Dendrimers are hyperbranched, monodispersed macromolecules with multivalent functional end groups. Dendrimers have been explored as carrier for many drugs like anticancer, antiviral, antimalarial, antiprotozoal, anti tubercular drugs. Although a number of different types of dendrimers containing different core molecules, branching monomers and surface functional groups have been designed till date for drug delivery applications, yet the poly(propyleneimine) (PPI) and poly(amidoamine) (PAMAM) dendrimers have been the most explored dendrimers in this regard. In this review, we have summarized a comparative data on PPI and PAMAM dendrimers particularly relevant to their properties, synthesis, toxicity, biomedical applications and drug delivery attributes.

The novel bis‐condensed heterocyclic systems with ring assemblies based on peripheral barbituric acid rings and central pyran, pyridine and thiine rings have been generated by the reaction of terephthalaldehyde and isophthalaldehyde with barbituric acid for comparison with the analogous systems generated with said dialdehydes and 1,3‐cyclohexanedione.

The novel bis-condensed heterocyclic systems with ring assemblies based on peripheral barbituric acid rings and central pyran, pyridine and thiine rings have been generated by the reaction of terephthalaldehyde and isophthalaldehyde with barbituric acid for comparison with the analogous systems generated with said dialdehydes and 1,3-cyclohexanedione. Carbonyl compounds especially the aldehydes and to large extent ketones also condense with cyclic reactive methylene compounds to produce olefins [1][2]. This is an excellent method for generation of carbon-carbon double bonds. These reactions are generally base or acid catalysed. Literature search reveals that a fair amount of work has been published on the reaction of aromatic monoaldehyde with active methylene compounds [3][4][5][6][7][8][9]. In the present article, we are reporting and highlighting the reaction of barbituric acid as an active methylene pyrimidine derivative with terephthalaldehyde and isophthalaldehyde in N,N-dimethyl formamide (DMF). When terephthalaldehyde and isophthalaldehyde were treated with barbituric acid under different conditions novel pyran, pyridine and thiine based heterocyclic ring assemblies were generated probably via the intermediacy of normal Knoevenagel reaction, Michael addition and cyclodehydratioon. With phthalaldehyde, a mixture of products was obtained and due to poor yield because of over crowding, the products could not be separated.When the two aromatic dialdehydes were treated with 1,3-cyclohexanedione under different conditions in ethylene glycol as reported [10] with dimedone and [11] for the synthesis of bifunctional pyridine and quinoline derivatives under similar conditions; bis-xanthene, bisacridine and bis-thioxanthene ring assemblies were generated as expected. Comparative yields in two different solvent systems for two sets of reactions have been recorded in Table 1. The reactions are shown in Scheme 1. All the compounds obtained gave analysis for C, H, N and S in good agreement with calculated values, and the structures were established on the basis of spectroscopic data.Results and Discussion.Using only terephthalaldehyde and barbituric acid in DMF as such; in presence of NH 4 OAc, NH 2 OH.HCl, and NaOAc and P 2 S 5 , the condensed ring assembly compounds 2a, 3a, 4a and 5a respectively were obtained in good yield under thermal conditions. Using isophthalaldehyde and barbituric acid under exactly similar conditions the novel compounds 2b, 3b, 4b and 5b were obtained. With 1,3-cyclohexanedione and terephthalaldehyde under analogues conditions using ethylene glycol solvent, the ring assembly compounds 6a,7a, 8a and 9a were obtained. 1,3-Cyclohexanedione and isophthalaldehyde under different conditions in the ethylene glycol furnished the compounds 6b, 7b ,8b and 9b.It has been summarised under the present exposition that DMF is suitable solvent for barbituric acid as a synthon and ethylene glycol is the most suitable solvent for cyclohexanedione as the synthon. P 2 S 5 in the synthesis of thio compunds 5a, 5b,...