Synthesis and anti-HBV activity of carbocyclic nucleoside hybrids with salient features of entecavir and aristeromycin.

Modified carbocyclic nucleosides (4a-g) constituting 7-deazapurine, 4'-methyl, exocyclic double bond and 2',3'-hydroxy were synthesized. NOE and X-ray studies of 4c confirmed the α-configuration of 4'-methyl. The anti-HBV assay demonstrated 4e (IC50 = 3.4 µM) without notable cytotoxicity (CC50 = 87.5 µM) as a promising lead for future exploration.

Rhodium catalyzed stereospecific reductive carbocyclization of 1,6-enynes and synthesis of 4'-methyl-6'-substituted aristeromycins.

The need of long-term treatment for chronic HBV, emergence of drug-resistant viruses and inefficiency of currently approved therapies to eliminate covalently closed circular DNA (cccDNA), mandates identification of potent and selective inhibitors of HBV replication with novel mechanisms of action. Entecavir, a carbocyclic guanosine nucleoside analog, is the most potent inhibitor of HBV replication on the market. Moreover, the naturally occurring carbocyclic nucleosides aristeromycin are known for their wide range of antiviral activities. In this research, we have utilized BINAP directed rhodium catalyzed reductive carbocyclization of 1,6-enynes (8a-b) through asymmetric hydrogenation which is an approach, not yet explored in carbocyclic sugar synthesis. Interestingly, we obtained exclusive anti-(9a) and Z-anti (9b) carbocyclic sugars. The new aristeromycin analogs (10a-b) with scaffold combination of entecavir and aristeromycin were then synthesized using the Mitsunobu reaction followed by deprotection.

Synthesis and anti-HBV activity of α-stereoisomer of aristeromycin based analogs.

The potential antiviral activity of aristeromycin type of derivatives (I) is limited by associated toxicity due to its possible 5'-O-phosphorylation and S-adenosyl-l-homocysteine hydrolase (SAHase) inhibitory activity. Aristeromycin structure has major pharmacophoric motif as 5'-OH and adenosine base, which may have significant role in enzyme binding followed by activity and or toxicity. Thus, the structural optimization to alter this major motif by replacing with its bioisostere and changing the 5'-O conformation through stereochemistry reversal was of interest. Thus, the inverted stereochemistry at 4'-position coupled with bioisostere of adenosine base in the target compounds (6-7) to access antiviral potential. The stereoselective formation of a key stereoisomer (2a) was achieved exclusively from neplanocin sugar (1a) by reduction in a single step. The novel target molecules (6-7) were synthesized in 4 steps with 55-62% yield. Compound 6 was analyzed by single crystal X-ray diffraction, which confirms the stereoselective formation of α-analogs with highly puckered cyclopentane ring and 2'-endo conformation. The compound 6 shown significant anti-hepatitis B virus activity of 6.5µM with CC50>100µM and yielded a promising lead with novel structural feature.

Regioselective Synthesis of Pyrazolo[3,4-D]Pyrimidine Based Carbocyclic Nucleosides as Possible Antiviral Agent.

Carbocyclic nucleosides are considered as nucleoside mimetic having high therapeutic potentials, however diverse exploration is still limited due to their synthetic difficulties. The major challenges are associated with the preparation of new base and carbocyclic sugar key intermediates. The modified base may provide conformational advantage to achieve better nucleoside mimetics and may also help in increasing the drug-like properties. In this manuscript, we report the use of acetamidine hydrochloride to synthesize 6-methyl-4-amino-pyrazolo[3,4-d]pyrimidine base and regioselective synthesis of six new carbocyclic nucleosides (6a-f) for antiviral evaluation. Theoretical investigations were carried out on the basis of thermodynamic and kinetic stability using MM based energy optimizations and QM based transition state search for the significant regioselectivity, which was further experimentally analyzed by NOE and UV spectroscopy.

NAD+-dependent DNA ligase (Rv3014c) from Mycobacterium tuberculosis: novel structure-function relationship and identification of a specific inhibitor.

