We previously reported a milestone in the optimization of NBD-11021, an HIV-1 gp120 antagonist, by developing a new and novel analogue, NBD-14189 (Ref1), which showed antiviral activity against HIV-1 HXB2 , with a half maximal inhibitory concentration of 89 nM. However, cytotoxicity remained high, and the absorption, distribution, metabolism, and excretion (ADME) data showed relatively poor aqueous solubility. To optimize these properties, we replaced the phenyl ring in the compound with a pyridine ring and synthesized a set of 48 novel compounds. One of the new analogues, NBD-14270 (8), showed a marked improvement in cytotoxicity, with 3-fold and 58-fold improvements in selectivity index value compared with that of Ref1 and NBD-11021, respectively. Furthermore, the in vitro ADME data clearly showed improvements in aqueous solubility and other properties compared with those for Ref1. The data for 8 indicated that the pyridine scaffold is a good bioisostere for phenyl, allowing the further optimization of this molecule.

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The envelope glycoprotein gp120 of human immunodeficiency virus type 1 (HIV‐1) plays a critical role in virus entry to the cells by binding to the host cellular protein CD4. Earlier, we reported the design and discovery of a series of highly potent small‐molecule entry antagonists containing a thiazole ring (Scaffold A). Since this thiazole ring connected with an ethyl amide linkage represents the molecule‘s flexible part, we decided to explore substituting Scaffold A with two other positional isomers of the thiazole ring (Scaffold B and C) to evaluate their effect on the antiviral potency and cellular toxicity. Here we report the novel synthesis of two sets of positional thiazole isomers of the NBD‐14270 by retrosynthetic analysis approach, their anti‐HIV‐1 activity, cellular toxicity, and structure‐activity relationships. The study revealed that Scaffold A provided the best HIV‐1 inhibitors with higher potency and better selectivity index (SI).

Medicinal chemists are keen to explore tridimensional compounds, especially when it comes to small molecules. It has already been stressed that the majority of known drugs tend to be flat, whereas natural products tend to be more tridimensional and represent a good source of active compounds. 3D metrics have been implemented and computational descriptors are available to evaluate and prioritize compounds based on their 3D geometry. This is usually done by comparing the saturated carbon atoms in a molecule with the total number of its non‐hydrogen atoms (the Fsp3 value). While this aspect is clear, still there are not enough synthetic tools that support the realization of novel chemotypes that conform to these criteria. Herein we describe a diversity oriented synthesis (DOS) synthetic cascade technology that starts from two simple reagents, and generates highly enriched Fsp3 novel and diverse spiro‐scaffolds with pragmatic synthetic handles (points of diversity). The spiro nature of these scaffolds not only ensures high Fsp3 values but renders the compounds more rigid and therefore more effective in forming precise stereo‐interactions with their potential biological targets. These compounds were also profiled for their drug‐like properties and as potential modulators of the NNMT enzyme.

The title compound (1RS,2RS,6RS)-2-(6-Amino-9H-purin-9-yl)-8-azaspiro[5.6]dodec-10-en-1-ol dihydrochloride was synthesized for the first time in two steps, the first of which was a regioselectivity of epoxide ring-opening reaction under the action of adenine, yielding N-tert-butoxycarbonyl-((1RS,2RS,6RS)-2-(6-amino-9H-purin-9-yl)-8-azaspiro[5.6]dodec-10-en-1-ol. By treating the latter with a saturated methanolic solution of hydrogen chloride, it was possible to obtain ((1RS,2RS,6RS)-2-(6-Amino-9H-purin-9-yl)-8-azaspiro[5.6]dodec-10-en-1-ol dihydrochloride. The features of the molecular and crystal structure of ((1RS,2RS,6RS)-2-(6-Amino-9H-purin-9-yl)-8-azaspiro[5.6]dodec-10-en-1-ol dihydrochloride are discussed based on X-ray diffraction studies. The product overall yield was 40% out of two steps and after purification by column chromatography and recrystallization. The product was characterized by 1H-NMR, 13C-NMR, IR spectroscopy, HRMS and X-ray.

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The Front Cover shows the interactions of the HIV‐1 envelope glycoprotein gp120 with two sets of NBD compounds (HIV‐1 entry inhibitors) representing three positional isomers. The primary goals of this work were to determine whether positional isomers of the thiazole ring in one of the lead inhibitors, NBD‐14270, may lead to an improvement in antiviral potency and cytotoxicity, and to derive SAR information. More information can be found in the Research Article by Alexander V. Kurkin, Andrea Altieri, Asim K. Debnath et al.