with halogen or alkyl (1–3C), R2 and R3 independently represent halogen, H, OCH3, CH3 and CF3, R4, R5 and R6 independently represent H, OH, O-alkyl(1–4C), CH2OH, NH2, dialkyl(1–3C)N, pyrrolidin-1-yl, piperidin-1-yl, morpholin-4-yl or morpholin-4-yl substituted with one or two methyl or methoxymethyl groups, morpholin-4-ylamino, morpholin-4-ylmethyl, imidazol-1-yl, thiomorpholin-4-yl, 1,1-dioxothiomorpholin-4-yl or 3-oxa-8-azabicyclo[3.2.

Abstract: The present invention relates to piperidine derivatives of formula (I): R represents halogen or C1-4 alkyl R1 represents C1-4 alkyl; R2 or R3 independently represent hydrogen or C1-4 alkyl; R4 represents trifluoromethyl, C1-4 alkyl, C1-4 alkoxy, trifluoromethoxy or halogen; R5 represents hydrogen, C1-4 alkyl or C3-7 cycloalkyl; R6 is hydrogen and R7 is a radical of formula (W): ?or R6 is a radical of formula (W) and R7 is hydrogen; X represents CH2, NR5 or O; Y represents Nitrogen and Z is CH or Y represents CH and Z is Nitrogen; A represents C(O) or S(O)q, provided that when Y is nitrogen and Z is CH, A is not S(O)q; m is zero or an integer from 1 to 3; n is an integer from 1 to 3; p and q are independently an integer from 1 to 2; and pharmaceutically acceptable salts and solvates thereof. The process for their preparation and their use in the treatment of a condition mediated by tachykinins.

Abstract: Novel substituted hexahydropyrrolo[1,2-a]pyrazines, octahydropyrido[1,2-a]-pyrazines and decahydropyrazino[1,2-a]azepines, use of these compounds as pharmaceutical compositions, pharmaceutical compositions comprising the compounds, and a method of treatment employing these compounds and compositions. The compounds show a high and selective binding affinity to the histamine H3 receptor indicating histamine H3 receptor antagonistic, inverse agonistic or agonistic activity. As a result, the compounds are useful for the treatment of diseases and disorders related to the histamine H3 receptor.

Abstract: Heterocyclic compounds that bind chemokine receptors and inhibit the binding of their natural ligands are disclosed. The invention compounds are protective against infection by HIV and exert effects characteristic of antagonists to the CXCR4 receptor.

Abstract: The present invention relates to new derivatives of sulphonamides, with the general formula (I), as well as to their physiologically acceptable salts, the processes for their preparation, their application as medicaments in human and/or veterinary therapy and the pharmaceutical compositions that contain them

Abstract: Specified phenylalanine derivatives and analogues thereof have an antagonistic activity to ?4 integrin. They are used as therapeutic agents for various diseases concerning ?4 integrin.

Abstract: The present invention is to provide an aliphatic nitrogen-containing 5-membered ring compound represented by the formula [I]: wherein A represents —CH2— or —S—, R1 represents hydrogen atom, a lower alkyl group, a hydroxy lower alkyl group or a lower-alkoxy lower alkyl group, X represents —N(R3)—, —O— or —CO—, where R3 represents hydrogen atom or a lower alkyl group, and R2 represents (1) a cyclic group which may be substituted, or (2) an amino group which may be substituted, or a pharmaceutically acceptable salt thereof, a method for preparing the above-mentioned compound and a pharmaceutical composition comprising the above-mentioned compound as an effective ingredient.

Abstract: The present invention concerns compounds of general formula (I): in which the substituents are as described herein.

Abstract: The present invention relates to a compound of the general formula (I): [Ar1 is aryl fused to the adjacent pyrazinone ring at the 5th and 6th positions, etc., X is CO, etc., Y is CH, etc., Z is CH, etc., V is CH, etc., Wn is —(CH2)n— (n is zero to four), R1, is H or optionally substituted lower alkyl, etc., R2 is H, etc., R3 and R4 are the same or different and are each H, etc., R5 and R6 are the same or different and are each H, hydroxy, etc.] or a pharmaceutically acceptable salt or ester thereof; a pharmaceutical composition, an inhibitor of Cdk4 and/or Cdk6 or an anti-cancer agent, containing the same as an active ingredient; and a process for preparing them.

Abstract: The present invention relates to substituted sulfonamide compounds of the general formula (I), wherein P is sulfonamide or amide-substituted sulfonic acid, which compounds are potentially useful for the prophylaxis and treatment of medical conditions relating to obesity, type II diabetes and/or disorders of the central nervous system

Abstract: Compounds according to formula (1), wherein R1 is H or CN, X1 is S, O, SO2 or CH2, X2 is CO, CH2 or a covalent bond, Het is a nitrogen-containing heterocycle and n is 1–5 are new. The compounds of the invention are inhibitors of dipeptidyl peptidase IV.

