There is no truth in __________ claims even though they have been cleverly stated.

The blank requires a determiner that points to specific claims being discussed. 'These' is a demonstrative determiner referring to claims already mentioned or implied in context, which fits naturally. 'Thus' is an adverb meaning 'in this way', not a determiner. 'There' is an adverb of place, not a determiner. 'Supposed' is an adjective but does not idiomatically combine with 'no truth in supposed claims' in the way the sentence requires. Hence, 'these' is the most appropriate choice.