Mycobacterium tuberculosis codes for an essential NAD+-dependent DNA ligase (MtuLigA) which is a novel, validated, and attractive drug target. We created mutants of the enzyme by systematically deleting domains from the C-terminal end of the enzyme to probe for their functional roles in the DNA nick joining reaction. Deletion of just the BRCT domain from MtuLigA resulted in total loss of activity in in vitro assays. However, the mutant could form an AMP-ligase intermediate that suggests that the defects caused by deletion of the BRCT domain occur primarily at steps after enzyme adenylation. Furthermore, genetic complementation experiments using a LigA deficient E. coli strain demonstrates that the BRCT domain of MtuLigA is necessary for bacterial survival in contrast to E. coli and T. filiformis LigA, respectively. We also report the identification, through virtual screening, of a novel N-substituted tetracyclic indole that competes with NAD+ and inhibits the enzyme with IC50 in the low muM range. It exhibits approximately 15-fold better affinity for MtuLigA compared to human DNA ligase I. In vivo assays using LigA deficient S. typhimurium and E. coli strains suggest that the observed antibacterial activity of the inhibitor arises from specific inhibition of LigA over ATP ligases in the bacteria. In silico ligand-docking studies suggest that the exquisite specificity of the inhibitor arises on account of its mimicking the interactions of NAD+ with MtuLigA. An analysis of conserved water in the binding site of the enzyme suggests strategies for synthesis of improved inhibitors with better specificity and potency.

Bacteriological profile in chronic suppurative otitis media in Eastern Nepal.

Aural swabs were collected from 250 patients with chronic suppurative otitis media (CSOM) (tubotympanic disease). Duration of ear discharge was more than 6 months for culture and sensitivity test. The disease was unilateral in 178 (71.2%) and bilateral in 72 (28.8%) patients. From a total of 322 aural swab cultures, 324 organisms were isolated with predominance of Pseudomonas aerugimosa (36.4%) followed by Staphylococcus aureus (30.2%). All the isolated Gram-negative organisms showed in vitro sensitivity to ciprofloxacin, amikacin, ofloxacin, and gentamycin whereas cloxacillin, ofloxacin, erythromycin, ciprofloxacin, gentamicin and tetracycline were more effective against Gram-positive isolates. Most isolates were resistant to amoxycillin. It is concluded that ciprofloxacin is preferred to aminoglycosides as an important tool in the treatment of CSOM because of its lower cost, lack of ototoxicity and availability as topical oral preparations.

Community oriented research program for prevention of deafness with special stress on children - A preliminary report.

A study of community- oriented multilaleral study was carried out in rural community of eastern Nepal where in total of 2564 patients were screened out and it revealed that multi nutritional deficiency comprised of 20% along with unsatisfactory or incomplete immunization was recorded in 45%. Children up-to 14 years of age (1223) were considered for this study. 5-14 years of age were the must vulnerable for ear diseases (50.16%). 61% children were living in over crowded dwellings. The hearing analysis established that the number of conductive deafness were prevalent in 62.46% in comparison to sensory-neural hearing loss 2.40% and mixed hearing loss (0.18%). Due to better ear care, Otorrhoea was under control in 67% cases and so was the conductive deafness improved.

Inverted papilloma of nose with orbital involvement and malignant transformation.

We report two cases of inverted papilloma of nose with malignant transformation and orbital involvement in 60 year and 73 year male patients from Nepal. Medial maxillectomy and orbital exenteration were done in both cases. Histo- pathological examination showed areas of squamous cell carcinoma in inverted papilloma in both of the cases.The dilemma of diagnosis and treatment is discussed with review of literature.

Aneurysmal bone cyst of paranasal sinuses.

Aneurysmal hone cyst is rare in paranasal sinuses. It may be uni or multilocutar It occurs alone or with other benign bone lesions. The exact pathogenesis of it is still unknown. The aggressiveness of the disease needs early diagnosis and proper management to prevent recurrence. This report describes a case of aneurysmal bone cyst involving the ethmoid and maxillary sinuses which was successfully managed.

Nasal cerebral heterotopia: a case report.

Nasal cerebral heterotopia (nasal glioma) are rare congenital benign masses of neurogenic origin with intranasal location, or both. An extranasal case is reported in a 2-year-old-boy without any bony defect or connection with brain. Histology and immunohistochemistry confirmed the diagnosis.