Abstract: This invention provides compounds which are represented by a general formula [I] [in which X stands for hydrogen or halogen; B stands for halogen, cyano or optionally fluorine-substituted lower alkyl; D stands for a 3–10 membered aliphatic nitrogen-containing heterocyclic group; R3, R4 and R5 may be same or different, and each stands for hydrogen, lower alkyl optionally having substituent group(s) and the like; and a is 0 or 1]. These compounds exhibit high affinity to nociceptin receptors and whereby inhibit actions of nociceptin, and are useful as an analgesic, antiobestic, agent for ameliorating brain function, treating agents for Alzheimer's disease and dementia, and therapeutic agents for schizophrenia, neurodegenerative diseases, depression, diabetes insipidus, polyuria, hypotension and the like.

Abstract: The invention provides compounds of Formula I and derivatives thereof, pharmaceutical compositions comprising a compound of Formula I, and methods of treatment utilizing such compounds and compositions: wherein: R1 is chosen from optionally substituted aryl, optionally substituted aralkyl, optionally substituted heteroaryl, and optionally substituted heteroaralkyl; L is a linker; R2 is chosen from optionally substituted aryl, optionally substituted aralkyl, optionally substituted heteroaryl, and optionally substituted heteroaralkyl; and or single stereoisomers, mixtures of stereoisomers, or the pharmaceutically acceptable salts, amides, or esters thereof.

Abstract: This invention is directed to a compound of the formula I as defined herein, or a pharmaceutically acceptable salt thereof; a pharmaceutical composition containing a compound of formula I, a method of treatment of a disorder or condition that may be treated by modulating histamine H3 receptors, the method comprising administering to a mammal in need of such treatment a compound of formula I as described above, and a method of treatment of a disorder or condition selected from the group consisting of depression, mood disorders, schizophrenia, anxiety disorders, Alzheimer's disease, attention-deficit hyperactivity disorder (ADHD), psychotic disorders, sleep disorders, obesity, dizziness, epilepsy, motion sickness, respiratory diseases, allergy, allergy-induced airway responses, allergic rhinitis, nasal congestion, allergic congestion, congestion, hypotension, cardiovascular disease, diseases of the GI tract, hyper and hypo motility and acidic secretion of the gastro-intestinal tract, the method comprising a

Abstract: The invention provides 2, 3-, 4- or 5-substituted-N1-(arylsulfonyl)indole and (heteroaryl)indole compounds of the general formula (I): in which Ar, R2, R3, R4 and R5 are as defined in the specification. The compounds bind to the 5-HT6 receptor and are useful for the treatment and prophylaxis of disorders mediated by the 5-HT6 receptor, such as obesity and CNS disorders.

Abstract: The present invention relates to polymeric charge transport compositions. The invention further relates to electronic devices in which there is at least one active layer comprising such charge transport compositions.

Abstract: The invention relates to compounds of the general formula (I): wherein Ar is optionally substituted aryl or heteroaryl; A is (i) —O—, —S—, —SO2—, —NH—, (ii) a C1-4-alkyl- or C1-6-acyl-substituted nitrogen atom or (iii) a C1-8-alkylene chain or a heteroalkylene chain having 2 to 8 chain atoms, which optionally contains at least one unsaturation, and which may be substituted and/or contain a bridge to form a saturated or partially or fully unsaturated ring having 3-8 ring members; B is —C(R4)(R5)—, —OC(R4)(R5)—, —N(R6)C(R4)(R5)—, —N(R6)—, —O—, —S— or —SO2—; R is optionally substituted C3-8-cycloalkyl, aryl or heteroaryl; R1 is (i) a saturated or unsaturated azacyclic or aminoazacyclic ring, or a saturated diazacyclic or aminodiazacyclic ring, which has 4 to 7 ring members, or a saturated aminoazabicyclic, azabicyclic or diazabicyclic ring which has 7 to 10 ring members, which rings optionally are substituted in one or more positions, or a group —[C(R4)(R5)]xN(R2a)(R3a)]; R2a, R3a, R4, R5, R6 and x are as

Abstract: A compound of the formula wherein D, E, F, G, L, T, W, X, Y, Z, U, A, R1, R2, R3, R4, R5, R6 R7 are as defined in the specification, pharmaceutical compositions thereof, and methods of use to treat diseases and as D3 receptor modulators.

