Human immunodeficiency virus (HIV) is one of the most austere and deadly infectious viruses with disastrous concerns ^{1, 2}. Infections with HIV caused Acquired Immune Deficiency Syndrome (AIDS) and it has been considered as a pandemic disease ^{1, 3}. HIV-1 is more common and high infectious than HIV-2. HIV-1 has the ability to mutate and change their genetic makeup over the time like many other viruses. There are many genetically distinct subgroups derived from the main type of HIV. HIV-1 is predominant type of HIV and 95% of total HIV infectious person infected with HIV-1. HIV-1 and HIV-2 viruses are genetically different from each other by almost 55% ⁴. HIV-1 has four subtypes placed in different groups such as M, N, O and P. Group M is the most dominant and infectious in nature and this group have several strains such as A,B, C, D, F, G, H, J, K and Circulating Recombinant Forms (CRFs). CRFs are hybrid viruses formed as a result of combination of the genetic materials of two subtypes ^{5, 6}. HIV has infected to about 70 million people all over the world since the beginning of the epidemic and has caused mortality to about 50% of the infected population. Till the end of 2017, about 37 million people were reported to harbour HIV-1 infection ⁷. About 40 million peoples are suffering from HIV infection and Africa region is a serious victim with 25 million peoples. Every year about 2.4 million deaths occurred due to HIV and AIDS ⁴. According to the National Aids Control Organisation (NACO, India) 2015 reports, in adults HIV occurrence in India was about 0.26% (0.22%–0.32%). HIV prevalence was about 0.30% in males and 0.22% in females in India. Among the Indian states, Manipur has shown the highest estimated adult HIV prevalence of 1.15% and some states have HIV prevalence below 0.20% ⁸.

Reverse transcriptase (RT) is most important enzyme for the retroviruses to complete their life cycle ⁹. Reverse transcriptase (HIV-1 RT) contains 1000 amino acids and is an asymmetric heterodimer. The larger subunit known as p66 contains 560 amino acid long and performing all the enzymatic activities of the RT ¹⁰. Two active sites namely polymerase and ribonuclease H have been found on larger subunit (p66). The smaller subunit p51 contains 440 amino acids and it is deliberated to stabilize the heterodimer but this unit also may take part in t-RNA primer binding ^{10, 11, 12}. The HIV-1RT catalyses replication of viral genome (mRNA) converting it into proviral DNA (cDNA) which gets integrated into the human genome present into the nucleus of an infected cell. The integration is catalysed by HIV-1 integrase. The ribonuclease H-domain of the larger subunit (p66) of HIV-1 RT degrades retroviral RNA while synthesising c DNA ^{10, 12}. Most of the anti-HIV-1 drugs have targeted the RT so as to block cDNA synthesis and hence further sequence of reactions concerning retroviral replication.

HIV-1 protease is another key enzyme which is essential for the HIV life-cycle ¹³. The protease cleaves the newly translated chain and generates required protein components to assemble the infectious HIV virions ^{13, 14}. HIV virions become uninfectious without operative HIV protease ^{15, 16}. Thus, the inhibition of the activity of HIV-1 or the mutation of the active site residues of HIV protease may disrupt the packaging and maturation of the viruses ¹⁷. Therefore, HIV protease becomes one of the main targets towards design and development of many new HIV-1 drugs in addition to the reverse transcriptase and integrase enzymes ¹⁸.