Abstract: The present invention relates generally to compounds that inhibit serine proteases. In particular it is directed to novel amino-bicyclic pyrazinone and pyridinone compounds of Formula (I): or a stereoisomer or pharmaceutically acceptable salt form thereof, which are useful as selective inhibitors of serine protease enzymes of the coagulation cascade; for example thrombin, factor Xa, factor XIa, factor IXa, and/or factor VIIa. In particular, it relates to compounds that are factor VIIa inhibitors. This invention also relates to pharmaceutical compositions comprising these compounds and methods of using the same.

Abstract: A compound represented by the general formula: wherein R20 is —CH2COOH and the like; R21 is —COCONH2 and the like; R22 is C4–C6 alkyl; and the like; R23 is —CH2—R18 wherein R18 is aryl and the like; R24 is hydrogen or C1–C6 alkyl and the like; an optical active compound, a prodrug thereof, or a pharmaceutically acceptable salt, or a solvate having type X sPLA2 inhibitory effect was found.

Abstract: A compound selected from those of formula (I): wherein: Ra represents linear or branched (C1–C6)alkylene, X represents a group selected from W1, —C(W1)—W2—, —W2—C(W1)—, —W2—C(W1)W2—, —W2—Ra— and —CH(OR1)— wherein W1, W2 and R1 are as defined in the description, when Y represents aryl or heteroaryl, or X represents a group selected from single bond, —C(W1)—, —W2—C(W1)—, —W2—Ra and —CH(OR1)— wherein W1, W2, Ra and R1 are as defined hereinbefore, when Y represents a fused bicyclic group, of formula: wherein: A represents nitrogen-containing heterocycle having from 4 to 7 ring members that is unsaturated or partially saturated and optionally contains a second hetero atom, B represents phenyl ring optionally substituted by one or more groups as defined in the description, its isomers, and addition salts thereof with a pharmaceutically acceptable acid or base, medicinal products containing the same are useful in the treatment of cognitive deficiencies.

Abstract: The invention provides piperidine and piperazine derivatives of general formula (I), processes for their preparation, pharmaceutical compositions containing them, a process for preparing the pharmaceutical compositions, and their use in therapy

Abstract: The object of the present invention is to provide soluble ?-amyloid precursor protein secretory stimulators, which are effective in treating neurodegenerative diseases as well as cerebrovascular disorder-induced neuronopathy. More specifically, the present invention provides a novel compound of the following Formula (I) or a salt or prodrug thereof: [wherein R1 and R2 each represent a hydrogen atom or a lower alkyl group, etc., Ar1 and the ring B each represent an optionally substituted aromatic group, the ring A represents an optionally substituted benzene ring, the ring C represents an optionally substituted 4- to 8-membered ring which may further be condensed with an optionally substituted ring, X represents CH or N, and Y represents CH or N].

Abstract: Novel non-peptide GLP-1 agonists, pharmaceutical compositions comprising them, use of the non-peptide GLP-1 agonists for the preparation of pharmaceutical compositions and methods for the treatment and/or prevention of disorders and diseases wherein an activation of the human GLP-1 receptor is beneficial, especially metabolic disorders such as IGT, Type 1 diabetes, Type 2 diabetes and obesity.

Abstract: Aza- and polyaza-naphthalenyl carboxamide derivatives including certain quinoline carboxamide and naphthyridine carboxamide derivatives are described. These compounds are inhibitors of HIV integrase and inhibitors of HIV replication, and are useful in the prevention or treatment of infection by HIV and the treatment of AIDS, as compounds or pharmaceutically acceptable salts, or as ingredients in pharmaceutical compositions, optionally in combination with other antivirals, immunomodulators, antibiotics or vaccines. Methods of preventing, treating or delaying the onset of AIDS and methods of preventing or treating infection by HIV are also described.

Abstract: Novel substituted hexahydropyrrolo[1,2-a]pyrazines, octahydropyrido[1,2-a]-pyrazines and decahydropyrazino[1,2-a]azepines, use of these compounds as pharmaceutical compositions, pharmaceutical compositions comprising the compounds, and a method of treatment employing these compounds and compositions. The compounds show a high and selective binding affinity to the histamine H3 receptor indicating histamine H3 receptor antagonistic, inverse agonistic or agonistic activity. As a result, the compounds are useful for the treatment of diseases and disorders related to the histamine H3 receptor.

Abstract: Novel 6-bicyclopiperazinyl-1-arylsulfonylindole and 6-bicyclopiperidinyl-1-arylsulfonylindole compounds are disclosed which are useful as 5-HT6 receptor antagonists in the treatment of central nervous system disorders such as schizophrenia, depression, ADHD, and cognition and memory dysfunction The compounds are Formula I wherein: R1 is H or C1-4 alkyl; X is CH, —C—OR3, ?C, or —N and Y is C-R2 or N; R3 is H or —C(O)-R4; R4 is H or a labile prodrug group; n is 1 or 2; m and o are, independently, 0, 1, or 2 with the proviso that m+o is 1 or 2; and Ar is an aryl or heteroaryl group optionally substituted with 1-3 substitutents.

Abstract: Compounds of formula wherein the substituents have the meanings given in claim 1, and agronomically tolerable salts, isomers and enantiomer of those compounds, are suitable for use as herbicides.

Abstract: Heterocyclic are provided which are sodium/proton exchange (NHE) inhibitors which have the structure wherein n is 1 to 5; X is N or C—R5 wherein R5 is H, halo, alkenyl, alkynyl, alkoxy, alkyl, aryl or heteroaryl; Z is a heteroaryl gorup, R1, R2, R3 and R4 are as defined herein, and where X is N. R1 is preferably aryl or heteroaryl, and are useful as antianginal and cardioprotective agents. In addition, a method is provided for preventing or treating angina pectoris, cardiac dysfunction, myocardial necrosis, and arrhythmia employing the above heterocyclic derivatives.

Abstract: The invention provides compounds of Formula I: These compounds may be in the form of pharmaceutical salts or compositions, may be in pure enantiomeric form or racemic mixtures, and are useful in pharmaceuticals to treat conditions or diseases in which ?7 is known to be involved.

Abstract: Compounds which are useful as potassium channel inhibitors and which because of their slow off-rates are especially useful for the treatment of cardiac arrhythmias are described.

Abstract: Compounds as potassium channel inhibitors and especially useful for the treatment of cardiac arrhythmias and cell proliferative disorders are described.

Abstract: Specified phenylalanine derivatives and analogues thereof have an antagonistic activity to ? 4 integrin. They are used as therapeutic agents for various diseases concerning ? 4 integrin.

Abstract: This invention is directed to quinoline/quinoxaline compounds which inhibit platelet-derived growth factor or p56lck tyrosine kinase activity, to pharmaceutical compositions comprising these compounds, and to the use of these compounds for treating a patient suffering from or subject to disorders/conditions involving cellular differentiation, proliferation, extracellular matrix production or mediator release and/or T cell activation and proliferation.

Abstract: The present invention relates to diazabicyclic compounds, preferably to N-aryl diazabicyclic compounds. Of particular interest are 2-pyridinyl diazabicyclic compounds, such as (1S,4S)-2-(5-(3-methoxyphenoxy)-3-pyridyl)-2,5-diazabicyclo[2.2.1]heptane. Other exemplary compounds of the present invention include (1S,4S)-2-(5-(4-methoxyphenoxy)-3-pyridyl)-2,5-diazabicyclo[2.2.1]heptane, (1S,4S)-2-(5-(3-thienyl)-3-pyridyl)-2,5-diazabicyclo[2.2.1]heptane, (1S,4S)-2-(5-(4-fluorophenoxy)-3-pyridyl)-2,5-diazabicyclo[2.2.1]heptane, and (1S,4S)-2-(5-benzoyl-3-pyridyl)-2,5-diazabicyclo[2.2.1]heptane. The present invention also relates to prodrug derivatives of the compounds of the present invention.

Abstract: Compounds useful as potassium channel inhibitors and especially useful for the treatment of cardiac arrhythmias and cell proliferative disorders are described.

Abstract: The present invention is to provide an aliphatic nitrogen-containing 5-membered ring compound represented by the formula [I]: wherein A represents —CH2— or —S—, R1 represents hydrogen atom, a lower alkyl group, a hydroxy lower alkyl group or a lower alkoxy lower alkyl group, X represents —N(R3)—, —O— or —CO—, where R3 represents hydrogen atom or a lower alkyl group, and R2 represents (1) a cyclic group which may be substituted, or (2) an amino group which may be substituted, or a pharmaceutically acceptable salt thereof, a method for preparing the above-mentioned compound and a pharmaceutical composition comprising the above-mentioned compound as an effective ingredient.

Abstract: A digitally trunked radio repeater system provides substantial improvements in timeliness of channel acquisition and channel drop, and in reliability of critical control signalling. The system uses a much higher digital signalling rate than is typically found in prior art systems, and uses a control channel to convey digital channel request and assignment messages between the central site and mobile transceivers. The mobile radio transceivers transmit channel requests on the control channel (if no response is received, the mobile retries during a retry time window which increases in duration in dependence on the number of retries). The mobile transceiver switches to a working channel in response to an assignement message received on the control channel. Subaudible digital signals transmitted on the control channel and on active working channels allow late entry, shifting to higher priority calls, and other advanced functions.