Various synthetic drugs are in practice against reverse transcriptase such as nucleoside / nucleotide reverse transcriptase inhibitors (Abacavir, Didanosine, Emtricitabine, Lamivudine, Stavudine, Tenofovir, Zidovudine) and non-nucleoside reverse transcriptase inhibitors (NNRTI) (efavirenze, nevirapine, delavirdine and etravirdine). The drugs against HIV-1 protease include saquinavir, ritonavir, indinavir, and nelfinavir. The applications of these synthetic drugs are reported to develop drug resistance in HIV and also the emergence of the new species of the virus ^{19, 20}. The approved anti HIV synthetic drugs are effective in the early phase but during the course of time the efficacy starts decreasing. Therefore, it is a necessity to develop a cost-effective, potential anti-HIV drug with easy availability from the other sources rather than the synthetic source. The natural compounds may prove as the promising alternative options to develop a new anti-HIV drug with negligible side effects and higher efficacy. Various phytochemicals such as curcumin, geranin, gallotannin, tiliroside, kaempferol-3-o-glucoside and trachelogenin etc. have been evaluated for the in-silico analysis against HIV-1 ²¹. The aim of molecular docking is to estimate the realistic binding geometries of a proposed ligand with a target with known target site. Characterization of the binding site, appropriate orientation of the ligand into the binding site and estimation of the strength of interaction of ligand-receptor complex is the main task of the molecular docking. Recently most of the drugs in the market are either derived from the natural sources or semi-synthetic in nature ²¹. Some analogues of the natural compounds for some new targets in HIV-1 may be developed as the new anti HIV drugs. Since metals and metal-complexes have been used to cure the several critical diseases, therefore, metal-based therapy may be the next step to treat the HIV/AIDS ²². The use of phytochemicals to be explored as anti-HIV agents could be another viable option.

Carissa carandas Linn. (family; Apocynaceae) is commonly known as Karonda. C. carandas, commonly present in India and other Asian countries ²³. Fruits and leaves are known for presence of various pharmacologically important phytochemicals ²⁴. The extract of different parts of this plant is used for the cure of various ailments. From the extracts of different parts of C. carandas few potential phytocompounds named as carandinol, carrinsone, carindone, lupeol etc. were identified and isolated ^{25, 26}. In the present paper, we have presented the qualitative characterization of different extracts of leaves and fruits of C. carandas using solvents of varying polarities such as hexane, ethanolic, methanolic, and aqueous. Using some known molecules from this plant as ligands and HIV-1 RT and HIV-1 protease as targets, the in-silico analysis has been carried out in order to assess their prospective applications as effective anti-HIV-1 regimen in future.

The plant extracts of C. carandas showed the presence of many phytochemicals. Phytochemical screening of the leaves and root extracts of this plant has been reported by Sawant and Godghate ¹⁹. Qualitative characterization has also been reported in other plants and presence of phytochemicals has been also reported in other plants ^{29, 33}.

Carandinol showed the highest inhibition activity and rutin the least inhibition activity against both 1REV and 1 EBY. The inhibition potential of ligand depends upon the active sites of molecules and structure of ligands. Molecular docking was also performed by other worker against HIV-1 RT ²¹ and HIV-1 integrase ³⁴ and reported the significant anti-HIV activity of phytochemicals. In-silico analysis of Dolichin A and B against HIV-RT was also evaluated ³⁵.

From the present study several compounds were screened in the leaf and fruit extracts. In this work, molecular docking was performed by phytocompounds with both HIV-1 reverse transcriptase and HIV-1 protease. Based on the 3D structure obtained from PDB, the molecular docking was used to produce the binding pose of best docked structure. Total nine compounds were used for molecular docking and among all the carandinol exhibited to be the most potential inhibitor against 1REV and 1EBY. Based on the molecular docking results, it was evident that carandinol possessed lowest binding energy of -10.11 kcal/mole with HIV-1 reverse transcriptase and -10.99 kcal/mole with HIV-1 protease. Inhibition of 1REV and 1EBY proved that the plant extract of C. carandas had the anti-HIV potential. Hence, it can be exploited to develop more effective and potential anti-HIV drugs.

RS and BS conceived the idea on subject of research mentioned in the manuscript. RS performed the phytochemical characterization. RS and AN performed the docking study. All the authors have contributed in preparation and editing of the manuscript.

RS is grateful to DST-New Delhi for financial support in the form of N-PDF (PDF/2016/000061). BS is grateful to UPCST-Lucknow for financial support in the form of a research grant.